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Pull Request based workflow

Note: In this exercise we use the term "main" to refer to the main stabilization branch, or the default branch. This can also have the name "trunk" or "master", but all is refering back to the same thing.

The defacto-standard workflow now-adays is the Pull Request workflow (also known as the GitHub flow)

It utilizes the pull request feature to merge code from developer branches to main.

Securing your main branch

Securing your branch

We do not want everybody to be able to push directly to main, without the CI server checking the quality of the code. So we need our Git repository to block incoming pushes directly to main. In that way we can ensure that the only way in to main is through a PR. This can be done in GitHub under settings->Branches, Branch protection rules and then click on add rule.

Tasks

  • Go to your repository on GitHub enter settings.

  • Go to Branches and add a branch protection rule.

  • Give it the pattern main.

  • Require status checks to pass before merging Will block the pull request from merging until the tests have passed.

  • Require branches to be up to date before merging The branch must be up to date with the base branch before merging.

  • Add the following jobs to the Status checks that are required selection: Test,Build,Docker-image. In that way, no one can push to main without having the tests pass.

  • Do not allow bypassing the above settings Makes the rules apply to everyone (yes, you too!).

  • OPTIONAL: Require linear history requires the PR branch to be rebased with the target branch, so a linear history can be obtained. Further explanaition here. This is a very strict way of using git, and is only here for inspiration for experiments.

  • Try to push to main to verify that you cannot.

Triggering the build on a PR

So how do we then get the CI server to run the tests on a PR? Right now our pipeline gets triggered by any push to any branch.

We want our pipeline to trigger on both pushes and pull requests towards main only.

The way thar pipelines gets triggered is by using the on field in the workflow.

Tasks

Hint if you get stuck 
on:
  # Trigger the workflow on push or pull request,
  # but only for the main branch
  push:
    branches:
      - main
  pull_request:
    branches:
      - main
  • Try to make a couple of different branches that you push up to github and make pull requests on. It could be that you in one broke the unit tests to see that the CI system caught that, and another where you make your branch diverge from what is on main now, triggering the build-in github rules.

Note: When you make a pull request on your forked repository, GitHub will make target branch the main of the original repo. You need to change it manually to make the pull request based on your fork.

Change pull request base branch

Looking at your pull requests, you should see that the pipeline is triggered for each of them, and that only if the tests are passing that you can merge the PR.

PR with passing tests]

What about the rest?

You want to run tests on your development branches as well, even if you are not pushing to main right away.

For that we need to add another workflow to the repository.

We want to run a slightly shorter workflow, excluding the component test, and the push of docker images. We want to run in on all branches that has the prefix dev/.

tasks

  • Copy the workflows/pr-workflow.yml file to a new file called workflows/dev-workflow.yml.
  • Change the on field to:
on:
  push:
    branches:
      - "dev/**"
  • delete the Component-test: job from the jobs section.
  • delete the name: push docker step from the Docker-image job.

Trying it out

Congratulations! If everything works as intended, you now have a full "grown up" pipeline, with conditions, and security that your main branch always contains tested code. Go ahead and try it out, to see what it feels like.

Further reading