Bug: Skaffold tagger ignores Docker target when calculating image tags

[736-c41-2c1-e464fc974]

Environment

• Skaffold version: v2.16.0
• OS: Linux
• Docker version: Docker version 28.2.2, build e6534b4

Description

Skaffold generates identical image tags for different build profiles when the only difference is the Docker build target. This causes duplicate images to be built and pushed, wasting CI/CD resources and creating ambiguity about which variant is deployed.

Steps to Reproduce

1. Create a Dockerfile with multiple targets:

   FROM alpine as base
   
   FROM base as dev
   RUN touch devbuild
   
   FROM base as prod
   RUN touch prodbuild

2. Configure skaffold.yaml with different profiles using different targets:

   apiVersion: skaffold/v4beta11
   kind: Config
   profiles:
     - name: dev
       activation:
         - command: dev
       build:
         tagPolicy:
           inputDigest: {}
         local:
           concurrency: 0
           useBuildkit: true
           tryImportMissing: true
         artifacts:
           - image: out-image
             context: .
             docker:
               dockerfile: Dockerfile
               target: dev
     - name: prod
       activation:
         - command: prod
       build:
         tagPolicy:
           inputDigest: {}
         local:
           concurrency: 0
           useBuildkit: true
           tryImportMissing: true
         artifacts:
           - image: out-image
             context: .
             docker:
               dockerfile: Dockerfile
               target: prod

3. Run skaffold with different profiles:

   $ skaffold build --profile dev --dry-run
   Generating tags...
    - out-image -> out-image:dd0bcd52c53d80e2a77a84d416883ce1804609153de66be26341326f945233c5
   Skipping build phase since --dry-run=true
   
   $ skaffold build --profile prod --dry-run
   Generating tags...
    - out-image -> out-image:dd0bcd52c53d80e2a77a84d416883ce1804609153de66be26341326f945233c5
   Skipping build phase since --dry-run=true

Expected Behavior

Skaffold should generate different image tags for different profiles when they use different Docker build targets, as they produce functionally different images.

Actual Behavior

Skaffold generates identical image tags for both profiles:

out-image:dd0bcd52c53d80e2a77a84d416883ce1804609153de66be26341326f945233c5

Impact

• Ambiguity about which image variant (dev or production) is actually deployed
• Potential for development images to be deployed in production environments
• CI/CD pipelines build and push redundant images

Possible Solution

Modify the checksum calculation in the Skaffold tagger to include the Docker target as part of the input when generating image tags.

[736-c41-2c1-e464fc974]

I found a workaround for this bug. I am now using a customTemplate tagger with {{.INPUT_DIGEST}} that i just prefix with the profile name.

apiVersion: skaffold/v4beta11
kind: Config
profiles:
  - name: dev
    activation:
      - command: dev
    build:
      tagPolicy:
        customTemplate:
          template: "dev-{{.INPUT_DIGEST}}"
      artifacts:
        - image: out-image
          context: .
          docker:
            dockerfile: Dockerfile
            target: dev
  - name: prod
    activation:
      - command: prod
    build:
      tagPolicy:
        customTemplate:
          template: "prod-{{.INPUT_DIGEST}}"
      artifacts:
        - image: out-image
          context: .
          docker:
            dockerfile: Dockerfile
            target: prod