Cache is not used for `docker build .`

[juntyr]

I'm building a Docker dev container in CI, which is used to run some later steps in a pre-defined environment. The Dockerfile is part of the project and changes very infrequently.

In one step, I use ScribeMD/[email protected] to cache the full Docker image. Since the workflow has run before, I get a cache hit and it prints that

Cache restored successfully
docker load --input ~/.docker-images.tar
Loaded image ID: sha256:64b4debbb775ec6f4d258e72c4a44de2f9341b44be1347974e3ddf8db411bb4c

In the next step, I call docker build .. Even though the Dockerfile is unchanged, the build restarts from scratch.

Is there anything else I need to do to use the cached Dockerfile? The cache key includes the hash of the Dockerfile, so it will only have a cache hit if an exact match was already built.

Thanks for your help!