If you use docker.io (or any similar service) to build your Docker containers, it may be possible that, once the new image is generated, you want your Docker host to automatically pull it and restart the container.

Docker.io gives you the possibility to set a web hook after a successful build. Basically it does a POST on a defined URL and send some informations in JSON format.

docker-puller listens to these web hooks and can be configured to run a particular script, given a specific hook. It’s a very simple service I wrote using Python/Flask. It’s also my first Flask application, so if you want to improve it, feel free to send me a pull request on GitHub.

Note: this is not the only existing service that is able to do this task. I took inspiration from this article http://nathanleclaire.com/blog/2014/08/17/automagical-deploys-from-docker-hub/ and I really tried to customize https://github.com/cpuguy83/dockerhub-webhook-listener for my own needs, but the problem is that dockerhub-webhook-listener is not ready to be used as is (you have to customize it) and I’m not very good with Golang (yet) to be able to do it in little time. This is why I rewrote the service in Python (that is my daily language). I want to thank Brian Goff for the idea and all the people in #docker @ FreeNode for the support.

How to use docker-puller

Setting up the service should be quite easy. After you clone the repository from https://github.com/glowdigitalmedia/docker-puller there is a config.json file where you define the host, port, a token and a list of hooks you want to react to. For example:

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{
    "host": "localhost",
    "port": 8000,
    "token": "abc123",
    "hooks": {
        "hello": "scripts/hello.sh"
    }
}

Create a bash script (in this case it was called hello.sh) and put it under script folder and write the instructions to be executed to pull the new image and restart the container (example):

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docker pull andreagrandi/test:latest
docker stop test
docker rm test
docker run --name test -d -p 8000:80 andreagrandi/test:latest

Once configured, I suggest you to setup a Nginx entry (instructions not covered here) that for example redirect yourhost.com/dockerpuller to localhost:8000 (I would advise to enable SSL too, or people could be able to sniff your token). The service can be started with: “python app.py” (or you can setup a Supervisor script).

At this point docker-puller is up and running. Go to docker.io automatic build settings and setup a webhook like this: http://yourhost.com/dockerpuller?token=abc123&hook=hello

Every time docker.io finishes building and pushing your image to the docker registry, it will POST on that URL. docker-puller will catch the POST, check for a valid token, get the hook name and will execute the relative script.

That’s all! I hope this very simple service can be useful to other people and once again, if you want to improve it, I will be glad to accept your pull requests on GitHub.