iirc, if you are invoking the same build project from the pipeline they would indeed be queued, even more so if you have the same artifact input for the action in your stage. But what you might be looking at doing is to shift from having CodePipeline do the parallel work and use AWS CodeBuild in batch mode for that. Have been using it since it came out and saved us a lot of time.
In essence, CodeBuild creates forked executions based on the batch definition you are using. From there, you execute multiple jobs in parallel. The output of each one can be independent as much as be grouped/merged together in a final build process.
Here are some public examples I have: https://github.com/compose-x/docker-python https://github.com/compose-x/corretto-docker/blob/codebuild/.codebuild/buildspec_batch.yaml
In both above cases, I use codebuild batch to build images in ARM and x86, and at the end group them all together to publish docker manifest.
Hope this helps.
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