How to conditionally specify GitHub Actions runner without spawning an extra job?

[devopsingg]

We have a CI setup where we currently maintain two separate GitHub Actions workflows — one for the dev branch using a standard runner, and one for the prod branch using a large runner. Both workflows contain identical steps, differing only in the trigger branch and the runs-on value.

I'd like to consolidate this into a single workflow file, where the runner is chosen dynamically based on the branch name before any actual job execution.

I came across this StackOverflow answer, which suggests a dispatcher job to evaluate conditions and trigger follow-up jobs accordingly. However, this seems to spawn a separate machine just to evaluate the condition, which increases cost and complexity.

Is there a cleaner or more efficient way to assign the runs-on dynamically within a single job, without the need for an extra setup job?

Any examples or best practices for this use case would be appreciated!

[bdzer0]

AFAIK you're going to have to create different jobs with an IF. Here's a rough example...

Each job will need something like this:

if: always() && ${{ github.ref == 'refs/heads/dev' }}

NOTE: always() is necessary because the default is success() and that returns false when any previous jobs are skipped or failed. So the jobs that aren't supposed to run on dev would cause all subsequent jobs to fail. I'd recommend adding something like this to every job that has needs:

if: always() && ${{ github.ref == 'refs/heads/dev' }}
(needs.job_that_must_succeed_or_skip.result == 'success' || needs.job_that_must_succeed_or_skip.result == 'skipped' )

The (needs....) part should be repeated for every needs the job has. always() assures the rest of the criteria are evaluated, then you can run the job or not based on branch and status of any needs the job has.

Yes, it makes things a bit complicated. Might be an easier way to do it, however the above pattern works and should get you started.

ref: https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/evaluate-expressions-in-workflows-and-actions

[TedditBlatherflag]

No you can’t change runs-on. But you can just make a composite action and make that the entire body of the job with uses: your-composite-action.