kaniko-cache-bug

A bug with the kaniko cache when using globs and multi-stage docker builds.

Repro Steps

1. Build with kaniko with cache on: ./run_in_docker.sh ./Dockerfile . <some-docker-repo>/kaniko-cache-bug:latest true
2. Run ls in the container to see that the file is properly symlinked.

docker pull kaniko-cache-bug:latest && docker run --rm kaniko-cache-bug:latest -l

-rw-r--r--    1 root     root             0 Feb 26 14:33 file-1.txt
lrwxrwxrwx    1 root     root            11 Feb 26 14:33 file.txt -> /file-1.txt

3. Update version.txt to 2
4. Build with kaniko with cache on: ./run_in_docker.sh ./Dockerfile . <some-docker-repo>/kaniko-cache-bug:latest true
5. Run ls in the container to see that the symlink layer was cached and re-used, leading to it pointing at the wrong file.

docker pull kaniko-cache-bug:latest && docker run --rm kaniko-cache-bug:latest -l

-rw-r--r--    1 root     root             0 Feb 26 14:39 file-2.txt
lrwxrwxrwx    1 root     root            11 Feb 26 14:33 file.txt -> /file-1.txt

6. Build with kaniko with cache off: ./run_in_docker.sh ./Dockerfile . <some-docker-repo>/kaniko-cache-bug:latest false
7. Observe that everything works as expected.

docker pull kaniko-cache-bug:latest && docker run --rm kaniko-cache-bug:latest -l

-rw-r--r--    1 root     root             0 Feb 26 14:40 file-2.txt
lrwxrwxrwx    1 root     root            11 Feb 26 14:40 file.txt -> /file-2.txt

Notes

This only occurs with multi-stage builds. a simple version like this will NOT exhibit the bug:

FROM alpine:3.6
COPY version.txt version.txt
RUN touch file-$(cat ./version.txt).txt
RUN ln -s $(find /file-*.txt) /file.txt