Pulling CNB run image fails when no tag is provided in image name

[scottfrederick]

Attempting to use the builder image gcr.io/buildpacks/builder with the Maven plugin spring-boot:build-image goal or Gradle plugin bootBuildImage task results in an error while pulling the run image gcr.io/buildpacks/gcp/run specified in the builder image metadata.

Example Gradle output:

> Task :bootBuildImage
Building image 'docker.io/library/build-demo:0.0.1-SNAPSHOT'

 > Pulling builder image 'gcr.io/buildpacks/builder:latest' ..................................................
 > Pulled builder image 'gcr.io/buildpacks/builder@sha256:efb5f9b7cd976ab6e5a959f453795863a476878be8e5c20b50db22c8aec1227f'
 > Pulling run image 'gcr.io/buildpacks/gcp/run' ..................................................

> Task :bootBuildImage FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':bootBuildImage'.
> Different digests IDs provided

[scottfrederick]

pack CLI can successfully pull the build and run images:

$ pack build docker.io/library/build-demo --builder gcr.io/buildpacks/builder --path build/libs/build-demo-0.0.1-SNAPSHOT.jar
latest: Pulling from buildpacks/builder
11ab3a0c1a8a: Pull complete
[ ... ]
10badd04bb4a: Pull complete
Digest: sha256:efb5f9b7cd976ab6e5a959f453795863a476878be8e5c20b50db22c8aec1227f
Status: Downloaded newer image for gcr.io/buildpacks/builder:latest
latest: Pulling from buildpacks/gcp/run
11ab3a0c1a8a: Already exists
[ ... ]
dadabbc219f0: Already exists
Digest: sha256:9b3973dd6765f88815318454e337b7f5aacf25cf27f3038be49ef18cf6fce3b1
Status: Downloaded newer image for gcr.io/buildpacks/gcp/run:latest
===> DETECTING
[detector] ERROR: No buildpack groups passed detection.
[detector] ERROR: Please check that you are running against the correct path.
[detector] ERROR: failed to detect: no buildpacks participating
ERROR: failed with status code: 6

This results in both images being pulled with the latest tag:

$ docker images
REPOSITORY                  TAG                 IMAGE ID            CREATED             SIZE
gcr.io/buildpacks/builder   latest              42da5db6a84f        2 hours ago         428MB
gcr.io/buildpacks/gcp/run   latest              ab8975f48640        3 hours ago         111MB

Spring Boot attempts to pull untagged images, which results in multiple run image downloads with different digests after the build failure:

$ docker images
REPOSITORY                  TAG                                        IMAGE ID            CREATED             SIZE
gcr.io/buildpacks/builder   latest                                     42da5db6a84f        3 hours ago         428MB
gcr.io/buildpacks/gcp/run   01a956fa9aad3612c9381cea556898bbcce446a0   ab8975f48640        3 hours ago         111MB
gcr.io/buildpacks/gcp/run   0416777a5a1e15b14db2b915536d59970d03a835   72d0dde704de        45 hours ago        111MB

Forcing the run image tag to latest causes Boot to behave like pack.

[scottfrederick]

The docker pull CLI command defaults the tag to latest. The pack CLI also defaults the tag via the go-containerregistry library. Spring Boot should do the same.