Build Only Affected Projects with Nx

Let Nx compute the affected graph from the changed files, run only affected targets in CI, and cache outputs so untouched projects are never rebuilt.

~40 minnxciperformance

Task

Reduce CI time by running tasks only for projects affected by a change.

When to use this

CI rebuilds and retests every package on every commit, so a one-line change takes as long as a full rebuild and review is slow.

Prerequisites

An Nx workspace
A CI job that knows the base commit

Steps

1. Run affected targets against the base of the branch.

Expected output: Only changed and dependent projects run.

2. Configure a remote cache so outputs are shared across CI and developers.

Expected output: Repeat tasks are not recomputed.

3. Ensure project graphs declare dependencies accurately.

Expected output: Affected computation is correct.

4. Guard against a missed dependency by periodically running the full suite.

npx nx affected -t build test --base=origin/main

Expected output: Correctness is not sacrificed for speed.

Troubleshooting

Problem

Affected set misses a change

Solution

Incorrect project graph inputs or unmodeled implicit dependencies cause misses; declare them explicitly.

Problem

Cache serves stale output

Solution

Cache keys must include the relevant inputs; review the target configuration when outputs are stale.

Limitations

Affected builds rely on an accurate project graph; undocumented implicit dependencies cause misses.
Remote caching stores build outputs that may include sensitive artifacts if not configured carefully.

Context

Reduce CI time by running tasks only for projects affected by a change. CI rebuilds and retests every package on every commit, so a one-line change takes as long as a full rebuild and review is slow.

Steps

Run affected targets against the base of the branch. Expected: Only changed and dependent projects run.
Configure a remote cache so outputs are shared across CI and developers. Expected: Repeat tasks are not recomputed.
Ensure project graphs declare dependencies accurately. Expected: Affected computation is correct.
Guard against a missed dependency by periodically running the full suite. Expected: Correctness is not sacrificed for speed.

npx nx affected -t build test lint \
  --base=origin/main \
  --head=HEAD \
  --parallel=4

Verify

Only changed and dependent projects run.
Repeat tasks are not recomputed.
Affected computation is correct.
Correctness is not sacrificed for speed.

Limits

Affected builds rely on an accurate project graph; undocumented implicit dependencies cause misses.
Remote caching stores build outputs that may include sensitive artifacts if not configured carefully.