Docker Cookbook

2.12 Setting Up an Automated Build on Docker Hub for Continuous Integration/Deployment | 63

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Figure 2-4. Entering details of the build
The name of the Docker Hub repository you are creating does not
have to be the same as the GitHub/Bitbucket repository you select.
Once you have set up the build, you have access to the build details. The status
changes from 
pending
to 
building
to 
pushing
and finally to 
finished
. When the build is
finished, you can pull the new image:
$ docker pull runseb/flask
The Dockerfile tab automatically populates with the content of your Dockerfile in
your GitHub repository. The Information tab automatically populates with the con‐
tent of the 
README.md
file if it exists.
64 | Chapter 2: Image Creation and Sharing

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As soon as you push a new commit to the GitHub repo used for the build, a new
build is triggered. When the build finishes, the new image will be available.
You can edit the build settings to trigger builds from different
branches and specify a different tag. For instance, you can decide to
build from your master branch and associate the 
latest
tag to it,
and use a release branch to build a different tag (i.e., 
1.0
tag from a
1.0
release branch).
Discussion
In addition to builds being automatically triggered when you push to your GitHub or
Bitbucket repository, you can trigger builds by sending an HTTP POST request to a
specific URL generated on the Build Trigger page (see 
Figure 2-5
). To prevent abusing
the system, builds may be ignored.
Figure 2-5. Turning on the build trigger
Finally, whether you build automatically or use a trigger on your own, you can also
use webhooks. Webhook URLs are useful for integrating with other tools, like 
Jen‐
kins
. Various tools can trigger image builds and chain several steps of a continuous