Each container built in a FoundriesFactory will publish the build cache layers to our private registry, hub.foundries.io. Subsequent builds will pull from this cache, importing it for the current build. This provides efficient incremental container builds for our FoundriesFactory users. Exporting and importing these build cache layers uses the built-in features of Docker Buildx.
While the cache is very helpful, there are a few things to note:
- The build cache for each container image is branch specific
- It is architecture specific
- It can be invalidated for a few reasons, such as source files changing or a base image update.
When trying to understand why the cache has been invalidated, there are not any
tools that can assist. That said, in a FoundriesFactory each container build
will automatically use the docker build context to create a list of md5sums of all
source files used in the build. Each Compose Apps will generate an artifact
<compose-app-name>-md5sum.txt, which then can be used to
diff from build to build to assist in understanding what files may
have changed, and how that effects the caching. Generally, each line in your
creates it’s own image layer, and a corresponding cache layer. If source files change,
or any direct modification to the
Dockerfile occurs, it will invalidate the cache from
that point forward. With the importance of these concepts towards building Compose Apps,
it is recommended to read the documentation related to Dockerfile best practices.