Regular readers of this blog know that I’m using Jekyll to generate the static site.
I’m using GitLab:
when I push on the master branch, it triggers the generation job.
However, Jekyll is Ruby-based and requires a couple of Gem dependencies.
I’ve also added a few plugins.
For this reason, I’ve created a Docker image with all required dependencies.
Regularly, I update the versions in the Gemfile.lock via Bundler.
Afterward, I need to rebuild the Docker image.
Hence, two jobs are necessary:
- After a push containing a change that influences the Docker image, build it
- After any push, generate the site.
For the first, the trigger condition is whether any of the following files have been changed:
Gemfile.lock, Dockerfile and .gitlab-ci.yml.
The problem is how to run a build only if the condition is met, as it’s an expensive and time-consuming operation.
GitLab’s build file configuration offers a solution for this.
In a job, you can configure an only clause to run only if a condition is met.
The condition can be:
- A reference, e.g., a branch, or a tag
- A trigger, e.g., a push, the web UI or an API call
- The value of a variable
- A change on a specific file
- A couple of others
The next to last option is the answer to our problem. We can configure a set of files, and if any of them has been changed, the build should run. Otherwise, do nothing.
It translates into the following structure:
stages:
- image (1)
- deploy (1)
build: (2)
stage: image (2)
image:
name: gcr.io/kaniko-project/executor:debug
entrypoint: [""]
script: # Build the Docker image
only:
refs:
- master (4)
changes:
- Gemfile.lock (5)
- Dockerfile (5)
- .gitlab-ci.yml (5)
pages: (3)
stage: deploy (3)
image:
name: registry.gitlab.com/nfrankel/nfrankel.gitlab.io:latest
script: # Generate the site
only:
refs:
- master| 1 | Define the two stages |
| 2 | Define the build job in the image stage.
The job creates the Docker image (via Kaniko) |
| 3 | Define the pages job in the deploy stage.
The job generates the site via Jekyll |
| 4 | Build the master branch only |
| 5 | Only build the image if any of these files have changed |
At this point, each change triggers the build: the image building job runs before the site generation, but GitLab skips the former if the image hasn’t changed.