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Dockerize

Dockerize is a command-line bash utility for managing Docker containers. This is the sort of Docker workflow that it's meant to automate:

• let's take a Ruby example app, hi_sinatra. It has its own Github repository and we have a simple, non-git Jenkins job for it.

• every commit pushed to Github, regardless of the branch, triggers a Jenkins build (via Amazon SQS). All Jenkins builds will result in a Docker image. A successful build will produce a running Docker container. A failed build will produce a stopped container which can be investigated by either looking at the logs or starting it with a tty attached.

• if Docker doesn't have a hi_sinatra:master pre-built image, a new one will be created from the master branch. This master image gets re-built every time there's a commit against the master branch. Having a master image speeds up image builds considerably (eg. installing Ruby gems, installing node modules, C extensions etc). The resulting image won't use any caching and all intermediary images will be removed. Just to clarify, this image will not be shipped into production.

• if a Docker image with that app's name, branch name and git commit sha doesn't exist, we want Docker to build it for us. At this point, we're interested to have the eg. hi_sinatra:second-blog-post.a8e8e83 Docker image available.

• before a new container can be started from the image that we've just built, all services that the app requires must be running in their own independent containers. Our hi_sinatra example app requires a running Redis server.

• when all dependent services are running in their own containers, we start a container from the newly built app image (in our example, hi_sinatra:second-blog-post.a8e8e83). All dependent containers will have their IPs exposed via env options, eg. docker run -e REDIS_HOST=172.17.0.8 -d ...

• before our hi_sinatra app starts in its new Docker container, all tests must pass - both unit, integration and acceptance. Full stack tests (also known as acceptance tests) use sandbox services, but they are setup via the same Docker containers that will be made available in production. Code portability is Docker's strongest point, we're making full use of it.

• if everything worked as expected, including interactions with all external services, this Docker image will be tagged as production. The service responsible for bringing up new Docker containers from the latest production images will take it from here.

Related blog post: Continuous Delivery with Docker and Jenkins - part II