Return caching COPY layers

[YevheniiSemendiak]

Hey folks!
First of all, thank you for your outstanding and such usefull tool!

I have a question to
In #1408 you've removed the logic for caching COPY steps of dockerfiles.

My question is: Is it possible to return it back, at least by enabling it with some flag, such as --cache-copy-layers.

The intent is pretty straightforward - not all users are copying large amounts of data into containers, but only tiny config files, etc. For instance, in my case, the performance degradation is 4x if I compare v1.2.0 vs 1.1.0.

[ByJacob]

I have a similar problem. Each time I copies the same files, he gets different docker layers.

My case:

• create 3 files
  fallocate -l 14M test1.img; fallocate -l 14M test2.img; fallocate -l 14M test3.img
• create Dockerfile

FROM alpine
COPY test1.img /test1.img
COPY test2.img /test3.img
COPY test3.img /test2.img

• pull latest kaniko image

docker pull gcr.io/kaniko-project/executor:debug

• build image

docker run --rm -i -v /home/USERNAME/.docker/config.json:/kaniko/.docker/config.json -v `pwd`:/app -w /app gcr.io/kaniko-project/executor:debug --context /app --destination repository/test-build --cache

• pull image
  docker pull repository/test-build
• build image second time

docker run --rm -i -v /home/USERNAME/.docker/config.json:/kaniko/.docker/config.json -v `pwd`:/app -w /app gcr.io/kaniko-project/executor:debug --context /app --destination repository/test-build --cache

• pull image
  docker pull repository/test-build

Expected:

• nothing download because build docker with the same files

Current:

• download 3 layers when pull second time

[slinstaedt]

Same here. I realized a speedup of 10-20% for copy-heavy images, with the downside of copy-layers not being reused in subsequent builds, even though copied files have the same hash.

The speedup at image build time is mostly negated at runtime, when every cluster node has to pull gigs of meant to be cached layers, instead of the one build job, pulling them once.

[tejal29]

Thank you folks for the feedback. It is possible to bring this feature back with a flags. I will work on this week before Friday's release.