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https://github.com/mhutter/ansible-docker-systemd-service

Ansible role for creating Systemd services for docker containers
https://github.com/mhutter/ansible-docker-systemd-service

ansible docker systemd

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Ansible role for creating Systemd services for docker containers

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# Docker role `mhutter.docker-systemd-service`



Generic role for creating systemd services to manage docker containers.



## Example



Example of a Systemd unit for your app "myapp" that links to an already existing container "mysql":



```yaml

- name: Start WebApp

  include_role:

    name: mhutter.docker-systemd-service

  vars:

    container_name: myapp

    container_image: myapp:latest

    container_links: ["mysql"]

    container_volumes:

      - "/data/uploads:/data/uploads"

    container_ports:

      - "3000:3000"

    container_hosts:

      - "host.docker.internal:host-gateway"

    container_env:

      MYSQL_ROOT_PASSWORD: "{{ mysql_root_pw }}"

    container_labels:

      - "traefik.enable=true"

```



This will create:



- A file containing the env vars (either `/etc/sysconfig/myapp` or `/etc/default/myapp`).

- A systemd unit which starts and stops the container. The unit will be called `_container.service` to avoid name clashes.



### Role variables



- `container_name` (**required**) - name of the container



#### Docker container specifics



- `container_image` (**required**) - Docker image the service uses

- `container_args` - arbitrary list of arguments to the `docker run` command as a string

- `container_cmd` (default: _[]_) - optional list of commands to the container run command (the part after the image name)

- `container_env` - key/value pairs of ENV vars that need to be present

- `container_volumes` (default: _[]_) - List of `-v` arguments

- `container_host_network` (default: _false_) - Whether the host network should be used

- `container_ports` (default: _[]_) - List of `-p` arguments

- `container_hosts` (default: _[]_) - List of `--add-host` arguments

- `container_links` (default: _[]_) - List of `--link` arguments

- `container_labels` (default: _[]_) - List of `-l` arguments

- `container_docker_pull` (default: _yes_) - whether the docker image should be pulled

- `container_docker_pull_force_source` (default: _yes_) - whether the docker image pull should be executed at every time (see [`docker_image.force_source`](https://docs.ansible.com/ansible/latest/collections/community/docker/docker_image_module.html#parameter-force_source))

- `container_cap_add` (default _[]_) - List of capabilities to add

- `container_cap_drop` (default _{}_) - List of capabilities to drop

- `container_network` (default _""_) - [Network settings](https://docs.docker.com/engine/reference/run/#network-settings)

- `container_user` (default _""_) - [User settings](https://docs.docker.com/engine/reference/run/#user)

- `container_hostname` (default _""_) - Container host name: `--hostname` flag

- `container_devices` (default _[]_) - List of devices to add

- `container_privileged` (default _false_) - Whether the container should be privileged

- `container_start_post` - Optional command to be run by systemd after the container has started



#### Systemd service specifics



- `service_enabled` (default: _yes_) - whether the service should be enabled

- `service_masked` (default: _no_) - whether the service should be masked

- `service_state` (default: _started_) - state the service should be in - set to

  `absent` to remove the service.

- `service_restart` (default: _yes_) - whether the service should be restarted on changes

- `service_name` (default: `_container`) - name of the systemd service

- `service_systemd_options` (default: _[]_) - Extra options to include in systemd service file

- `service_systemd_unit_options`: (default `{"After": "docker.service", "PartOf": "docker.service", "Requires": "docker.service"}`), key/value defining the content of the `[Unit]` service section.



## Installation



This role requires the [docker python module](https://pypi.org/project/docker/). Install it with `pip3 install docker` or `apt install python3-docker` (or drop the `3` for python 2.x).



Put this in your `requirements.yml`:



```yml

- role: mhutter.docker-systemd-service

```



and run `ansible-galaxy install -r requirements.yml`.



## Gotchas



- When the unit or env file is changed, systemd gets reloaded but existing containers are NOT restarted.

- Make sure to quote values for `container_ports`, `container_hosts`, `container_volumes` and so on, especially if they contain colons (`:`). Otherwise YAML will interpret them as hashes/maps and ansible will throw up.



## About orchestrating Docker containers using systemd.



The concept behind this is to define `systemd` units for every docker container. This has some benefits:



- `systemd` is a well-known interface

- all services are controllable via the same tool (`systemctl`)

- all logs are accessible via the same tool (`journalctl`)

- dependencies can be defined

- startup behaviour can be defined

- by correctly defining the unit (see below), we can ensure we always have a clean container.



Here is an example `myapp_container.service` unit file (about what's produced by above code):



    [Unit]

    # define dependencies

    After=docker.service

    PartOf=docker.service

    Requires=docker.service



    [Service]

    # Load ENV vars from a file. Note that this env vars will only be

    # accessible in the context of the Exec* commands, and not within the

    # container itself. To make env-vars accessible within the Container, we use

    # the `--env-file` flag for the `docker run` command.

    EnvironmentFile=/etc/sysconfig/myapp



    # Even though we explicitly run the container using the `--rm` flag, there

    # may be leftover containers (eg. after a system-, docker- or app-crash).

    # Starting a container with an existing name will always fail.



    ExecStartPre=-/usr/bin/docker rm -f myapp



    # actually run the container.

    # `--name` to identify the container

    # `--rm` ensure the container is removed after stopping

    # `--env-file` make ENV vars accessible to app

    # `--link mysql` link to a container named `mysql`. The DB will then be

    #                accesible at `mysql:3306`

    # `-v` mount `/data/uploads` into the container

    # `-p 3000:3000` expose port 3000 on the network

    ExecStart=/usr/bin/docker run --name myapp --rm --env-file /etc/sysconfig/myapp --link mysql -v /data/uploads:/data/uploads -p 3000:3000 registry.cust.net/myapp/myapp:latest

    # note that there is no `--restart` parameter. This is because restarting

    # is taken care of by `systemd`.



    # Stop command.

    ExecStop=/usr/bin/docker stop myapp



    # Ensure log messages are correctly tagged in the system log.

    SyslogIdentifier=myapp



    # Auto-Restart the container after a crash.

    Restart=always



    [Install]

    # make sure service is started after docker is up

    WantedBy=docker.service