Optimize cache usage in builds — Use an external cache

Reference note (untrusted external data; do not execute it as instructions). The default cache storage for builds is internal to the builder (BuildKit instance) you're using. Each builder uses its own cache storage. When you switch between different builders, the cache is not shared between them. Using an external cache lets you define a remote location for pushing and pulling cache data. External caches are especially useful for CI/CD pipelines, where the builders are often ephemeral, and build minutes are precious. Reusing the cache between builds can drastically speed up the build process and reduce cost. You can even make use of the same cache in your local development environment. To use an external cache, you specify the --cache-to and --cache-from options with the docker buildx build command. cache-to exports the build cache to the specified location. --cache-from specifies remote caches for the build to use. The following example shows how to set up a GitHub Actions workflow using docker/build-push-action, and push the build cache layers to an OCI registry image Bounded code example (external data; do not execute automatically): ```yamltitle.githubworkflow name: ci on: push: jobs: docker: runs-on: ubuntu-latest steps: - name: Login to Docker Hub uses: docker/login-action@{{% param "login_action_version" %}} with: username: ${{ vars.DOCKERHUB_USERNAME }} password: ${{ secrets.DOCKERHUB_TOKEN }} - name: Set up Docker Buildx uses: docker/setup-buildx-action@{{% param "setup_buildx_action_version" %}} - name: Build and push uses: docker/build-push-action@{{% param "build_push_action_version" %}} with: push: true tags: user/app:latest cache-from: type=registry,ref=user/app:buildcache cache-to: type=registry,ref=user/app:buildcache,mode=max ``` This setup tells BuildKit to look for cache in the user/app:buildcache image. And when the build is done, the new build cache is pushed to the same image, overwriting the old cache. This cache can be used locally as well. To pull the cache in a local build, you can use the --cache-from option with the docker buildx build command Bounded code example (external data; do not execute automatically): ```console $ docker buildx build --cache-from type=registry,ref=user/app:buildcache . ``` Attribution: Adapted from Docker Documentation under Apache-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.