Merge 3b3fb41561 into 638ed79f9d

Add note on runner versions

README.md

@@ -19,16 +19,19 @@ See ["Caching dependencies to speed up workflows"](https://docs.github.com/en/ac
 
 The cache backend service has been rewritten from the ground up for improved performance and reliability. [actions/cache](https://github.com/actions/cache) now integrates with the new cache service (v2) APIs.
 
-The new service will gradually roll out as of **February 1st, 2025**. The legacy service will also be sunset on the same date. Changes in these release are **fully backward compatible**.
+The new service will gradually roll out as of **February 1st, 2025**. The legacy service will also be sunset on the same date. Changes in these releases are **fully backward compatible**.
 
 **We are deprecating some versions of this action**. We recommend upgrading to version `v4` or `v3` as soon as possible before **February 1st, 2025.** (Upgrade instructions below).
 
-If you are using pinned SHAs, please use the SHAs of versions `v4.2.0` or `v3.4.0`
+If you are using pinned SHAs, please use the SHAs of versions `v4.2.0` or `v3.4.0`.
 
 If you do not upgrade, all workflow runs using any of the deprecated [actions/cache](https://github.com/actions/cache) will fail.
 
 Upgrading to the recommended versions will not break your workflows.
 
+> **Additionally, if you are managing your own GitHub runners, you must update your runner version to `2.231.0` or newer to ensure compatibility with the new cache service.**  
+> Failure to update both the action version and your runner version may result in workflow failures after the migration date.
+
 Read more about the change & access the migration guide: [reference to the announcement](https://github.com/actions/cache/discussions/1510).
 
 ### v4

caching-strategies.md

@@ -287,3 +287,26 @@ steps:
   - name: Publish package to public
     run: ./publish.sh
 ```
+
+### Saving cache only if the build runs on the default branch
+
+Workflow runs can restore caches created in either the current branch or the default branch (usually `main`) [Reference](https://docs.github.com/en/actions/reference/workflows-and-actions/dependency-caching#restrictions-for-accessing-a-cache).
+
+By restricting caches to the default branch, we can reduce the risk that Github evicts a cache created on the default branch. If that happens, every PR will create its own cache, increasing the cache churn.
+
+We can condition the execution of the `actions/cache/save` action on the current branch:
+
+```yaml
+steps:
+  - uses: actions/checkout@v3
+  .
+  . // restore if need be
+  .
+  - name: Build
+    run: /build.sh
+  - uses: actions/cache/save@v3
+    if: ${{ github.ref == 'refs/heads/main' }} // check we are on the default branch
+    with:
+      path: path/to/dependencies
+      key: ${{ runner.os }}-${{ hashFiles('**/lockfiles') }}
+```