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Docker Buildkit Cache | All About

Docker is a staple for developers and system administrators when it comes to containerization. Furthermore, it offers BuildKit, which lets users boost the speed, reliability, and security of container builds.

A key feature of BuildKit is its caching mechanism. It caches individual build steps, thus speeding up future builds.

Today, we will take a quick look at BuildKit’s caching system and how it can be used for more efficient containerization.

Before we begin, let’s enable BuildKit’s caching in our Dockerfile. This is done by adding this line to the file:

FROM buildkit

Once BuildKit is activated, it will automatically cache the results of individual build steps.

Furthermore, BuildKit also allows users to specify a location for storing its cache. This can be done by adding this line to our Dockerfile:

ARG BUILDKIT_CACHE=/tmp/buildkit/cache

This line instructs BuildKit to store its cache in the designated /tmp/buildkit/cache directory.

Additionally, sharing the cache between different builds or storing it remotely becomes possible with BuildKit. We can export the cache with this command:

docker buildx build --export-cache type=local,dest=/tmp/buildkit/cache

This exports the cache to the specified /tmp/buildkit/cache directory. Alternatively, we can import the cache by running:

docker buildx build --import-cache type=local,src=/tmp/buildkit/cache

hence, this command imports the cache from the /tmp/buildkit/cache directory.

How Does the BuildKit Cache Work

BuildKit’s caching operates on these principles:

• Layer Caching:

  Docker images consist of layers, each representing a certain instruction or command in the Dockerfile. So, BuildKit caches each layer as it’s built, allowing for reuse in future builds without reconstruction.
• Cache Key:

  A cache key is generated for each build instruction, derived from the input context, including the Dockerfile contents, source code files, and build arguments. This key decides if a particular build layer can be reused from the cache or requires rebuilding due to changes in the input context.
• Dependency Tracking:

  BuildKit intelligently tracks dependencies between build stages and layers. So, if a dependency changes, the cache for affected layers is automatically invalidated, prompting a rebuild of those layers and any dependent layers requiring updates.
• Cache Persistence:

  By default, the BuildKit cache is stored locally on the host machine, allowing for reuse across multiple builds. However, users can configure alternative cache storage solutions, like remote servers or cloud-based services, for enhanced scalability in distributed build environments.
• Cache Management:

  Docker provides commands and options for effective cache management during the image-building process. Options like “–no-cache” force Docker to disregard the cache entirely, rebuilding all layers from scratch. The “–build-arg” option enables passing build arguments that affect the cache key, facilitating the invalidation of specific cache entries.

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Conclusion

In brief, our Support Experts introduced us to Docker Buildkit Cache and how it works.