"Platform" by "Brian Crawford" on Flickr

Cross Platform Decision Records/Architectural Decision Records – a HowTo Guide

Several months ago, I wrote a post talking about Architectural Decision Records with adr-tools, but since then I’ve moved on a bit with things, so I wanted to write about alternatives.

I also wanted to comment a bit on why I use the term “Decision Records” (always “decision record”, never “DR” due to the overloading of that particular abbreviation) rather than “Architectural Decision Records” (ADR), but I’ll get to that towards the end of the post 😊

Using Decision Records the Manual Way

A decision record is usually basically a text file, using the “Markdown” format, which has several “standard” blocks of text in it. The “npryce” version, which most people use, has the following sections in it:

  1. Title (as a “level 1” heading) which also holds the date of the record.
  2. A (level 2 heading) status section, holding the status of this decision (and any links to documents which supersede or relate to this decision).
  3. The context of the decision.
  4. The decision.
  5. The consequences of that decision.

So, somewhat understandably, your organisational tooling should support you making your own documents, without using those tools.

There are conventions about how the index-critical details will be stored:

  1. Your title block should follow the format # 1. Decision Title. The # symbol means it is the primary heading for the document, then the number, which should probably be lower than 9999, is used as an index for linking to other records and then the text of the title should also be the name of the file you’ve created. In this case, it will likely be 0001-decision-title.md.
  2. The status will usually be one of: Approved or Proposed. If a document is superseded, it should remove this status. Any other link type will live under the line showing the current status.

So, there’s no reason why you couldn’t just use this template for any files you create:

# NUMBER. TITLE

Date: yyyy-mm-dd

## Status

Accepted
Superseded by [2. Another Decision](0002-another-decision.md)

## Context

The context of the decision.

## Decision

The decision.

## Consequences

The consequences of that decision.

BUT, that’s not very automated, is it?

ADRs using Bash

Of course, most people making decision records use the Bash command line….. right? Oh, perhaps not. I’ll get back to you in a tic. If you’re using Bash, the “npryce” tooling I mentioned above is the same one I wrote about those months ago. So, read that, and then crack on with your ADRs.

ADRs using Powershell

So, if you’re using Windows, you might be tempted to find a decision record tool for Powershell. If so, I found “ajoberstar” on Github had produced just such a thing, and you “just”, as an administrator, run:

Install-Module -Name ArchitectureDecisionRecords
Set-ExecutionPolicy -ExecutionPolicy RemoteSigned

Then edit the script you installed (in C:\Program Files\WindowsPowerShell\Modules\ArchitectureDecisionRecords\0.1.1\ArchitectureDecisionRecords.psm1) and search-and-replace UTF8NoBOM for UTF8 and then save it…

And then you can run commands like Initialize-Adr or New-Adr -Title 'Use a database'. However, this script was last touched on 2nd July 2018, and although I’ve raised a few issues, they don’t seem to have been resolved (see also replacing UTF8NoBOM above).

ADRs using VSCode

By far, so far, the best tooling I’ve seen in this space is the adr-tools extension for VSCode. It too, however, has it’s own caveats, but these are not disastrous. Essentially, you need to create a path in which you store the template to use. You can get this from his own repo, here: https://github.com/vincent-ledu/adr-template.git and put it in .adr-templates in the root directory of your project. This, however, is customizable, by going to the settings for your user or workspace, searching for ADR and adjusting the paths accordingly.

A settings pane showing the Adr paths in your project’s tree

To add a new decision record, press Ctrl+Shift+P or click the cog icon in the sidebar, and select “Command Palette…”

Opening the Command Palette in VS Code

Then start typing “adr” to select from “ADR New”, “ADR Init”, “ADR Change Status” or “ADR Link”.

The Command Palette showing your options for commands to run

All of these will walk you through some options at the top of the screen, either asking for some text input, or asking you to select between options.

You may be tempted to just run this up now, and select “ADR New”, and it’ll look like it’s working, but, you first need to have obtained the template and create the directory structure. Selecting “ADR Init” will create the directory structure for your project and will try to perform a git clone of the repo mentioned above, but if you are already in a git repository, or you have some form of MITM proxy in the way, this will also break silently. The easiest thing to do is to either manually create the paths in your tree, according to what you have set or selected, or just run the ADR init, and then obtain the template from the git repo.

Talking of templates, in the previous scripts, the script would come with a template file built-in, and it would do a simple string replacement of the values “NUMBER”, “TITLE” and “STATUS”. With this script it instead uses it’s own template, which is stored in your project’s file tree, and uses parameter substitution, finding strings wrapped in pairs of curled braces (like {{ this }}). The downside to this is that you can’t just reuse the template I listed above… but no worries, get the file from the repo and stick it in your tree where it’s expecting it, or let the adr init function clone the template into your path – job done.

What other options are there?

Well, actually, this comes down to why I’m using the term “decision records” rather than “architectural decision record”, because I’m writing my own tool, and all the “adr” namespaces on Github were taken, and I’d seen a fair amount of posts suggesting that the “A” in “ADR” should stand for “Any”.. and I figured why should it exist at all?

The tool I’ve written so far is written in Javascript, and is starting from a (somewhat loose) TDD development process. It’s here: https://github.com/DecisionRecords/javascript-decision-records

Why Javascript? Frankly, I needed to learn a modern programming language, and wanted to apply it to a domain I was interested in. It’s currently not complete, it creates the record path and a configuration file, and I’m currently writing the functions to create new records. Also, because it’s Javascript, in theory I can also use the internals to create a VSCode extension with this later… MUCH later!

Why re-implement this at all? Firstly, it looks like most of the development work on those projects halted around 3-4 years ago, with no further interest in updating them to resolve bugs and issues. I didn’t want to fork the projects as-is, as I think they were largely written to scratch a particular itch (which is fine!) but they all miss key things I want to provide, like proper unit testing (only the npryce project comes close to this), internationalisation (none of them have this) and the ability to use a company- or project-wide template (only the VSCode extension does this). I also saw requests to support alternative file formats (like Restructured Text, which was completely rejected) and realised that if you built the script in such a way that these alternate formats could be used, then there was no reason not to support that.

In summary

There are tools you can use, whatever platform you’re using. My preference is the VSCode extension, and eventually will (hopefully!!) be the script I’m writing… but it’s not ready, yet.

Featured image is β€œPlatform” by β€œBrian Crawford” on Flickr and is released under a CC-BY license.

"Bat Keychain" by "Nishant Khurana" on Flickr

Unit Testing Bash scripts with BATS-Core

I’m taking a renewed look into Unit Testing the scripts I’m writing, because (amongst other reasons) it’s important to know what expected behaviours you break when you make a change to a script!

A quick detour – what is Unit Testing?

A unit test is where you take one component of your script, and prove that, given specific valid or invalid tests, it works in an expected way.

For example, if you normally run sum_two_digits 1 1 and expect to see 2 as the result, with a unit test, you might write the following tests:

  • sum_two_digits should fail (no arguments)
  • sum_two_digits 1 should fail (no arguments)
  • sum_two_digits 1 1 should pass!
  • sum_two_digits 1 1 1 may fail (too many arguments), may pass (only sum the first two digits)
  • sum_two_digits a b should fail (not numbers)

and so on… you might have seen this tweet, for example

Things you might unit test in a bar.

Preparing your environment

Everyone’s development methodology differs slightly, but I create my scripts in a git repository.

I start from a new repo, like this:

mkdir my_script
cd my_script
git init

echo '# `my_script`' > README.md
echo "" >> README.md
echo "This script does awesome things for awesome people. CC-0 licensed." >> README.md
git add README.md
git commit -m 'Added README'

echo '#!/bin/bash' > my_script.sh
chmod +x my_script.sh
git add my_script.sh
git commit -m 'Added initial commit of "my_script.sh"'

OK, so far, so awesome. Now let’s start adding BATS. (Yes, this is not necessarily the “best” way to create your “test_all.sh” script, but it works for my case!)

git submodule add https://github.com/bats-core/bats-core.git test/libs/bats
git commit -m 'Added BATS library'
echo '#!/bin/bash' > test/test_all.sh
echo 'cd "$(dirname "$0")" || true' >> test/test_all.sh
echo 'libs/bats/bin/bats $(find *.bats -maxdepth 0 | sort)' >> test/test_all.sh
chmod +x test/test_all.sh
git add test/test_all.sh
git commit -m 'Added test runner'

Now, let’s write two simple tests, one which fails and one which passes, so I can show you what this looks like. Create a file called test/prove_bats.bats

#!/usr/bin/env ./libs/bats/bin/bats

@test "This will fail" {
  run false
  [ "$status" -eq 0 ]
}

@test "This will pass" {
  run true
  [ "$status" -eq 0 ]
}

And now, when we run this with test/test_all.sh we get the following:

 βœ— This will fail
   (in test file prove_bats.bats, line 5)
     `[ "$status" -eq 0 ]' failed
 βœ“ This will pass

2 tests, 1 failure

Excellent, now we know that our test library works, and we have a rough idea of what a test looks like. Let’s build something a bit more awesome. But first, let’s remove prove_bats.bats file, with rm test/prove_bats.bats.

Starting to develop “real” tests

Let’s create a new file, test/path_checking.bats. Our amazing script needs to have a configuration file, but we’re not really sure where in the path it is! Let’s get building!

#!/usr/bin/env ./libs/bats/bin/bats

# This runs before each of the following tests are executed.
setup() {
  source "../my_script.sh"
  cd "$BATS_TEST_TMPDIR"
}

@test "No configuration file is found" {
  run find_config_file
  echo "Status received: $status"
  echo "Actual output:"
  echo "$output"
  [ "$output" == "No configuration file found." ]
  [ "$status" -eq 1 ]
}

When we run this test (using test/test_all.sh), we get this response:

 βœ— No configuration file is found
   (in test file path_checking.bats, line 14)
     `[ "$output" == "No configuration file found." ]' failed with status 127
   Status received: 127
   Actual output:
   /tmp/my_script/test/libs/bats/lib/bats-core/test_functions.bash: line 39: find_config_file: command not found

1 test, 1 failure

Uh oh! Well, I guess that’s because we don’t have a function called find_config_file yet in that script. Ah, yes, let’s quickly divert into making your script more testable, by making use of functions!

Bash script testing with functions

When many people write a bash script, you’ll see something like this:

#!/bin/bash
echo "Validate 'uname -a' returns a string: "
read_some_value="$(uname -a)"
if [ -n "$read_some_value" ]
then
  echo "Yep"
fi

While this works, what it’s not good for is testing each of those bits (and also, as a sideline, if your script is edited while you’re running it, it’ll break, because Bash parses each line as it gets to it!)

A good way of making this “better” is to break this down into functions. At the very least, create a “main” function, and put everything into there, like this:

#!/bin/bash
function main() {
  echo "Validate 'uname -a' returns a string: "
  read_some_value="$(uname -a)"
  if [ -n "$read_some_value" ]
  then
    echo "Yep"
  fi
}

main

By splitting this into a “main” function, which is called when it runs, at the very least, a change to the script during operation won’t break it… but it’s still not very testable. Let’s break down some more of this functionality.

#!/bin/bash
function read_uname() {
  echo "$(uname -a)"
}
function test_response() {
  if [ -n "$1" ]
  then
    echo "Yep"
  fi
}
function main() {
  echo "Validate 'uname -a' returns a string: "
  read_some_value="$(read_uname)"
  test_response "$read_some_value"
}

main

So, what does this give us? Well, in theory we can test each part of this in isolation, but at the moment, bash will execute all those functions straight away, because they’re being called under “main”… so we need to abstract main out a bit further. Let’s replace that last line, main into a quick check.

if [[ "${BASH_SOURCE[0]}" == "${0}" ]]
then
  main
fi

Stopping your code from running by default with some helper variables

The special value $BASH_SOURCE[0] will return the name of the file that’s being read at this point, while $0 is the name of the script that was executed. As a little example, I’ve created two files, source_file.sh and test_sourcing.sh. Here’s source_file.sh:

#!/bin/bash

echo "Source: ${BASH_SOURCE[0]}"
echo "File: ${0}"

And here’s test_sourcing.sh:

#!/bin/bash
source ./source_file.sh

What happens when we run the two of them?

user@host:/tmp/my_script$ ./source_file.sh
Source: ./source_file.sh
File: ./source_file.sh
user@host:/tmp/my_script$ ./test_sourcing.sh
Source: ./source_file.sh
File: ./test_sourcing.sh

So, this means if we source our script (which we’ll do with our testing framework), $BASH_SOURCE[0] will return a different value from $0, so it knows not to invoke the “main” function, and we can abstract that all into more test code.

Now we’ve addressed all that lot, we need to start writing code… where did we get to? Oh yes, find_config_file: command not found

Walking up a filesystem tree

The function we want needs to look in this path, and all the parent paths for a file called “.myscript-config“. To do this, we need two functions – one to get the directory name of the “real” directory, and the other to do the walking up the path.

function _absolute_directory() {
  # Change to the directory provided, or if we can't, return with error 1
  cd "$1" || return 1
  # Return the full pathname, resolving symbolic links to "real" paths
  pwd -P
}

function find_config_file() {
  # Get the "real" directory name for this path
  absolute_directory="$(_absolute_directory ".")"
  # As long as the directory name isn't "/" (the root directory), and the
  #  return value (config_path) isn't empty, check for the config file.
  while [ "$absolute_directory" != "/" ] && 
        [ -n "$absolute_directory" ] && 
        [ -z "$config_path" ]
  do
    # Is the file we're looking for here?
    if [ -f "$absolute_directory/.myscript-config" ]
    then
      # Store the value
      config_path="$absolute_directory/.myscript-config"
    else
      # Get the directory name for the parent directory, ready to loop.
      absolute_directory="$(_absolute_directory "$absolute_directory/..")"
    fi
  done
  # If we've exited the loop, but have no return value, exit with an error
  if [ -z "$config_path" ]
  then
    echo "No config found. Please create .myscript-config in your project's root directory."
    # Failure states return an exit code of anything greater than 0. Success is 0.
    exit 1
  else
    # Output the result
    echo "$config_path"
  fi
}

Let’s re-run our test!

 βœ— No configuration file is found
   (in test file path_checking.bats, line 14)
     `[ "$output" == "No configuration file found." ]' failed
   Status received: 1
   Actual output:
   No config found. Please create .myscript-config in your project's root directory.

1 test, 1 failure

Uh oh! Our output isn’t what we told it to use. Fortunately, we’ve recorded the output it sent (“No config found. Please...“) so we can fix our test (or, find that output line and fix that).

Let’s fix the test! (The BATS test file just shows the test we’re amending)

@test "No configuration file is found" {
  run find_config_file
  echo "Status received: $status"
  echo "Actual output:"
  echo "$output"
  [ "$output" == "No config found. Please create .myscript-config in your project's root directory." ]
  [ "$status" -eq 1 ]
}

Fab, and now when we run it, it’s all good!

user@host:/tmp/my_script$ test/test_all.sh
 βœ“ No configuration file is found

1 test, 0 failures

So, how do we test what happens when the file is there? We make a new test! Add this to your test file, or create a new one, ending .bats in the test directory.

@test "Configuration file is found and is OK" {
  touch .myscript-config
  run find_config_file
  echo "Status received: $status"
  echo "Actual output:"
  echo "$output"
  [ "$output" == "$BATS_TEST_TMPDIR/.myscript-config" ]
  [ "$status" -eq 0 ]
}

And now, when you run your test, you’ll see this:

user@host:/tmp/my_script$ test/test_all.sh
 βœ“ No configuration file is found
 βœ“ Configuration file is found and is OK

2 tests, 0 failures

Extending BATS

There are some extra BATS tests you can run – at the moment you’re doing manual checks of output and success or failure checks which aren’t very pretty. Let’s include the “assert” library for BATS.

Firstly, we need this library added as a submodule again.

# This module provides the formatting for the other non-core libraries
git submodule add https://github.com/bats-core/bats-support.git test/libs/bats-support
# This is the actual assertion tests library
git submodule add https://github.com/bats-core/bats-assert.git test/libs/bats-assert

And now we need to update our test. At the top of the file, under the #!/usr/bin/env line, add these:

load "libs/bats-support/load"
load "libs/bats-assert/load"

And then update your tests:

@test "No configuration file is found" {
  run find_config_file
  assert_output "No config found. Please create .myscript-config in your project's root directory."
  assert_failure
}

@test "Configuration file is found and is OK" {
  touch .myscript-config
  run find_config_file
  assert_output "$BATS_TEST_TMPDIR/.myscript-config"
  assert_success
}

Note that we removed the “echo” statements in this file. I’ve purposefully broken both types of tests (exit 1 became exit 0 and the file I’m looking for is $absolute_directory/.config instead of $absolute_directory/.myscript-config) in the source file, and now you can see what this looks like:

 βœ— No configuration file is found
   (from function `assert_failure' in file libs/bats-assert/src/assert_failure.bash, line 66,
    in test file path_checking.bats, line 15)
     `assert_failure' failed

   -- command succeeded, but it was expected to fail --
   output : No config found. Please create .myscript-config in your project's root directory.
   --

 βœ— Configuration file is found and is OK
   (from function `assert_output' in file libs/bats-assert/src/assert_output.bash, line 194,
    in test file path_checking.bats, line 21)
     `assert_output "$BATS_TEST_TMPDIR/.myscript-config"' failed

   -- output differs --
   expected : /tmp/bats-run-21332-1130Ph/suite-tmpdir-QMDmz6/file-tmpdir-path_checking.bats-nQf7jh/test-tmpdir--I3pJYk/.myscript-config
   actual   : No config found. Please create .myscript-config in your project's root directory.
   --

And so now you can see some of how to do unit testing with Bash and BATS. BATS also says you can unit test any command that can be run in a Bash environment, so have fun!

Featured image is “Bat Keychain” by “Nishant Khurana” on Flickr and is released under a CC-BY license.

"Picture in Picture" by "Mats" on Flickr

Hints and Tips when using Vagrant on Windows

I’ve been using HashiCorp’s Vagrant with Oracle’s VirtualBox for several years (probably since 2013, if my blog posts are anything to go by), and I’ve always been pretty comfortable with how it works.

This said, when using a Windows machine running Microsoft’s Hyper-V (built into Windows since Windows 7/2018) VirtualBox is unable (by default) to run 64 bit virtual machines (thanks to Hyper-V “stealing” the VT-x/AMD-V bit from the BIOS/EFI).

Around last year or maybe even the year before, Microsoft introduced a “Hypervisior Platform” add-on, which lets VirtualBox run 64 bit machines on a Hyper-V host (more on this later). HOWEVER, it is much slower than in native mode, and can often freeze on booting…

Meanwhile, Vagrant, (a configuration file that acts as a wrapper around various hypervisors, using VirtualBox by default) boots machines in a “headless” mode by default, so you can’t see the freezing.

I’m trying to use an Ubuntu 18.04 virtual machine for various builds I’m creating, and found that I’d get a few issues on boot, so let’s get these sorted out.

VirtualBox can’t start 64bit virtual machines when Hyper-V is installed.

You need to confirm that certain Windows features are enabled, including “Hyper-V” and “Windows Hypervisor Platform”. Confirm you’re running at least Windows 10 version 1803 which is the first release with the “Windows Hypervisor Platform”.

GUI mode

Run winver to bring up this box. Confirm the version number is greater than 1803. Mine is 1909.

A screenshot of the “winver” command, highlighting the version number, which in this case shows 1909, but needs to show at least 1803.

Right click on the start menu, and select “Apps and Features”. Click on “Programs and Features”.

The settings panel found by right clicking the “Start Menu” and selecting “Apps and Features”. Note the desired next step – “Programs and Features” is highlighted.

In the “Programs and Features” window, click on “Turn Windows Features on or off”. Note the shield icon here indicates that administrative access is required, and you may be required to authenticate to the machine to progress past this stage.

A fragment of the “Programs and Features” window, with the “Turn Windows features on or off” link highlighted.

Next, ensure that the following “Windows Features” are enabled; “Hyper-V”, “Virtual Machine Platform” and “Windows Hypervisor Platform”. Click on “OK” to install these features, if they’re not already installed.

A screen capture of the “Turn Windows features on or off” dialogue box, with certain features obscured and others highlighted.

Note that once you’ve pressed “OK”, you’ll likely need to reboot your machine, if any of these features were not already installed.

CLI mode

Right click on the start menu, and start an Administrative Powershell session.

Run the command Get-ComputerInfo | select WindowsVersion. You should get a response which looks like this:

WindowsVersion
--------------
1909

Note that the version number needs to be greater than 1803.

Next, find the names of the features you need to install. These features have region specific names, so outside EN-GB, these names may not match your requirements!

Run the command Get-WindowsOptionalFeature -online | select FeatureName,State and you’re looking for the following lines (this has been cropped to just what you need):

FeatureName                                     State
-----------                                     -----
HypervisorPlatform                            Enabled
VirtualMachinePlatform                        Enabled
Microsoft-Hyper-V-All                         Enabled

If any of these three features are not enabled, run Enable-WindowsOptionalFeature -online -FeatureName x where “x” is the name of the feature, listed in the above text block, you want to install. For example: Enable-WindowsOptionalFeature -online -FeatureName HypervisorPlatform,VirtualMachinePlatform,Microsoft-Hyper-V-All. If you run this when they’re already enabled, it should return RestartNeeded : False, but otherwise you’re likely to need to reboot.

After the reboot

After you’ve rebooted, and you start a 64 bit virtual machine in VirtualBox, you’ll see this icon in the bottom corner.

A screen grab of the VirtualBox Status Bar, highlighting the “Slow Mode” icon representing the CPU

Booting the Virtual Machine with Vagrant fails because it takes too long to boot

This was historically a big issue with Vagrant and VirtualBox, particularly with Windows Vagrant boxes, but prior to the Hyper-V/VirtualBox solution, it’d been largely fixed (or at least, I wasn’t seeing it!) There is a “standard” timeout for booting a Virtual Machine, I think at approximately 5 minutes, but I might be wrong. To make this “issue” stop occurring, add this config.vm.boot_timeout = 0 line to your Vagrantfile, like this:

Vagrant.configure("2") do |config|
  config.vm.boot_timeout = 0
end

This says to Vagrant, don’t worry how long it takes to boot, just keep waiting until it does. Yes, it will be slower, but it should get there in the end!

Booting the Virtual Maching with Vagrant does not fail, but it never authenticates with your Private Key.

Your VM may sit at this block for quite a while:

==> default: Waiting for machine to boot. This may take a few minutes...
    default: SSH address: 127.0.0.1:2222
    default: SSH username: vagrant
    default: SSH auth method: private key

If this occurs, you may find that your virtual machine has hung during the boot process… but weirdly, a simple work-around to this is to ensure that the VirtualBox GUI is open, and that you’ve got a block like this (config.vm.provider / vb.gui=true / end) in your Vagrantfile:

Vagrant.configure("2") do |config|
  config.vm.provider "virtualbox" do |vb|
    vb.gui = true
  end
end

This forces VirtualBox to open a window with your Virtual Machine’s console on it (much like having a monitor attached to real hardware). You don’t need to interact with it, but any random hangs or halts on your virtual machine may be solved just by bringing this window, or the VirtualBox Machines GUI, to the foreground.

Sometimes you may see, when this happens, a coredump or section of kernel debugging code on the console. Don’t worry about this!

Vagrant refuses to SSH to your virtual machine when using the vagrant ssh command.

Provisioning works like a treat, and you can SSH into the virtual machine from any other environment, but, when you run vagrant ssh, you get an error about keys not being permitted or usable. This is fixable by adding a single line, either to your system or user -wide environment variables, or by adding a line to your Vagrantfile.

The environment variable is VAGRANT_PREFER_SYSTEM_BIN, and by setting this to 0, it will use bundled versions of ssh or rsync instead of using any versions provided by Windows.

You can add a line like this ENV['VAGRANT_PREFER_SYSTEM_BIN']="0" to your Vagrantfile, outside of the block Vagrant.configureend, like this:

ENV['VAGRANT_PREFER_SYSTEM_BIN']="0"
Vagrant.configure("2") do |config|
end

Sources

Featured image is β€œPicture in Picture” by β€œMats” on Flickr and is released under a CC-BY-SA license.

"2015_12_06_VisΓ©_135942" by "Norbert Schnitzler" on Flickr

Idea for Reusable “Custom Data” templates across multiple modules with Terraform

A few posts ago I wrote about building Windows virtual machines with Terraform, and a couple of days ago, “YoureInHell” on Twitter reached out and asked what advice I’d give about having several different terraform modules use the same basic build of custom data.

They’re trying to avoid putting the same template file into several repos (I suspect so that one team can manage the “custom-data”, “user-data” or “cloud-init” files, and another can manage the deployment terraform files), and asked if I had any suggestions.

I had three ideas.

Using a New Module

This was my initial thought; create a new module called something like “Standard Build File”, and this build file contains just the following terraform file, and a template file called “build.tmpl”.

variable "someKey" {
  default = "someVar"
}

variable "hostName" {
  default = "hostName"
}

variable "unsetVar" {}

output "template" {
  value = templatefile("build.tmpl",
    {
      someKey  = var.someKey
      hostName = var.hostName
      unsetVar = var.unsetVar
    }
  )
}

Now, in your calling module, you can do:

module "buildTemplate" {
  source   = "git::https://git.example.net/buildTemplate.git?ref=latestLive"
  # See https://www.terraform.io/docs/language/modules/sources.html
  #   for more details on how to specify the source of this module
  unsetVar = "Set To This String"
}

output "RenderedTemplate" {
  value = module.buildTemplate.template
}

And that means that you can use the module.buildTemplate.template anywhere you’d normally specify your templateFile, and get a consistent, yet customizable template (and note, because I specified a particular tag, you can use that to move to the “current latest” or “the version we released into live on YYYY-MM-DD” by using a tag, or a commit ref.)

Now, the downside to this is that you’ve now got a whole separate module for creating your instances that needs to be maintained. What are our other options?

Git Submodules for your template

I use Git Submodules a LOT for my code. It’s a bit easy to get into a state with them, particularly if you’re not great at keeping on top of them, but… if you are OK with them, you’d create a repo, again, let’s use “https://git.example.net/buildTemplate.git” as our git repo, and put your template in there. In your terraform git repo, you’d run this command: git submodule add https://git.example.net/buildTemplate.git and this would add a directory to your repo called “buildTemplate” that you can use your templatefile function in Terraform against (like this: templatefile("buildTemplate/build.tmpl", {someVar="var"})).

Now, this means that you’ve effectively got two git repos in one tree, and if any changes occur in your submodule repo, you’d need to do git checkout main ; git pull to get the latest updates from your main branch, and when you check it out initially on another machine, you’ll need to do git clone https://git.example.net/terraform --recurse-submodules to get the submodules populated at the same time.

A benefit to this is that because it’s “inline” with the rest of your tree, if you need to make any changes to this template, it’s clearly where it’s supposed to be in your tree, you just need to remember about the submodule when it comes to making PRs and suchforth.

How about that third idea?

Keep it simple, stupid 😁

Why bother with submodules, or modules from a git repo? Terraform can be quite easy to over complicate… so why not create all your terraform files in something like this structure:

project\build.tmpl
project\web_servers\main.tf
project\logic_servers\main.tf
project\database_servers\main.tf

And then in each of your terraform files (web_servers, logic_servers and database_servers) just reference the file in your project root, like this: templatefile("../build.tmpl", {someVar="var"})

The downside to this is that you can’t as easily farm off the control of that build script to another team, and they’d be making (change|pull|merge) requests against the same repo as you… but then again, isn’t that the idea for functional teams? πŸ˜ƒ

Featured image is β€œ2015_12_06_VisΓ©_135942” by β€œNorbert Schnitzler” on Flickr and is released under a CC-BY-SA license.

"Router" by "Ryan Hodnett" on Flickr

Post-Config of a RaspberryPi Zero W as an OTG-USB Gadget that routes

In my last post in this series I mentioned that I’d got my Raspberry Pi Zero W to act as a USB Ethernet adaptor via libComposite, and that I was using DNSMasq to provide a DHCP service to the host computer (the one you plug the Pi into). In this part, I’m going to extend what local services I could provide on this device, and start to use this as a router.

Here’s what you missed last time… When you plug the RPi in (to receive power on the data line), it powers up the RPi Zero, and uses a kernel module called “libComposite” to turn the USB interface into an Ethernet adaptor. Because of how Windows and non-Windows devices handle network interfaces, we use two features of libComposite to create an ECM/CDC interface and a RNDIS interface, called usb0 and usb1, and whichever one of these two is natively supported in the OS, that’s which interface comes up. As a result, we can then use DNSMasq to “advertise” a DHCP address for each interface, and use that to advertise services on, like an SSH server.

By making this device into a router, we can use it to access the network, without using the in-built network adaptor (which might be useful if your in-built WiFi adaptors isn’t detected under Linux or Windows without a driver), or to protect your computer from malware (by adding a second firewall that doesn’t share the same network stack as it’s host), or perhaps to ensure that your traffic is sent over a VPN tunnel.

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"DeBugged!" by "Randy Heinitz" on Flickr

Debugging Bash Scripts

Yesterday I was struggling a bit with a bash script I was writing. I needed to stop it from running flat out through every loop, and I wanted to see what certain values were at key points in the script.

Yes, I know I could use “read” to pause the script and “echo” to print values, but that leaves a lot of mess that I need to clean up afterwards… so I went looking for something else I could try.

You can have extensive debug statements, which are enabled with a --debug flag or environment variable… but again, messy.

You can run bash -x ./myscript.sh – and, indeed, I do frequently do that… but that shows you the commands which were run at each point, not what the outcome is of each of those commands.

If my problem had been a syntax one, I could have installed shellcheck, which is basically a linter for Bash and other shell scripting languages, but no, I needed more detail about what was happening during the processing.

Instead, I wanted something like xdebug (from PHP)… and I found Bash Debug for VSCode. This doesn’t even need you to install any scripts or services on the target machine – it’s interactive, and has a “watch” section, where you either highlight and right-click a variable expression (like $somevar or ${somevar}) to see when it changes. You can see where in the “callstack” you are and see what values are registered by that script.

Shellcheck shows me problems in my code…
But Bash Debug helps me to find out what values are at specific points in the code.

All in all, a worthy addition to my toolbelt!

Featured image is β€œDeBugged!” by β€œRandy Heinitz” on Flickr and is released under a CC-BY license.

"Blueprints" by "Cameron Degelia" on Flickr

Using Architectural Decision Records (ADR) with adr-tools

Introducing Architectural Decision Records

Over the last week, I discovered a new tool for my arsenal called Architectural Decision Records (ADR). They were first written about in 2011, in a post called “Documenting Architecture Decisions“, where the author, Michael Nygard, advocates for short documents explaining each decision that influences the architecture of an environment.

I found this via a Github repository, created by the team at gov.uk, which includes their ADR library, and references the tool they use to manage these documents – adr-tools.

Late edit 2021-01-25: I also found a post which suggests that Spotify uses ADR.

Installing adr-tools on Linux

Currently adr-tools are easier to install under OSX rather than Linux or Windows Subsystem for Linux (WSL) (I’m working on this – bear with me! πŸ˜ƒ ).

The current installation notes suggest for Linux (which would also work on WSL) is to download the latest release tar.gz or zip file and unpack it into your path somewhere. This isn’t exactly the best way to deploy anything on Linux, but… I guess it works right now?

For me, I downloaded the file, and unpacked the whole tar.gz file (as root) into /usr/local/bin/, giving me a directory of /usr/local/bin/adr-tools-3.0.0/. There’s a subdirectory in here, called src which contains a large number of files – mostly starting _adr or adr- and two additional files, init.md and template.md.

Rather than putting all of these files into /usr/local/bin directly, instead I leave them in the adr-tools-3.0.0 directory, and create a symbolic link (symlink) to the /usr/local/bin directory with this command:

cd /usr/local/bin
ln -s adr-tools-3.0.0/src/* .

This gives me all those files in one place, so I can refer to them later.

An aside – why link everything in that src directory? (Feel free to skip this block!)

Now, why, you might ask, do all of these unrelated files need to be in the same place? Well…. the author of the script has put this in at the top of almost all the files:

#!/bin/bash
set -e
eval "$($(dirname $0)/adr-config)"

And then in that script, it says:

#!/bin/bash
basedir=$(cd -L $(dirname $0) > /dev/null 2>&1 && pwd -L)
echo "adr_bin_dir=$basedir"
echo "adr_template_dir=$basedir"

There are, technically, good reasons for this! This is designed to be run in, what in the Windows world, you might call as a “Portable Script”. So, you bung adr-tools into some directory somewhere, and then just call adr somecommand and it knows that all the files are where they need to be. The (somewhat) down side to this is that if you just want to call adr somecommand rather than path/to/my/adr somecommand then all those files need to be there

I’m currently looking to see if I can improve this somewhat, so that it’s not quite so complex to install, but for now, that’s what you need.

Anyway…

Using adr-tools to document your decisions

I’ll start documenting a fictional hosted web service project, and note down some of the decisions which have been made.

Initializing your ADR directory

Start by running adr init. You may want to specify a directory where you want to put these records, so instead use: adr init path/to/adr, like this:

Initializing the ADR in “documentation/architecture-decisions” with adr init documentation/architecture-decisions

You’ll notice that when I run this command, it creates a new entry, called 0001-record-architecture-decisions.md. Let’s open this up, and see what’s in here.

The VSCode record for the choice to use ADR. It is a markdown file, with the standard types of data recorded.

In here we have the record ID (1.), the title of the record Record architecture decisions, the date the choice was made Date: 2021-01-19, a status of Accepted, the context on why we made this choice, the decision, and the consequences of making this decision. Make changes, if needed, and save it. Let’s move on.

Creating our first own record

This all is quite straightforward thus far. Let’s create our next record.

Issuing the command adr new <sometitle> you create the next ADR record.

Let’s open up that record.

The template for the ADR record for “Use AWS”.

Like the first record, we have a title, a status, a context, decision and consequences. Let’s define these.

A “finished” brief ADR record.

This document shouldn’t be very long! It just describes why a choice was made and what that entails.

Changing decisions – completely replacing (superseding) a decision

Of course, over time, decisions will be replaced due to various decisions elsewhere.

You can ask adr to supersede a previous record, using the “-s” flag, and the record number.

Let’s look at how that works on the second ADR record.

After the command adr new -s 2 Use Azure, the ADR record number 2 has a new status, “Superceded by” and the superseded linked document. Yes, “Superceded” is a typo. There is an open PR for it

So, under the “Status”, where is previously said “Approved”, it now says “Superceded by [3. Use Azure](0003-use-azure.md)“. This is a markdown statement which indicates where the superseded document is located. As I mentioned in the comment below the above image, there is an open Pull Request to fix this on the adr-tools, so hopefully that typo won’t last long!

We’ve got our new ADR too – let’s take a look at that one?

Our new ADR shows that it “supercedes” the previous record. Which is good! Typo aside :)

Other references

Of course, you don’t always completely overrule a decision. Sometimes your decision is influenced by, or has a dependency on something else, like this one.

We know which provider we’re using at long last, now let’s pick a region. Use the -l flag to “link” between the referenced and new ADR. The context for the -l flag is “<number>:<text for link to number>:<text for link in targetted document>”.

The command here is:

adr new -l '3:Dependency:Influences' Use Region UK South and UK West

I’m just going to crop from the “Status” block on both the referenced ADR (3) and the ADR which references it (4):

Status block in ADR 0003 which is referenced by ADR 0004
Status block in the new ADR 0004 which references ADR 0003

And of course, you can also use the same switch to mark documents as partially obsoleted, like this:

adr new -l '4:Partially obsoletes:Partially obsoleted by' Use West Europe region instead of UK West region
Status block in ADR 0004 indicating it’s partially obsoleted. Probably worth updating the status properly to show it’s not just “Accepted”.

If you forget to add the referencing in, you can also use the adr link command, like this:

adr link 3 Influences 5 Dependency

To be clear, that command adds a (complete) line to ADR 0003 saying “Influences [5. ADR Title](link)” and a separate (complete) line to ADR 0005 saying “Dependency [3. ADR Title](link)“.

What else can we do?

There are four other “things” that it’s worth doing at this point.

  1. Note that you can change the template per-ADR directory.

Create a directory called “templates” in the ADR directory, and put a file in there called “template.md“. Tweak this as you need. Ensure you have AT LEAST the line ## Status and # NUMBER. TITLE as these are required by the script.

A much abbreviated template file, containing just “Number”, “Title”, “Date”, “Status”, and a new dummy heading called “Stuff”.
And the result of running adr new Some Text once you’ve created that template.

As you can see, it’s possible to add all sorts of content in this template as a result. Bear in mind, before your template turns into something like this, that it’s supposed to be a short document explaining why each decision was made, not a funding proposal, or a complex epic of your user stories!

Be careful not to let your template run away with you!
  1. Note that you can automatically open an editor, by setting the EDITOR (where the process is expected to finish before returning control, like using nano, emacs or vim, for example) or VISUAL (where the process is expected to “fork”, like for example, gedit or vscode) environment variable, and then running adr new A Title, like this:
  1. We can create “Table of Contents” files, using the adr generate toc command, like this:
Generating the table of contents, for injecting into other files.

This can be included into your various other markdown files. There are switches, so you can set the link path, but your best bet is to find that using adr help generate toc.

  1. We can also generate graphviz files of the link maps between elements of the various ADRs, like this: adr generate graph | dot -Tjpg > graph.jpg

If you omit the “| dot -Tjpg > graph.jpg” part, then you’ll see the graphviz output, which looks like this: (I’ve removed the documents 6 and 7).

digraph {
  node [shape=plaintext];
  subgraph {
    _1 [label="1. Record architecture decisions"; URL="0001-record-architecture-decisions.html"];
    _2 [label="2. Use AWS"; URL="0002-use-aws.html"];
    _1 -> _2 [style="dotted", weight=1];
    _3 [label="3. Use Azure"; URL="0003-use-azure.html"];
    _2 -> _3 [style="dotted", weight=1];
    _4 [label="4. Use Region UK South and UK West"; URL="0004-use-region-uk-south-and-uk-west.html"];
    _3 -> _4 [style="dotted", weight=1];
    _5 [label="5. Use West Europe region instead of UK West region"; URL="0005-use-west-europe-region-instead-of-uk-west-region.html"];
    _4 -> _5 [style="dotted", weight=1];
  }
  _3 -> _2 [label="Supercedes", weight=0]
  _3 -> _5 [label="Influences", weight=0]
  _4 -> _3 [label="Dependency", weight=0]
  _5 -> _4 [label="Partially obsoletes", weight=0]
  _5 -> _3 [label="Dependency", weight=0]
}

To make the graphviz part work, you’ll need to install graphviz, which is just an apt get away.

Any caveats?

adr-tools is not actively maintained. I’ve contacted the author, about seeing if I can help out with the maintenance, but… we’ll see, and given some fairly high profile malware takeovers of projects like this sort of thing on Github, Docker, NPM, and more… I can see why there might be some reluctance to consider it! Also, I’m an unknown entity, I’ve just dropped in on the project and offered to help, with no previous exposure to the lead dev or the project… so, we’ll see. Worst case, I’ll fork it!

Working with this also requires an understanding of markdown files, and why these might be a useful document format for records like this. There was a PR submitted to support multiple file formats (like asciidoc and rst) but these were not approved by the author.

There is no current intention to support languages other than English. The tool is hard-coded to look for strings like “status” and “superceded” which is hard. Part of the reason I raised the PRs I did was to let me fix some of these sorts of issues. Again, we’ll see what happens.

Lastly, it can be overwhelming to see a lot of documents in one place, particularly if they’re as granular as the documents I produced in this demo. If the project supported categories, or could be broken down into components (like doc/adr/networking and doc/adr/server_builds and doc/adr/applications) then this might help, but it’s not on the roadmap right now!

Late edit 2021-01-25: If you don’t think these templates have enough context or content, there are lots of others listed on Joel Parker Henderson’s repo of examples and templates. If you want a python based viewer of ADR records, take a look at adr-viewer.

Featured image is β€œBlueprints” by β€œCameron Degelia” on Flickr and is released under a CC-BY license.

"Salmon leaping" by "openpad" on Flickr

Using public #git sources in private projects

The last post I made was about using submodules to work with code that is being developed, either in isolation from other aspects of a project, or so components can be reused without requiring lots of copy-and-paste activities. It was inspired by a question from a colleague. After asking a few more questions, it turns out that may be what that colleague needed was to consume code from other repositories and store them in their own project.

In this case, I’ve created two repositories, both on GitHub (which will both be removed by the time this post is published) called JonTheNiceGuy/Git_Demo (the “upstream”, open source project) and JonTheNiceGuy-Inc/Git_Demo (the private project, referred to as “mine”).

Getting the “Open Source” project started

Here we have a simple repository, showing the README file for the project (which is likely, in the real world, to show what license that code has been released under, some explaination on what it’s for, etc.) and the actual data source. In this demo, the data source is a series of numbers, showing the decimal number in the first column, the binary representation of that number in the second column, and the hexedecimal representation in the third column.

Our “upstream” repository, showing the README.md file and the data source we want to use.
The data source itself. Note, I forgot to take a screen shot of this file, so I’ve had to “go back to a previous commit” to collect this particular image.

Elsewhere in the world, a private project has started! It’s going to use this data source as some element of this project, and to ensure that the code they’re relying on doesn’t go away, they create their own repository which this code will go into.

Preparing the private project

If both repositories are using GitHub, or if both repositories are using GitLab, then you should be able to “just” Fork the repository, using the “Fork” button in the top right corner:

The “Fork” button

And then select the organisation or account to place the forked repo into.

A list of potential targets to fork the repository into. Your view may differ if you are part of less organisations.

Gitlab has a similar workflow – they have a similar “fork” button, but the list of potential targets is different (but still works the same way).

Gitlab’s list of potential targets to fork the repository into.

Note that you can’t “easily” fork between different Version Control Services! To do something similar, you need to create a new repository in the target service, and then, run some commands to move the code over.

The screen you see immediately after you’ve created a new project – here I’ve created it in the “JonTheNiceGuy-Inc” Organisation. You can see the “quick setup” panel which has the URL to use for the repository.
Here we see the results of running five commands, which are: git clone <url> ; cd <target-dir> ; git remote rename origin upstream ; git remote add mine <url> ; git push –set-upstream mine main

If you’re using the command line method, here’s the commands you issue:

  • git clone http://service/user/repo – This command clones the repository from your service of choice to your local file system. It usually places it into the name of the repository you specified. In this case, “repo”, but in the above context (cloning from Git_Demo.git) it goes into “Git_Demo”. Note, HTTP(S) isn’t the only git transport, another common one is SSH, so if you prefer using SSH instead of HTTP, the URL in this case will be something like git@service:user/repo or service:user/repo. If you’re using submodules, however, I’d strongly recommend using HTTP(S) over SSH for at least the initial pull, as this is much easier for clients to navigate.
  • cd repo – Move into the directory where the cloned repository has been placed.
  • OPTIONAL: git remote rename origin upstream – Rename the remote source of the repository. By default, when you git clone or use git submodule add, the name of the remote resource is called “origin”. I prefer to give a descriptive name for my remote sources, so using “upstream” makes more sense to me. In later commands, I’ll use the remote name “upstream” again. If you don’t want to run this command, and leave the remote name as “origin”, you’ll just have to remember to change it back to “origin”.
  • git remote add mine http://new-service/user/repo – this adds a new remote source, to which you can push new commits, or pull code from your peers. Again, like in the git clone command above, you may use another URL format instead of HTTP(S). You may want to use a different name for the new remote, but again, I tend to prefer “mine” for anything I’m personally working on.
  • git push --set-upstream mine main – This sends the entire commit tree for the branch you’re currently on to your remote source.
Once we’ve run the git push, you can now see that the code has all been pushed to your private project.
Issuing a git log command, shows the current tip on the branch “main” in the “upstream” repository is equal to the current tip on the branch “main” in the “mine” repository, as well as the tip of the “main” repository locally.

Making your local changes

So, while you could just keep using just the upstream project’s code (and doing the above groundwork is good practice to keep you from putting yourself into the situation that the NPM world got into with “left-pad”). What’s more likely is that you want to make your own, local changes to this repository. I’ve done this in the past where I wanted to demonstrate a software build using a public machine image, but internally at work we used our own images. Using this method, I can consume the code I’ve created in public, and just update the assets we use at work.

In this example, let’s update that data file. I’ve added two new lines, “115” (and it’s binary/hex representations) and “132”. I can use the git diff command to confirm the changes I want to make – it’s all good!

Next, I stage the changes with git add, use git commit to write it to the branch, and git push to push it up to my repository. This is all fairly standard stuff in the Git world.

Here we make a change to the data source, confirm there is a difference, add and commit it, and then push it to our default branch (mine/main).

When I then check the git log, we see that there’s a divergence, between my local main branch and the upstream main branch. You could also use git log -p to see the exact code changes, if you wanted… but we know what’s changed already.

The git log, showing that we have a “local” change from the “upstream” source, and that we’ve pushed that local change to the “mine” source.

Bringing data from the upstream source

Oh joy! The upstream project (“JonTheNiceGuy” not “JonTheNiceGuy-Inc”) have updated their Git_Demo repository – they’ve had the audacity to add three new numbers – 9, 10 and 15 – to the data source.

The patch that was applied to this branch. We can check the difference here before we try to do anything with it! It’s something we want!

Well, actually we want to use that data, so let’s start bringing it in. We use the git pull command.

The git pull command, with the remote source (“upstream”) and the branch (“main”) to use.

Because this makes a change to a file that you’ve amended as part of your work, it can’t perform a “Fast forward” of these changes, so Git has to perform a merge commit. This means there’s a new commit in the log, so it’s clear that we’ve updated files because of this merge.

If there were a conflict in this file (which, fortunately, there isn’t!) you’d also be prompted to fix the merge conflicts too. This is a bit bigger than what I’m trying to explain, so instead, I’ll link to a tutorial by Atlassian on merge conflicts. You may also want to take a quick look at the rebasing page on the Git Project’s documentation site, and see whether this might have made your life easier in the case of a conflict!

Anyway, let’s use the default merge message.

The default message when performing a git pull where the change can’t be fast-forwarded.

Once the merge message is done, the merge completes. Yey!

We successfully merged our change, and it’s now part of our local tree

And to prove it, we can now see that we have all the changes from the upstream (commits starting 3b75eb, 8ad9ae, 8bdcae and the new one at a64de2) and our local changes (starting 02e40e).

Because we performed a merge, not a fast forward, our local branch is at a different commit than either of our remote sources – the commit starting 6f4db6 is on our local version, “upstream” is at a64de2 and “mine” is at 02e40e. So we need to fix at least our “mine/main” branch. We do this with a git push.

We do our git push here to get the code into our “mine/main” branch.

And now we can see the git log on our service.

The list of commits on Github for our “mine/main” branch.

And locally, we can see that the remote state has changed too. Let’s look at that git log again.

The result of the git log command on our local machine, showing the new position of the pointers for “upstream/main”, “mine/main” and the local “main” branches.

We can also look at the git blame on the service.

The git blame screen on GitHub, showing who made the various commits.

Or on our local machine.

git blame run locally, showing the commit reference, the author, the date and time of the commit, and the line number, followed by the line in question.

Featured image is β€œSalmon leaping” by β€œopenpad” on Flickr and is released under a CC-BY license.

"Submarine" by "NH53" on Flickr

Recursive Git Submodules

One of my colleagues asked today about using recursive git submodules. First, let’s quickly drill into what a Submodule is.

Git Submodules

A submodule is a separate git repository, attached to the git repository you’re working on via two “touch points” – a file in the root directory called .gitmodules, and, when checked out, the HEAD file in the .git directory.

When you clone a repository with a submodule attached, it creates the directory the submodule will be cloned into, but leave it empty, unless you either do git submodule update --init --recursive or, when you clone the repository initially, you can ask it to pull any recursive submodules, like this git clone https://your.vcs.example.org/someorg/somerepo.git --recursive.

Git stores the commit reference of the submodule (via a file in .git/modules/$SUBMODULE_NAME/HEAD which contains the commit reference). If you change a file in that submodule, it marks the path of the submodule as “dirty” (because you have an uncommitted change), and if you either commit that change, or pull an updated commit from the source repository, then it will mark the path of the submodule as having changed.

In other words, you can track two separate but linked parts of your code in the same tree, working on each in turn, and without impacting each other code base.

I’ve used this, mostly with Ansible playbooks, where I’ve consumed someone else’s role, like this:

My_Project
|
+- Roles
|  |
|  +- <SUBMODULE> someorg.some_role
|  +- <SUBMODULE> anotherorg.another_role
+- inventory
+- playbook.yml
+- .git
|  |
|  +- HEAD
|  +- modules
|  +- etc
+- .gitmodules

In .gitmodules the file looks like this:

[submodule "module1"]
 path = module1
 url = https://your.vcs.example.org/someorg/module1.git

Once you’ve checked out this submodule, you can do any normal operations in this submodule, like pulls, pushes, commits, tags, etc.

So, what happens when you want to nest this stuff?

Nesting Submodule Recursion

So, my colleague wanted to have files in three layers of directories. In this instance, I’ve simulated this by creating three directories, root, module1 and module2. Typically these would be pulled from their respective Git Service paths, like GitHub or GitLab, but here I’m just using everything on my local file system. Where, in the following screen shot, you see /tmp/ you could easily replace that with https://your.vcs.example.org/someorg/.

The output of running mkdir {root,module1,module2} ; cd root ; git init ; cd ../module1 ; git init ; cd ../module2 ; git init ; touch README.md ; git add README.md ; git commit -m 'Added README.md' ; cd ../module1 ; git submodule add /tmp/module2 module2 ; git commit -m 'Added module2' ; cd ../root ; git submodule add /tmp/module1 module1 ; git submodule update --init --recursive ; tree showing the resulting tree of submodules under the root directory.
The output of running mkdir {root,module1,module2} ; cd root ; git init ; cd ../module1 ; git init ; cd ../module2 ; git init ; touch README.md ; git add README.md ; git commit -m ‘Added README.md’ ; cd ../module1 ; git submodule add /tmp/module2 module2 ; git commit -m ‘Added module2’ ; cd ../root ; git submodule add /tmp/module1 module1 ; git submodule update –init –recursive ; tree showing the resulting tree of submodules under the root directory.

So, here, we’ve created these three paths (basically to initiate the repositories), added a basic commit to the furthest submodule (module2), then done a submodule add into the next furthest submodule (module1) and finally added that into the root tree.

Note, however, when you perform the submodule add it doesn’t automatically clone any submodules, and if you were to, from another machine, perform git clone https://your.vcs.example.org/someorg/root.git you wouldn’t get any of the submodules (neither module1 nor module2) without adding either --recursive to the clone command (like this: git clone --recursive https://your.vcs.example.org/someorg/root.git), or by running the follow-up command git submodule update --init --recursive.

Oh, and if any of these submodules are updated? You need to go in and pull those updates, and then commit that change, like this!

The workflow of pulling updates for each of the submodules, with git add, git commit, and git pull, also noting that when a module has been changed, it shows as having “new commits”.
And here we have the finish of the workflow, updating the other submodules. Note that some of these steps (probably the ones in the earlier image) are likely to have been performed by some other developer on another system, so having all the updates on one machine is pretty rare!

The only thing which isn’t in these submodules is if you’ve done a git clone of the root repo (using the terms from the above screen images), the submodules won’t be using the “master” branch (or a particular “tag” or “branch hame”, for that matter), but will instead be using the commit reference. If you wanted to switch to a specific branch or tag, then you’d need to issue the command git checkout some_remote/some_branch or git checkout master instead of (in the above screen captures) git pull.

If you have any questions or issues with this post, please either add a comment, or contact me via one of the methods at the top or side of this page!

Featured image is β€œSubmarine” by β€œNH53” on Flickr and is released under a CC-BY license.

"Kelvin Test" by "Eelke" on Flickr

In Ansible, determine the type of a value, and casting those values to other types

TL;DR? It’s possible to work out what type of variable you’re working with in Ansible. The in-built filters don’t always do quite what you’re expecting. Jump to the “In Summary” heading for my suggestions.

LATE EDIT: 2021-05-23 After raising a question in #ansible on Freenode, flowerysong noticed that my truth table around mappings, iterables and strings was wrong. I’ve amended the table accordingly, and have added a further note below the table.

One of the things I end up doing quite a bit with Ansible is value manipulation. I know it’s not really normal, but… well, I like rewriting values from one type of a thing to the next type of a thing.

For example, I like taking a value that I don’t know if it’s a list or a string, and passing that to an argument that expects a list.

Doing it wrong, getting it better

Until recently, I’d do that like this:

- debug:
    msg: |-
      {
        {%- if value | type_debug == "string" or value | type_debug == "AnsibleUnicode" -%}
           "string": "{{ value }}"
        {%- elif value | type_debug == "dict" or value | type_debug == "ansible_mapping" -%}
          "dict": {{ value }}
        {%- elif value | type_debug == "list" -%}
          "list": {{ value }}
        {%- else -%}
          "other": "{{ value }}"
        {%- endif -%}
      }

But, following finding this gist, I now know I can do this:

- debug:
    msg: |-
      {
        {%- if value is string -%}
           "string": "{{ value }}"
        {%- elif value is mapping -%}
          "dict": {{ value }}
        {%- elif value is iterable -%}
          "list": {{ value }}
        {%- else -%}
          "other": "{{ value }}"
        {%- endif -%}
      }

So, how would I use this, given the context of what I was saying before?

- assert:
    that:
    - value is string
    - value is not mapping
    - value is iterable
- some_module:
    some_arg: |-
      {%- if value is string -%}
        ["{{ value }}"]
      {%- else -%}
        {{ value }}
      {%- endif -%}

More details on finding a type

Why in this order? Well, because of how values are stored in Ansible, the following states are true:

⬇️Type \ ➑️Checkis iterableis mappingis sequenceis string
a_dict (e.g. {})βœ”οΈβœ”οΈβœ”οΈβŒ
a_list (e.g. [])βœ”οΈβŒβœ”οΈβŒ
a_string (e.g. “”)βœ”οΈβŒβœ”οΈβœ”οΈ
A comparison between value types

So, if you were to check for is iterable first, you might match on a_list or a_dict instead of a_string, but string can only match on a_string. Once you know it can’t be a string, you can check whether something is mapping – again, because a mapping can only match a_dict, but it can’t match a_list or a_string. Once you know it’s not that, you can check for either is iterable or is sequence because both of these match a_string, a_dict and a_list.

LATE EDIT: 2021-05-23 Note that a prior revision of this table and it’s following paragraph showed “is_mapping” as true for a_string. This is not correct, and has been fixed, both in the table and the paragraph.

Likewise, if you wanted to check whether a_float and an_integer is number and not is string, you can check these:

⬇️Type \ ➑️Checkis floatis integeris iterableis mappingis numberis sequenceis string
a_floatβœ”οΈβŒβŒβŒβœ”οΈβŒβŒ
an_integerβŒβœ”οΈβŒβŒβœ”οΈβŒβŒ
A comparison between types of numbers

So again, a_float and an_integer don’t match is string, is mapping or is iterable, but they both match is number and they each match their respective is float and is integer checks.

How about each of those (a_float and an_integer) wrapped in quotes, making them a string? What happens then?

⬇️Type \ ➑️Checkis floatis integeris iterableis mappingis numberis sequenceis string
a_float_as_stringβŒβŒβœ”οΈβŒβŒβœ”οΈβœ”οΈ
an_integer_as_stringβŒβŒβœ”οΈβŒβŒβœ”οΈβœ”οΈ
A comparison between types of numbers when held as a string

This is somewhat interesting, because they look like a number, but they’re actually “just” a string. So, now you need to do some comparisons to make them look like numbers again to check if they’re numbers.

Changing the type of a string

What happens if you cast the values? Casting means to convert from one type of value (e.g. string) into another (e.g. float) and to do that, Ansible has three filters we can use, float, int and string. You can’t cast to a dict or a list, but you can use dict2items and items2dict (more on those later). So let’s start with casting our group of a_ and an_ items from above. Here’s a list of values I want to use:

---
- hosts: localhost
  gather_facts: no
  vars:
    an_int: 1
    a_float: 1.1
    a_string: "string"
    an_int_as_string: "1"
    a_float_as_string: "1.1"
    a_list:
      - item1
    a_dict:
      key1: value1

With each of these values, I returned the value as Ansible knows it, what happens when you do {{ value | float }} to cast it as a float, as an integer by doing {{ value | int }} and as a string {{ value | string }}. Some of these results are interesting. Note that where you see u'some value' means that Python converted that string to a Unicode string.

⬇️Value \ ➑️Castvaluevalue when cast as floatvalue when cast as integervalue when cast as string
a_dict{“key1”: “value1”}0.00“{u’key1′: u’value1′}”
a_float1.11.11“1.1”
a_float_as_string“1.1”1.11“1.1”
a_list[“item1”]0.00“[u’item1′]”
a_string“string”0.00“string”
an_int111“1”
an_int_as_string“1”11“1”
Casting between value types

So, what does this mean for us? Well, not a great deal, aside from to note that you can “force” a number to be a string, or a string which is “just” a number wrapped in quotes can be forced into being a number again.

Oh, and casting dicts to lists and back again? This one is actually pretty clearly documented in the current set of documentation (as at 2.9 at least!)

Checking for miscast values

How about if I want to know whether a value I think might be a float stored as a string, how can I check that?

{{ vars[var] | float | string == vars[var] | string }}

What is this? If I cast a value that I think might be a float, to a float, and then turn both the cast value and the original into a string, do they match? If I’ve got a string or an integer, then I’ll get a false, but if I have actually got a float, then I’ll get true. Likewise for casting an integer. Let’s see what that table looks like:

⬇️Type \ ➑️Checkvalue when cast as floatvalue when cast as integervalue when cast as string
a_floatβœ”οΈβŒβœ”οΈ
a_float_as_stringβœ”οΈβŒβœ”οΈ
an_integerβŒβœ”οΈβœ”οΈ
an_integer_as_stringβŒβœ”οΈβœ”οΈ
A comparison between types of numbers when cast to a string

So this shows us the values we were after – even if you’ve got a float (or an integer) stored as a string, by doing some careful casting, you can confirm they’re of the type you wanted… and then you can pass them through the right filter to use them in your playbooks!

Booleans

Last thing to check – boolean values – “True” or “False“. There’s a bit of confusion here, as a “boolean” can be: true or false, yes or no, 1 or 0, however, is true and True and TRUE the same? How about false, False and FALSE? Let’s take a look!

⬇️Value \ ➑️Checktype_debug is booleanis numberis iterableis mappingis stringvalue when cast as boolvalue when cast as stringvalue when cast as integer
yesboolβœ”οΈβœ”οΈβŒβŒβŒTrueTrue1
YesAnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈFalseYes0
YESAnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈFalseYES0
“yes”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈTrueyes0
“Yes”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈTrueYes0
“YES”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈTrueYES0
trueboolβœ”οΈβœ”οΈβŒβŒβŒTrueTrue1
Trueboolβœ”οΈβœ”οΈβŒβŒβŒTrueTrue1
TRUEboolβœ”οΈβœ”οΈβŒβŒβŒTrueTrue1
“true”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈTruetrue0
“True”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈTrueTrue0
“TRUE”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈTrueTRUE0
1intβŒβœ”οΈβŒβŒβŒTrue11
“1”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈTrue11
noboolβœ”οΈβœ”οΈβŒβŒβŒFalseFalse0
Noboolβœ”οΈβœ”οΈβŒβŒβŒFalseFalse0
NOboolβœ”οΈβœ”οΈβŒβŒβŒFalseFalse0
“no”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈFalseno0
“No”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈFalseNo0
“NO”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈFalseNO0
falseboolβœ”οΈβœ”οΈβŒβŒβŒFalseFalse0
Falseboolβœ”οΈβœ”οΈβŒβŒβŒFalseFalse0
FALSEboolβœ”οΈβœ”οΈβŒβŒβŒFalseFalse0
“false”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈFalsefalse0
“False”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈFalseFalse0
“FALSE”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈFalseFALSE0
0intβŒβœ”οΈβŒβŒβŒFalse00
“0”AnsibleUnicodeβŒβŒβœ”οΈβŒβœ”οΈFalse00
Comparisons between various stylings of boolean representations

So, the stand out thing for me here is that while all the permutations of string values of the boolean representations (those wrapped in quotes, like this: "yes") are treated as strings, and shouldn’t be considered as “boolean” (unless you cast for it explicitly!), and all non-string versions of true, false, and no are considered to be boolean, yes, Yes and YES are treated differently, depending on case. So, what would I do?

In summary

  • Consistently use no or yes, true or false in lower case to indicate a boolean value. Don’t use 1 or 0 unless you have to.
  • If you’re checking that you’re working with a string, a list or a dict, check in the order string (using is string), dict (using is mapping) and then list (using is sequence or is iterable)
  • Checking for numbers that are stored as strings? Cast your string through the type check for that number, like this: {% if value | float | string == value | string %}{{ value | float }}{% elif value | int | string == value | string %}{{ value | int }}{% else %}{{ value }}{% endif %}
  • Try not to use type_debug unless you really can’t find any other way. These values will change between versions, and this caused me a lot of issues with a large codebase I was working on a while ago!

Run these tests yourself!

Want to run these tests yourself? Here’s the code I ran (also available in a Gist on GitHub), using Ansible 2.9.10.

---
- hosts: localhost
  gather_facts: no
  vars:
    an_int: 1
    a_float: 1.1
    a_string: "string"
    an_int_as_string: "1"
    a_float_as_string: "1.1"
    a_list:
      - item1
    a_dict:
      key1: value1
  tasks:
    - debug:
        msg: |
          {
          {% for var in ["an_int", "an_int_as_string","a_float", "a_float_as_string","a_string","a_list","a_dict"] %}
            "{{ var }}": {
              "type_debug": "{{ vars[var] | type_debug }}",
              "value": "{{ vars[var] }}",
              "is float": "{{ vars[var] is float }}",
              "is integer": "{{ vars[var] is integer }}",
              "is iterable": "{{ vars[var] is iterable }}",
              "is mapping": "{{ vars[var] is mapping }}",
              "is number": "{{ vars[var] is number }}",
              "is sequence": "{{ vars[var] is sequence }}",
              "is string": "{{ vars[var] is string }}",
              "value cast as float": "{{ vars[var] | float }}",
              "value cast as integer": "{{ vars[var] | int }}",
              "value cast as string": "{{ vars[var] | string }}",
              "is same when cast to float": "{{ vars[var] | float | string == vars[var] | string }}",
              "is same when cast to integer": "{{ vars[var] | int | string == vars[var] | string }}",
              "is same when cast to string": "{{ vars[var] | string == vars[var] | string }}",
            },
          {% endfor %}
          }
---
- hosts: localhost
  gather_facts: false
  vars:
    # true, True, TRUE, "true", "True", "TRUE"
    a_true: true
    a_true_initial_caps: True
    a_true_caps: TRUE
    a_string_true: "true"
    a_string_true_initial_caps: "True"
    a_string_true_caps: "TRUE"
    # yes, Yes, YES, "yes", "Yes", "YES"
    a_yes: yes
    a_yes_initial_caps: Tes
    a_yes_caps: TES
    a_string_yes: "yes"
    a_string_yes_initial_caps: "Yes"
    a_string_yes_caps: "Yes"
    # 1, "1"
    a_1: 1
    a_string_1: "1"
    # false, False, FALSE, "false", "False", "FALSE"
    a_false: false
    a_false_initial_caps: False
    a_false_caps: FALSE
    a_string_false: "false"
    a_string_false_initial_caps: "False"
    a_string_false_caps: "FALSE"
    # no, No, NO, "no", "No", "NO"
    a_no: no
    a_no_initial_caps: No
    a_no_caps: NO
    a_string_no: "no"
    a_string_no_initial_caps: "No"
    a_string_no_caps: "NO"
    # 0, "0"
    a_0: 0
    a_string_0: "0"
  tasks:
    - debug:
        msg: |
          {
          {% for var in ["a_true","a_true_initial_caps","a_true_caps","a_string_true","a_string_true_initial_caps","a_string_true_caps","a_yes","a_yes_initial_caps","a_yes_caps","a_string_yes","a_string_yes_initial_caps","a_string_yes_caps","a_1","a_string_1","a_false","a_false_initial_caps","a_false_caps","a_string_false","a_string_false_initial_caps","a_string_false_caps","a_no","a_no_initial_caps","a_no_caps","a_string_no","a_string_no_initial_caps","a_string_no_caps","a_0","a_string_0"] %}
            "{{ var }}": {
              "type_debug": "{{ vars[var] | type_debug }}",
              "value": "{{ vars[var] }}",
              "is float": "{{ vars[var] is float }}",
              "is integer": "{{ vars[var] is integer }}",
              "is iterable": "{{ vars[var] is iterable }}",
              "is mapping": "{{ vars[var] is mapping }}",
              "is number": "{{ vars[var] is number }}",
              "is sequence": "{{ vars[var] is sequence }}",
              "is string": "{{ vars[var] is string }}",
              "is bool": "{{ vars[var] is boolean }}",
              "value cast as float": "{{ vars[var] | float }}",
              "value cast as integer": "{{ vars[var] | int }}",
              "value cast as string": "{{ vars[var] | string }}",
              "value cast as bool": "{{ vars[var] | bool }}",
              "is same when cast to float": "{{ vars[var] | float | string == vars[var] | string }}",
              "is same when cast to integer": "{{ vars[var] | int | string == vars[var] | string }}",
              "is same when cast to string": "{{ vars[var] | string == vars[var] | string }}",
              "is same when cast to bool": "{{ vars[var] | bool | string == vars[var] | string }}",
            },
          {% endfor %}
          }

Featured image is β€œKelvin Test” by β€œEelke” on Flickr and is released under a CC-BY license.