Use GitLab CI/CD and Test Boosters to run tests in parallel
Test Boosters (https://github.com/renderedtext/test-boosters/) take your test suite and split the test files into multiple jobs. This allows you to quickly parallelize your test suite across multiple build machines.
The opensource version doesn't automatically balance the load based on execution time, but it is still valuable. You can also define you preferred split configuration if you already want to force specific tests in specific jobs.
The usage is quite simple:
rspec_booster --job 1/10
This command splits your test files in 10 slots, and then execute the first one.
We should create a blog post (or probably a technical article) to document how to use them out of the box.