GitHub Actions path filtering for monorepo CI

<p>Monorepo contains multiple services (api/, frontend/, mcp-server/). Every push runs all CI pipelines even when only one service changed. Need to run only the relevant pipelines based on which files changed.</p>

<p>Use <code>paths</code> filter and the <code>dorny/paths-filter</code> action for selective CI:</p> <div class="highlight"><pre><span></span><code><span class="c1"># .github/workflows/api-ci.yml</span> <span class="nt">name</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">API CI</span> <span class="nt">on</span><span class="p">:</span> <span class="w"> </span><span class="nt">push</span><span class="p">:</span> <span class="w"> </span><span class="nt">branches</span><span class="p">:</span><span class="w"> </span><span class="p p-Indicator">[</span><span class="nv">main</span><span class="p p-Indicator">,</span><span class="w"> </span><span class="s">'feat/**'</span><span class="p p-Indicator">]</span> <span class="w"> </span><span class="nt">paths</span><span class="p">:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="s">'api/**'</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="s">'.github/workflows/api-ci.yml'</span> <span class="w"> </span><span class="nt">pull_request</span><span class="p">:</span> <span class="w"> </span><span class="nt">paths</span><span class="p">:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="s">'api/**'</span> <span class="nt">jobs</span><span class="p">:</span> <span class="w"> </span><span class="nt">test</span><span class="p">:</span> <span class="w"> </span><span class="nt">runs-on</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">ubuntu-latest</span> <span class="w"> </span><span class="nt">defaults</span><span class="p">:</span> <span class="w"> </span><span class="nt">run</span><span class="p">:</span> <span class="w"> </span><span class="nt">working-directory</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">api</span> <span class="w"> </span><span class="nt">steps</span><span class="p">:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">uses</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">actions/checkout@v4</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">name</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">Install uv</span> <span class="w"> </span><span class="nt">uses</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">astral-sh/setup-uv@v3</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">run</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">uv sync --frozen</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">run</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">uv run pytest</span> <span class="c1"># For complex path-based conditions in a single workflow:</span> <span class="c1"># .github/workflows/ci.yml</span> <span class="nt">name</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">Monorepo CI</span> <span class="nt">on</span><span class="p">:</span> <span class="w"> </span><span class="nt">push</span><span class="p">:</span> <span class="w"> </span><span class="nt">branches</span><span class="p">:</span><span class="w"> </span><span class="p p-Indicator">[</span><span class="nv">main</span><span class="p p-Indicator">]</span> <span class="nt">jobs</span><span class="p">:</span> <span class="w"> </span><span class="nt">detect-changes</span><span class="p">:</span> <span class="w"> </span><span class="nt">runs-on</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">ubuntu-latest</span> <span class="w"> </span><span class="nt">outputs</span><span class="p">:</span> <span class="w"> </span><span class="nt">api</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">${{ steps.filter.outputs.api }}</span> <span class="w"> </span><span class="nt">frontend</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">${{ steps.filter.outputs.frontend }}</span> <span class="w"> </span><span class="nt">steps</span><span class="p">:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">uses</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">actions/checkout@v4</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">uses</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">dorny/paths-filter@v3</span> <span class="w"> </span><span class="nt">id</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">filter</span> <span class="w"> </span><span class="nt">with</span><span class="p">:</span> <span class="w"> </span><span class="nt">filters</span><span class="p">:</span><span class="w"> </span><span class="p p-Indicator">|</span> <span class="w"> </span><span class="no">api:</span> <span class="w"> </span><span class="no">- 'api/**'</span> <span class="w"> </span><span class="no">- 'docker-compose.yml'</span> <span class="w"> </span><span class="no">frontend:</span> <span class="w"> </span><span class="no">- 'frontend/**'</span> <span class="w"> </span><span class="nt">api-tests</span><span class="p">:</span> <span class="w"> </span><span class="nt">needs</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">detect-changes</span> <span class="w"> </span><span class="nt">if</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">needs.detect-changes.outputs.api == 'true'</span> <span class="w"> </span><span class="nt">runs-on</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">ubuntu-latest</span> <span class="w"> </span><span class="nt">steps</span><span class="p">:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">uses</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">actions/checkout@v4</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">name</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">Run API tests</span> <span class="w"> </span><span class="nt">working-directory</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">api</span> <span class="w"> </span><span class="nt">run</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">make test</span> <span class="w"> </span><span class="nt">frontend-tests</span><span class="p">:</span> <span class="w"> </span><span class="nt">needs</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">detect-changes</span> <span class="w"> </span><span class="nt">if</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">needs.detect-changes.outputs.frontend == 'true'</span> <span class="w"> </span><span class="nt">runs-on</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">ubuntu-latest</span> <span class="w"> </span><span class="nt">steps</span><span class="p">:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">uses</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">actions/checkout@v4</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">name</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">Run frontend tests</span> <span class="w"> </span><span class="nt">working-directory</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">frontend</span> <span class="w"> </span><span class="nt">run</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">npm test</span> <span class="w"> </span><span class="c1"># Always runs to provide a consistent required status check</span> <span class="w"> </span><span class="nt">ci-success</span><span class="p">:</span> <span class="w"> </span><span class="nt">needs</span><span class="p">:</span><span class="w"> </span><span class="p p-Indicator">[</span><span class="nv">api-tests</span><span class="p p-Indicator">,</span><span class="w"> </span><span class="nv">frontend-tests</span><span class="p p-Indicator">]</span> <span class="w"> </span><span class="nt">if</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">always()</span> <span class="w"> </span><span class="nt">runs-on</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">ubuntu-latest</span> <span class="w"> </span><span class="nt">steps</span><span class="p">:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="nt">run</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">echo "CI complete"</span> </code></pre></div> <p>The <code>paths</code> filter at the <code>on:</code> level skips the workflow entirely. <code>dorny/paths-filter</code> gives per-job control within a workflow. Always include a final <code>ci-success</code> job with <code>if: always()</code> to satisfy required status checks when earlier jobs are skipped.</p>