Installs Docker on Ubuntu.

Well tested on 14.04. Has been known to work on 12.04.

This role started from the angstwad docker_ubuntu role and has since forked a bit, primarily to manage which version of Docker we install. Because of interdepencies between the Docker API version and software that we install (especially docker-py), we have to be careful about Docker versions.

• Our initial deploys used a fixed version of LXC Docker, pinned at 1.5.0
• Our newer deploy will still use a pinned version Docker Engine, but will be able to specify their own versions (e.g. 1.8.1)

This role no longer directly supports upgrading docker from a previous version. Any additional steps required as a part of an upgrade should be taken care of in a separate role or playbook.

Docker has some kernel requirements for proper usage with Ubuntu. We have a new role ansible-role_kernel_update which will assist with the kernel requirements.

• docker_version: this variable controls the version of Docker that is installed. Required. If version 1.5.0 is selected, LXC Docker will be used; otherwise the stated version of Docker Engine will be installed (if available).
• docker_daemon_flags: Empty by default. This variable holds flags that will be passed to the Docker daemon on startup. (This is implemented by modifying the file /etc/default/docker.)
• docker_daemon_startup_retries: this variable controls how many times we poll docker to confirm it is running after we start or restart it before giving up. Defaults to 10.

The documentation for working with Docker on Ubuntu is available online but there has been some refactoring of the documentation since the original writing.

• https://docs.docker.com/engine/installation/linux/ubuntu/
• (old) https://github.com/docker/docker.github.io/blob/master/engine/installation/linux/ubuntulinux.md
• (new) https://github.com/docker/docker.github.io/blob/master/engine/installation/linux/ubuntu.md

The old documentation is what was previously available online and the new documentation is what is currently available online. As of this writing the documentation is at commit '45a19ec' & '9093e0a' respectively.

• (old) https://github.com/docker/docker.github.io/blob/45a19ec/engine/installation/linux/ubuntulinux.md
• (new) https://github.com/docker/docker.github.io/blob/9093e0a/engine/installation/linux/ubuntu.md

Links to documentation will therefore get pinned to a particular commit to maintain access to historical information which may get removed (or moved) in later versions. Maintainers should check the master branch when updating the role and update links when possible.

Currently the new documentations says docker is only supported on 14.04[LTS], 16.04[LTS], & 16.10 but the old documentation has some instructions for 12.04[LTS].

12.04 may not have support due to issues with older kernels. Docker documentation mentions some prerequisites when installing from a binary that could be informative and there is a known issue with docker running on linux kernels less than 3.19 that could imply 12.04 isn't supported.

• https://docs.docker.com/engine/installation/binaries/#/prerequisites
• moby/moby#21704 (comment)

Users of this role might also consider reviewing our other ansible roles. In particular:

• https://github.com/locationlabs/ansible-role_docker-base

There's a directory "tests" with some Ansible playbooks that can be used for verifying role behavior. See tests/TESTS.md for more information.

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