kubernetes-maven-plugin automatic pull for cacheFrom image

[davidecavestro]

Forewords
Hi, I open a discussion here as per @manusa suggestion.
I've not provided some reproducible code yet as it would imply pushing a container image on a shared docker registry.

The issue
I've configured the kubernetes-maven-plugin with the cacheFrom config entry in order to reuse some layers from previously produced images.
But it seems that I have to force pulling the image externally in order to have the cacheFrom image in-place and eventually reuse its layers.

Additional details
I leveraged multi-staged builds extracting layers produced by spring boot maven plugin into subfolders, so that when 3rd party deps don't change within the fatjar I reuse the old layer.
I've seen this can be achieved even on ephemeral builders (no docker cache) using cacheFrom to pass the reference to a previously built image (i.e. the image built on the previous run by the CI tool).

I've tried passing to maven CLI -Djkube.docker.imagePullPolicy=Always -Djkube.docker.autoPull=on but they seem to be inifluent, though I have no debugged so far.
OTOH I see a reuse of layers if I manually force the download of the cacheFrom image from outside maven (or even with a maven exec).

Excerpt from Dockerfile
Follows an excerpt from Dockerfile, where the various COPY --from=builder instructions at the bottom potentially benefit from the cacheFrom image (when locally pulled).

# builder stage for fatjar layers extraction
FROM registry.access.redhat.com/ubi8/openjdk-17 as builder
USER root
RUN mkdir -p /inflated
WORKDIR /inflated
COPY maven/jars/app.jar app.jar
# explode the fatjar into a subfolder per layer
RUN java -Djarmode=layertools -jar app.jar extract

# restart from scratch
FROM registry.access.redhat.com/ubi8/openjdk-17

# add layers content
COPY --from=builder /inflated/dependencies/ ./
COPY --from=builder /inflated/spring-boot-loader/ ./
COPY --from=builder /inflated/snapshot-dependencies/ ./
COPY --from=builder /inflated/application/ ./

[manusa]

Hi @davidecavestro,

This has nothing to do with your original question, but while we investigate:

I understand that the end purpose is to be able to reuse some of the intermediate images whilst performing your final build.

Have you tried doing a multilayered (XML/DSL configured) build with a non-fatjar?

In your case, considering the build produces an intermediate version of your jar with the dependencies, it would be something like:

<configuration>
  <images>
    <image>
      <name>${image.repo}/${image.name}:%l</name>
      <build>
        <from>registry.access.redhat.com/ubi8/openjdk-17</from>
        <assembly>
          <targetDir>/home/jboss</targetDir>
          <excludeFinalOutputArtifact>true</excludeFinalOutputArtifact>
          <layers>
            <layer>
              <id>dependencies</id>
              <fileSets>
                <fileSet>
                  <directory>${project.build.directory}/dependencies</directory>
                </fileSet>
              </fileSets>
            </layer>
            <layer>
              <id>loader</id>
              <fileSets>
                <fileSet>
                  <directory>${project.build.directory}/loader</directory>
                </fileSet>
              </fileSets>
            </layer>
            <!-- ... -->
            <layer>
              <id>app</id>
              <fileSets>
                <fileSet>
                  <directory>${project.build.directory}/app</directory>
                </fileSet>
              </fileSets>
            </layer>
          </layers>
        </assembly>
        <ports>
          <!-- Ports to expose in the pod specs -->
          <port>8080</port>
        </ports>
      </build>
    </image>
  </images>
</configuration>