Cloud Native Buildpacks (CNB) use a five-phase lifecycle to transform source code into secure container images. But if you drop standard buildpack commands into a modern, ephemeral CI/CD pipeline like GitHub Actions or GitLab CI, your builds will be slow.
Ephemeral runners start with a blank slate. They lack a local Docker cache. On every run, your buildpacks download the language runtimes and every application dependency from the internet.
Fortunately, Cloud Native Buildpacks offer reliable caching mechanisms. By using the Restore phase, buildpacks can reuse unchanged dependency layers from previous builds to skip unnecessary downloads. Here are two practical ways to drop your pipeline times from minutes to seconds.
If you develop locally or use persistent CI nodes, the fastest approach is to share the host machine's cache with the build container.
For example, a Java developer already has required JARs sitting in the local ~/.m2 or ~/.gradle directories. A buildpack container runs in isolation and cannot see these files by default. You can expose them using the --volume flag.
# For Maven
pack build my-java-app \
--builder paketobuildpacks/builder-jammy-base \
--volume $HOME/.m2:/home/cnb/.m2:rw
# For Gradle
pack build my-java-app \
--builder paketobuildpacks/builder-jammy-base \
--volume $HOME/.gradle:/home/cnb/.gradle:rwThe /home/cnb/ path maps to the non-root user that executes the buildpack inside the container. The tag allows the buildpack to read your existing cache and save new dependencies back to your host machine for the next build.
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:rwVolume mounting fails in Kubernetes pipelines where the pod dies after the build finishes. To preserve layers across different host machines, you need a Cache Image.
A cache image takes the output of the buildpack's cache directory, like downloaded node_modules, and pushes it to your registry as an OCI image. On the next run, the restorer phase pulls this image, extracts the metadata, and skips downloading unchanged dependencies.
Use the --cache-image flag alongside the --publish flag to push the output directly to your registry.
pack build registry.example.com/my-org/my-node-app:latest \
--builder paketobuildpacks/builder-jammy-base \
--publish \
--cache-image registry.example.com/my-org/my-node-app-cache:latestRun 1 (Cache Miss): The pipeline runs. The cache image is empty, so the buildpack downloads all packages. During the Export phase, it uploads the cache layer to the registry.
Run 2 (Cache Hit): A developer changes one line of code. The pipeline spins up a fresh runner. The lifecycle pulls the cache image, sees the lockfile is unchanged, and instantly restores the dependencies. It completely bypasses the install execution.
Sometimes caches get corrupted. You might also want a completely fresh build to ensure production readiness. You do not need to manually delete your cache images from the registry. Simply pass the --clear-cache flag to the pack CLI. This instructs the lifecycle to ignore previous caches and rebuild everything from scratch.


