Ansible role to run dockers

An ansible role to install the docker daemon and build and run dockers.

It installs the docker daemon and ensure it is up and running. It sets the STORAGE_DRIVER if the docker host uses systemd and it configures the MTU to 1450 if it is a VM running on OpenStack. It builds and runs docker images on the docker host.

Requirements

This Ansible role requires at least Ansible version 1.9.

Role Variables

• docker_check_kernel - The minimum kernel version allowed on hosts to run docker.

# minimum kernel version
docker_check_kernel: '3.10'

• docker_check_machine - The hosts architecture needed to run docker.

# architecture
docker_check_machine: 'x86_64'

• docker_package - The name of the docker package.

# The docker package name
docker_package: docker

• docker_packages - A list of packages to install/remove before installing the docker package.

# A list of package to install/remove
# docker_packages:
#   - { "name": "docker", "state": "absent" }

• docker_init_config_directory - The location of the configuration file of the docker daemon init script.

# Location of configuration files loaded by the init script
docker_init_config_directory: "/etc/sysconfig"

• docker_opts - The name of the environment variable used to pass options to the docker daemon.

# docker daemon options environment variable
docker_opts: "OPTIONS"

• docker_services - A list of system services to start

# services
docker_services:
  - docker

• dockers - A list of docker images to build and run on the docker host with the docker-build and docker-run commands

# dockers
# dockers:
#   - nginx

• docker_cluster - An optional cluster name to pass to the docker-build and docker-run commands

# docker cluster
# docker_cluster: ""

• docker_cluster - Starts the dockers if set to true.

# Start docker
docker_start: true

• docker_restart - Restarts dockers when their image has been updated. It removes current running dockers and start new ones.

# Stop and remove running docker to start a new one when image has been updated
docker_restart: true

• docker_force_restart - Restart dockers, even if image has not been updated. It removes current running dockers and start new ones.

# Stop and remove running docker to start a new one even if image has not been updated
docker_force_restart: false

Helper scripts

This role comes with a few helper scripts. Here is a short description.

• docker-build - Build a docker image, reading options to pass to the docker build command from a Dockeropts file.

• docker-cleanup - Remove unused dockers.

• docker-cleanup-images - Remove unused docker images.

• docker-cleanup-volumes - Remove unused docker volumes.

• docker-get-image - Return sha256 of the image used by the docker.

• docker-get-status - Return the status of the docker.

• docker-log-cleanup - Empty the file logging the docker output on the docker host.

• docker-log-truncate - Truncate the file logging the docker output on the docker host.

• docker-run - Run a docker, reading options to pass to the docker run command from a Dockeropts file.

Example

To launch this role on your docker hosts, run the default playbook.yml.

$ ansible-playbook playbook.yml

Build a docker image

On the docker hosts, you'll be able to build docker images and run dockers, based on Dockerfile and Dockeropts files located in the /etc/docker subdirectories.

To create an nginx docker image, create a directory /etc/docker/nginx with a Dockerfile and a Dockeropts files into.

# mkdir -p /etc/docker/nginx
# cat << EOF > /etc/docker/nginx/Dockerfile
FROM nginx:alpine
EOF
# cat << EOF > /etc/docker/nginx/Dockeropts
DOCKER_ULIMIT="nofile=65536"
DOCKER_PORT="80:80"
EOF

Build your nginx docker image, then run it ! The docker-run command will read the Dockeropts file to add the --ulimit and --port options to the docker run command.

# docker-build nginx && docker-run nginx

Override your files

If you want to copy a file in your Dockerfile, say the default nginx.conf, you can use the DOCKER_BUILD_PREFIX and DOCKER_BUILD_SUFFIX variables to get different versions of this file giving some context.

# cat << EOF > /etc/docker/nginx/Dockerfile
FROM nginx:alpine
ARG DOCKER_BUILD_PREFIX
ARG DOCKER_BUILD_SUFFIX
COPY ./\${DOCKER_BUILD_PREFIX}nginx.conf\${DOCKER_BUILD_SUFFIX} /etc/nginx/nginx.conf
EOF

You can now override the nginx configuration file when you build your image.

• Without option, the docker-build command will search for the file beside your Dockerfile.

# docker-build nginx && docker-run nginx

Both DOCKER_BUILD_PREFIX and DOCKER_BUILD_SUFFIX variables are empty, the Dockerfile will search for a ./nginx.conf file, ie the /etc/docker/nginx/nginx.conf file.

• With a -c|--cluster option, the docker-build command will search for the file in a subdirectory below your Dockerfile.

# docker-build -c custom nginx && docker-run -c custom nginx

The DOCKER_BUILD_PREFIX variable is populated with 'custom/' to force the Dockerfile to search for a ./custom/nginx.conf file, ie /etc/docker/nginx/custom/nginx.conf file.

• Whith an image name suffixed with a dash, the docker-build command will search for a suffixed file as well.

# docker-build -c custom nginx-develop && docker-run -c custom nginx-develop

The DOCKER_BUILD_PREFIX variable is populated with 'custom/' and the DOCKER_BUILD_SUFFIX variable is populated with '-develop' to force the Dockerfile to search for a ./custom/nginx.conf-develop file, ie /etc/docker/nginx/custom/nginx.conf-develop file.

Override your options

The same override principle can be used for the Dockerfile and the Dockeropts file when using the docker-build and docker-run commands. You can create a /etc/docker/nginx/custom/Dockeropts file that would override your default Dockeropt file, and a /etc/docker/nginx/custom/Dockeropts-develop file overriding both other files too. The Dockeropts file accepts the following options.

• SYSCTL - values to set on the docker host via the sysctl command before running the docker
• DOCKER_ARGS - values to pass to the docker build command with --build-arg options
• DOCKER_ENV - values to pass to the docker run command with -e options
• DOCKER_LINK - values to pass to the docker run command with --link options
• DOCKER_OPT - values to pass to the docker run command with prefixed by --
• DOCKER_PORT - values to pass to the docker run command with -p options
• DOCKER_ULIMIT - values to pass to the docker run command with --ulimit options
• DOCKER_VOLUME - values to pass to the docker run command with -v options
• HOST_VOLUME - volumes to allow write access to from the docker on selinux enabled host

Overriding options is done several times, reading options from the more specific to the more generic file. In our example, files are read in this order : /etc/docker/nginx/custom/Dockeropts-develop /etc/docker/nginx/custom/Dockeropts /etc/docker/nginx/Dockeropts

Common configuration

Following configuration builds and runs the docker image 'nginx-develop' for the 'custom' cluster described in our example. The Dockerfile and Dockeropts files needed in the /etc/docker/nginx directory should be present on the docker host, likely synchronised by an other ansible role.

docker_cluster: "custom"
docker:
  - nginx-develop

Tests

To test this role on your docker hosts, run the tests/playbook.yml playbook.

$ ansible-playbook tests/playbook.yml

Limitations

This role is known to work on Ubuntu, Debian, CentOS and Alpine Linux.