A guide to get you started with the implementation of a software build pipeline in Travis CI that automatically gets your code released to GitHub and pushed to a Docker registry. It takes you through some extra features such as Java’s JAR signing (GPG) and encryption of secret data for your build. The examples assume that Java and Maven are in use. Furthermore, if releasing to Maven Central is your goal, this guide will take you right there at the door.
For every commit pushed to the master branch in GitHub, the following tasks should be completed by Travis:
- Software is built and dependencies are resolved.
- Artifacts are signed.
- Docker image is built.
- Tests run.
- Image is pushed with tag ‘latest’ to Docker Hub.
These are the basics that should invariably happen. Additionally, as a consequence of the command:
Travis should also trigger:
- Maven to set a new version based on the Git tag name.
- Docker to push an image with the same tag as the Git tag name.
- Creation of a new GitHub release with all artifacts, javadocs, sources and signature files.
Make sure Travis and GitHub integration are properly set up.
One of the great advantages of CI tools like Travis is that the build configuration is defined as code and version controlled with the rest of your project in Git. In practice, this means you should have a .travis.yml file checked in your repository.
JAR Sign and Encryption
In the before_install step of the .travis.yml example above, there is a command to decrypt a codesign.asc.enc file to a decrypted codesign.asc one. This is done securely because my repository, in Travis, is the only one with a private key to decrypt it. Previously, I had used Travis CLI in my local machine to encrypt that file with the public key available in the corresponding Travis build repo.
The codesign.asc is nothing more than another private key I have once created with GPG. Since it is a requirement from Maven Central to have signed JARs, I found useful to include it as part of my builds. There are plenty of resources out there explaining how to work with the GnuPG tool.
A Maven plugin has the job to do the actual JAR signing. For this case, it assumes my key is set as default in the environment (gpg –fast-import). The passphrase is expected to be configured ahead in Travis as an environment variable: $GPG_PASSPHRASE.
The pom.xml for this example can be found here.
Pay attention to the variables $DOCKER_USERNAME and $DOCKER_PASSWORD. They should be manually assigned in Travis (same as $GPG_PASSPHRASE) and in my case they refer to my own Docker Hub credentials.
Besides the build and push steps, one good idea might be executing a ‘docker run’ during the ‘script’ stage and conditionally fail or pass the build.
Every successful build derived from master and with a tag is directly posted to a GitHub release. An access token (api_key) is required by Travis, but again the command line tool handles that for you.
Much has been said about continuous delivery. I strongly agree it is a matter of process and people before anything else. Nonetheless, I don’t find examples or how-to’s out there quite often. Probably because the resulting implementation is specific to the development process in place. I hope you can use this to get you started and evolve it towards your own deployment pipeline.
The solution presented in this blog came from my Java Starter project. Check out the source code at https://github.com/juliaaano/java-starter.