"Family" by "Ivan" on Flickr

Debian on Docker using Vagrant

I want to use Vagrant-Docker to try standing up some environments. There’s no reasonable justification, it’s just a thing I wanted to do. Normally, I’d go into this long and rambling story about why… but on this occasion, the reason was “Because it’s possible”…

TL;DR?: Get the code from the repo and enjoy 😁

Installing Docker

On Ubuntu you can install Docker following the instructions on the Docker Install Page, which includes a convenience script (that runs all the commands you need), if you want to use it. Similar instructions for Debian, CentOS and Fedora exist.

On Windows or Mac there are downloads you can get from the Docker Hub. The Windows Version requires WSL2. I don’t have a Mac, so I don’t know what the requirements are there! Installing WSL2 has a whole host of extra steps that I can’t really do justice to. See this Microsoft article for details.

Installing Vagrant

On Debian and Ubuntu you can add the HashiCorp Apt Repo and then install Vagrant, using these commands:

curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo apt-key add -
sudo apt-add-repository "deb [arch=amd64] https://apt.releases.hashicorp.com $(lsb_release -cs) main"
sudo apt install vagrant

There are similar instructions for RHEL, CentOS and Fedora users there too.

Windows and Mac users will have to get the application from the download page.

Creating your Dockerfile

A Dockerfile is a simple text file which has a series of line prefixes which instruct the Docker image processor to add certain instructions to the Docker Image. I found two pages which helped me with what to add for this; “Ansible. Docker. Vagrant. Bringing together” and the git repo “AkihiroSuda/containerized-systemd“.

You see, while a Dockerfile is great at starting single binary files or scripts, it’s not very good at running SystemD… and I needed SystemD to be able to run the SSH service that Vagrant requires, and to also run the scripts and commands I needed for the image I wanted to build…

Sooooo…. here’s the Dockerfile I created:

# Based on https://vtorosyan.github.io/ansible-docker-vagrant/
# and https://github.com/AkihiroSuda/containerized-systemd/

FROM debian:buster AS debian_with_systemd

# This stuff enables SystemD on Debian based systems
STOPSIGNAL SIGRTMIN+3
RUN DEBIAN_FRONTEND=noninteractive apt update && DEBIAN_FRONTEND=noninteractive apt install -y --no-install-recommends systemd systemd-sysv dbus dbus-user-session
COPY docker-entrypoint.sh /
RUN chmod 755 /docker-entrypoint.sh
ENTRYPOINT [ "/docker-entrypoint.sh" ]
CMD [ "/bin/bash" ]

# This part installs an SSH Server (required for Vagrant)
RUN DEBIAN_FRONTEND=noninteractive apt install -y sudo openssh-server
RUN mkdir /var/run/sshd
#    We enable SSH here, but don't start it with "now" as the build stage doesn't run anything long-lived.
RUN systemctl enable ssh
EXPOSE 22

# This part creates the vagrant user, sets the password to "vagrant", adds the insecure key and sets up password-less sudo.
RUN useradd -G sudo -m -U -s /bin/bash vagrant
#    chpasswd takes a colon delimited list of username/password pairs.
RUN echo 'vagrant:vagrant' | chpasswd
RUN mkdir -m 700 /home/vagrant/.ssh
# This key from https://github.com/hashicorp/vagrant/tree/main/keys. It will be replaced on first run.
RUN echo 'ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA6NF8iallvQVp22WDkTkyrtvp9eWW6A8YVr+kz4TjGYe7gHzIw+niNltGEFHzD8+v1I2YJ6oXevct1YeS0o9HZyN1Q9qgCgzUFtdOKLv6IedplqoPkcmF0aYet2PkEDo3MlTBckFXPITAMzF8dJSIFo9D8HfdOV0IAdx4O7PtixWKn5y2hMNG0zQPyUecp4pzC6kivAIhyfHilFR61RGL+GPXQ2MWZWFYbAGjyiYJnAmCP3NOTd0jMZEnDkbUvxhMmBYSdETk1rRgm+R4LOzFUGaHqHDLKLX+FIPKcF96hrucXzcWyLbIbEgE98OHlnVYCzRdK8jlqm8tehUc9c9WhQ== vagrant insecure public key' > /home/vagrant/.ssh/authorized_keys
RUN chmod 600 /home/vagrant/.ssh/authorized_keys
RUN chown -R vagrant:vagrant /home/vagrant
RUN echo 'vagrant ALL=(ALL:ALL) NOPASSWD:ALL' >> /etc/sudoers

This Dockerfile calls out to a separate script, called docker-entrypoint.sh, taken verbatim from AkihiroSuda’s repo, so here’s that file:

#!/bin/bash
set -ex
container=docker
export container

if [ $# -eq 0 ]; then
	echo >&2 'ERROR: No command specified. You probably want to run `journalctl -f`, or maybe `bash`?'
	exit 1
fi

if [ ! -t 0 ]; then
	echo >&2 'ERROR: TTY needs to be enabled (`docker run -t ...`).'
	exit 1
fi

env >/etc/docker-entrypoint-env

cat >/etc/systemd/system/docker-entrypoint.target <<EOF
[Unit]
Description=the target for docker-entrypoint.service
Requires=docker-entrypoint.service systemd-logind.service systemd-user-sessions.service
EOF
cat /etc/systemd/system/docker-entrypoint.target

quoted_args="$(printf " %q" "${@}")"
echo "${quoted_args}" >/etc/docker-entrypoint-cmd
cat /etc/docker-entrypoint-cmd

cat >/etc/systemd/system/docker-entrypoint.service <<EOF
[Unit]
Description=docker-entrypoint.service

[Service]
ExecStart=/bin/bash -exc "source /etc/docker-entrypoint-cmd"
# EXIT_STATUS is either an exit code integer or a signal name string, see systemd.exec(5)
ExecStopPost=/bin/bash -ec "if echo \${EXIT_STATUS} | grep [A-Z] > /dev/null; then echo >&2 \"got signal \${EXIT_STATUS}\"; systemctl exit \$(( 128 + \$( kill -l \${EXIT_STATUS} ) )); else systemctl exit \${EXIT_STATUS}; fi"
StandardInput=tty-force
StandardOutput=inherit
StandardError=inherit
WorkingDirectory=$(pwd)
EnvironmentFile=/etc/docker-entrypoint-env

[Install]
WantedBy=multi-user.target
EOF
cat /etc/systemd/system/docker-entrypoint.service

systemctl mask systemd-firstboot.service systemd-udevd.service
systemctl unmask systemd-logind
systemctl enable docker-entrypoint.service

systemd=
if [ -x /lib/systemd/systemd ]; then
	systemd=/lib/systemd/systemd
elif [ -x /usr/lib/systemd/systemd ]; then
	systemd=/usr/lib/systemd/systemd
elif [ -x /sbin/init ]; then
	systemd=/sbin/init
else
	echo >&2 'ERROR: systemd is not installed'
	exit 1
fi
systemd_args="--show-status=false --unit=multi-user.target"
echo "$0: starting $systemd $systemd_args"
exec $systemd $systemd_args

Now, if you were to run this straight in Docker, it will fail, because you must pass certain flags to Docker to get this to run. These flags are:

  • -t : pass a “TTY” to the shell
  • --tmpfs /tmp : Create a temporary filesystem in /tmp
  • --tmpfs /run : Create another temporary filesystem in /run
  • --tmpfs /run/lock : Apparently having a tmpfs in /run isn’t enough – you ALSO need one in /run/lock
  • -v /sys/fs/cgroup:/sys/fs/cgroup:ro : Mount the CGroup kernel configuration values into the container

(I found these flags via a RedHat blog post, and a Podman issue on Github.)

So, how would this look, if you were to try and run it?

docker exec -t --tmpfs /tmp --tmpfs /run --tmpfs /run/lock -v /sys/fs/cgroup:/sys/fs/cgroup:ro YourImage

Blimey, what a long set of text! Perhaps we could hide that behind something a bit more legible? Enter Vagrant.

Creating your Vagrantfile

Vagrant is an abstraction tool, designed to hide complicated virtualisation scripts into a simple command. In this case, we’re hiding a containerisation script into a simple command.

Like with the Dockerfile, I made extensive use of the two pages I mentioned before, as well as the two pages to get the flags to run this.

# Based on https://vtorosyan.github.io/ansible-docker-vagrant/
# and https://github.com/AkihiroSuda/containerized-systemd/
# and https://developers.redhat.com/blog/2016/09/13/running-systemd-in-a-non-privileged-container/
# with tweaks indicated by https://github.com/containers/podman/issues/3295
ENV['VAGRANT_DEFAULT_PROVIDER'] = 'docker'
Vagrant.configure("2") do |config|
  config.vm.provider "docker" do |d|
    d.build_dir       = "."
    d.has_ssh         = true
    d.remains_running = false
    d.create_args     = ['--tmpfs', '/tmp', '--tmpfs', '/run', '--tmpfs', '/run/lock', '-v', '/sys/fs/cgroup:/sys/fs/cgroup:ro', '-t']
  end
end

If you create that file, and run vagrant up you’ll get a working Vagrant boot… But if you try and execute any shell scripts, they’ll fail to run, as the they aren’t passed in with execute permissions… so I want to use Ansible to execute things, as these don’t require execute permissions on the /vagrant directory (also, as the thing I’m building in there requires Ansible… so it’s helpful either way 😁)

Executing Ansible scripts

Ansible still expects to find python in /usr/bin/python but current systems don’t make the symlink to /usr/bin/python3, as python was typically a symlink to /usr/bin/python2… and also I wanted to put the PPA for Ansible in the sources, which is what the Ansible team recommend in their documentation. I’ve done this as part of the Dockerfile, as again, I can’t run scripts from Vagrant. So, here’s the addition I made to the Dockerfile.

FROM debian_with_systemd AS debian_with_systemd_and_ansible
RUN apt install -y gnupg2 lsb-release software-properties-common
RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 93C4A3FD7BB9C367
RUN add-apt-repository "deb http://ppa.launchpad.net/ansible/ansible/ubuntu trusty main"
RUN apt install -y ansible
# Yes, I know. Trusty? On Debian Buster?? But, that's what the Ansible Docs say!

In the Vagrantfile, I’ve added this block:

config.vm.provision "ansible_local" do |ansible|
  ansible.playbook = "test.yml"
end

And I created a test.yml, which looks like this:

---
- hosts: all
  tasks:
  - debug:
      msg: "Hello from Docker"

Running it

So how does this look on Windows when I run it?

PS C:\Dev\VagrantDockerBuster> vagrant up
==> default: Creating and configuring docker networks...
==> default: Building the container from a Dockerfile...
<SNIP A LOAD OF DOCKER STUFF>
    default: #20 DONE 0.1s
    default:
    default: Image: 190ffdeaeed0b7ed206097e6c1d4b5cc796a428700c9bd3e27eedacce47fb63b
==> default: Creating the container...
    default:   Name: 2021-02-13DockerBusterWithSSH_default_1613469604
    default:  Image: 190ffdeaeed0b7ed206097e6c1d4b5cc796a428700c9bd3e27eedacce47fb63b
    default: Volume: C:/Users/SPRIGGSJ/OneDrive - FUJITSU/Documents/95 My Projects/2021-02-13 Docker Buster With SSH:/vagrant
    default:   Port: 127.0.0.1:2222:22
    default:
    default: Container created: b64ed264d8949b12
==> default: Enabling network interfaces...
==> default: Starting container...
==> 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
    default:
    default: Vagrant insecure key detected. Vagrant will automatically replace
    default: this with a newly generated keypair for better security.
    default:
    default: Inserting generated public key within guest...
==> default: Machine booted and ready!
==> default: Running provisioner: ansible_local...
    default: Running ansible-playbook...

PLAY [all] *********************************************************************

TASK [Gathering Facts] *********************************************************
[WARNING]: Platform linux on host default is using the discovered Python
interpreter at /usr/bin/python, but future installation of another Python
interpreter could change this. See https://docs.ansible.com/ansible/2.9/referen
ce_appendices/interpreter_discovery.html for more information.
ok: [default]

TASK [debug] *******************************************************************
ok: [default] => {
    "msg": "Hello from Docker"
}

PLAY RECAP *********************************************************************
default                    : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

PS C:\Dev\VagrantDockerBuster>

And on Linux?

Bringing machine 'default' up with 'docker' provider...
==> default: Creating and configuring docker networks...
==> default: Building the container from a Dockerfile...
<SNIP A LOAD OF DOCKER STUFF>
    default: Removing intermediate container e56bed4f7be9
    default:  ---> cef749c205bf
    default: Successfully built cef749c205bf
    default:
    default: Image: cef749c205bf
==> default: Creating the container...
    default:   Name: 2021-02-13DockerBusterWithSSH_default_1613470091
    default:  Image: cef749c205bf
    default: Volume: /home/spriggsj/Projects/2021-02-13 Docker Buster With SSH:/vagrant
    default:   Port: 127.0.0.1:2222:22
    default:
    default: Container created: 3fe46b02d7ad10ab
==> default: Enabling network interfaces...
==> default: Starting container...
==> 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
    default:
    default: Vagrant insecure key detected. Vagrant will automatically replace
    default: this with a newly generated keypair for better security.
    default:
    default: Inserting generated public key within guest...
    default: Removing insecure key from the guest if it's present...
    default: Key inserted! Disconnecting and reconnecting using new SSH key...
==> default: Machine booted and ready!
==> default: Running provisioner: ansible_local...
    default: Running ansible-playbook...

PLAY [all] *********************************************************************

TASK [Gathering Facts] *********************************************************
[WARNING]: Platform linux on host default is using the discovered Python
interpreter at /usr/bin/python, but future installation of another Python
interpreter could change this. See https://docs.ansible.com/ansible/2.9/referen
ce_appendices/interpreter_discovery.html for more information.
ok: [default]

TASK [debug] *******************************************************************
ok: [default] => {
    "msg": "Hello from Docker"
}

PLAY RECAP *********************************************************************
default                    : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

So, if you’re crazy and want to do Vagrant using Docker with Debian Buster and Ansible, this is how to do it. I don’t know how much I’m likely to be using this in the future, but if you use it, let me know what you’re doing with it! πŸ˜€

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

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