The CI pipeline takes 40 minutes. Developers are merging without waiting. How do you cut it to 10?

Question

A monorepo with 6 services. Every PR runs every test suite and builds every image.

Accepted Answer

- Measure first: which stages take the time? Usually dependency installs, image builds and one slow test suite.
- Only run what changed: path filters or a build graph (Nx, Bazel, Turborepo) so a change to one service doesn't test all six.
- Cache: dependency caches keyed on the lockfile, Docker layer cache (BuildKit with a registry or GHA cache).
- Parallelise: split test suites across runners, run lint, unit tests and builds in parallel.
- Move slow end-to-end suites to a merge queue or post-merge stage, with a fast smoke set on PRs.
- Fix flaky tests or quarantine them, because retries hide real time.

The CI pipeline takes 40 minutes. Developers are merging without waiting. How do you cut it to 10?

The scenario

Model answer

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