Multi Stage build not respecting dependency tree

[duxbuse]

Actual behavior
Kaniko builds all stages of a multi stage then only returns the stage specified in the --target declaration.

Expected behavior
Kaniko should only build the stages that the --target has as dependencies.

To Reproduce
Multi stage file like this:

FROM alpine AS builder
  COPY ./shared-content .
  RUN make build

FROM builder AS tester
  COPY testingPackage .
  RUN make test

FROM builder AS deployable
  COPY --from builder application.bin application.bin

I would expect that when building this file with --target = deployable that the test layers would not be built. Partly because they are not used so they will just be thrown away.
Current versions of docker do this dependency mapping to only build required steps.

Triage Notes for the Maintainers

Description	Yes/No
Please check if this a new feature you are proposing
Please check if the build works in docker but not in kaniko
Please check if this error is seen when you use --cache flag
Please check if your dockerfile is a multistage dockerfile

[Akkarine]

Same here. I would also add, that if there is no dependencies at all, kaniko will build all unwanted stages in order which they are declared in Dockerfile till it comes to target. Luckly, if target is the first stage, other stages are not initiates :)

[donmccasland]

Pardon my ignorance, is there a corollary functionality in docker build?

[cvgw]

This may be the same issue as #775

[Akkarine]

Pardon my ignorance, is there a corollary functionality in docker build?

If you use DOCKER_BUILDKIT=1, dependencies resolved correctly.

[frickenate]

Yep, being burned by this. Migrating to GitLab CI with existing multi-stage builds which were using eg. DOCKER_BUILDKIT=1 docker build --target release with the previous build system. Looking at kaniko rather than docker-in-docker, but no support for dependency resolution in multi-stage builds is a killer that has us traveling back in time to having to generate multiple Dockerfiles dynamically? Hell no.