'could not parse reference' for cached builds with UPPERCASE stage names

[dinvlad]

Actual behavior
Multi-stage builds fail with

error building image: getting stage builder for stage 2: could not parse reference

if --cache=true and stage names contain UPPERCASE letters.

Expected behavior
Cached builds should succeed irregardless of character case in stage names.

To Reproduce
Steps to reproduce the behavior:

1. Set up CloudBuild builds based on https://github.com/broadinstitute/kaniko-stage-naming-bug
   (the builds are trigged with --cache=true).
2. The build should fail with

   WARN[0011] Error while retrieving image from cache: could not parse reference 
   error building image: getting stage builder for stage 2: could not parse reference
   

Stage 2 is the one trying to use the previous stage named with uppercase letters (see below). The build succeeds for stage 1, which refers to stage 0 with only lowercase letters and _.

Additional Information

• Dockerfile

  FROM alpine as base_stage
  
  RUN echo base_stage
  
  
  FROM base_stage as BUG_stage
  
  RUN echo BUG_stage
  
  
  FROM BUG_stage as final_stage
  
  RUN echo final_stage

• Build Context
  Does not apply.
• Kaniko Image (fully qualified with digest)
  gcr.io/kaniko-project/executor@sha256:a3e1a4ac0fc9625ce0eb2f74094e4e801cb1164c93a1dd6b8d2306f6efee7d9a

[faiq]

I've experienced this issue not only with stage build names but building docker images that start with an all caps from image.

ie:

FROM CENTOS
RUN ls 

fails for me.

[cvgw]

FROM CENTOS
RUN ls

I don't believe CENTOS is a valid image name. AFAIK only lowercase letters, _, and - are allowed.

Looking into the issue with stage aliases

[cvgw]

I believe the issue is with this line

kaniko/pkg/dockerfile/dockerfile.go

Line 97 in 00a01f9

if stage.Name == stages[currentStage].BaseName {

as stage.Name will be all lowercase while stages[currentStage].BaseName will be the original case

like such

stage name bug_stage current stage idx 2 current stage base name BUG_stage

[cvgw]

also here

kaniko/pkg/dockerfile/dockerfile.go

Line 252 in 00a01f9

if stage.BaseName == stages[index].Name {

[cvgw]

I wonder if this line also should be updated

kaniko/pkg/dockerfile/dockerfile.go

Line 197 in 00a01f9

if stage.Name == target {