ProposaL: Align jib-maven-plugin configuratoin with jib-gradle-plugin. (

#236)

proposals/maven_configuration_v2.md

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+# Proposal: Align `jib-maven-plugin` configuration with `jib-gradle-plugin`
+
+## Motivation
+
+`jib-gradle-plugin` introduced a different configuration schema from `jib-maven-plugin`. This schema has many benefits over the original `jib-maven-plugin` configuration. Therefore, to maintain consistency between the two plugins, the `jib-maven-plugin` configuration should be updated to be more similar to the `jib-gradle-plugin` configuration.
+
+## Goals
+
+- Have `jib-maven-plugin` configuration be as similar to `jib-gradle-plugin` configuration as possible
+
+## Non-Goals
+
+- Maintain compatibility with older versions of `jib-maven-plugin` (we are still in alpha)
+
+## Current Configuration Schema
+
+The current `jib-maven-plugin` configuration looks like:
+
+```xml
+<configuration>
+  <from>openjdk:alpine</from>
+  <registry>localhost:5000</registry>
+  <repository>my-image</repository>
+  <tag>built-with-jib</tag>
+  <credHelpers>
+    <credHelper>osxkeychain</credHelper>
+  </credHelpers>
+  <jvmFlags>
+    <jvmFlag>-Xms512m</jvmFlag>
+    <jvmFlag>-Xdebug</jvmFlag>
+    <jvmFlag>-Xmy:flag=jib-rules</jvmFlag>
+  </jvmFlags>
+  <mainClass>mypackage.MyApp</mainClass>
+  <enableReproducibleBuilds>true</enableReproducibleBuilds>
+  <imageFormat>OCI</imageFormat>
+</configuration>
+```
+
+And the current `jib-gradle-plugin` configuration looks like:
+
+```groovy
+jib {
+  from {
+    image = 'openjdk:alpine'
+  }
+  to {
+    image = 'localhost:5000/my-image/built-with-jib'
+    credHelper = 'osxkeychain'
+  }
+  jvmFlags = ['-Xms512m', '-Xdebug', '-Xmy:flag=jib-rules']
+  mainClass = 'mypackage.MyApp'
+  reproducible = true
+  format = 'OCI'
+}
+```
+
+## Desired Configuration Schema
+
+Therefore, the desired `jib-maven-plugin` configuration should look like:
+
+```xml
+<configuration>
+  <from>
+    <image>openjdk:alpine</image>
+  </from>
+  <to>
+    <image>gcr.io/my-gcp-project/my-app</image>
+    <credHelper>gcr</credHelper>
+  </to>
+  <jvmFlags>
+    <jvmFlag>-Xmy:flag=jib-rules</jvmFlag>
+  </jvmFlags>
+  <mainClass>mypackage.MyApp</mainClass>
+  <reproducible>true</reproducible>
+  <format>OCI</format>
+</configuration>
+```
+
+The key changes are:
+
+- Removes `registry`, `repository`, and `tag` - these are now defined as one field `to.image`.
+- Adds an image configuration object that takes:
+  - `to` - the image reference, and
+  - `credHelper` - the credential helper for that image
+- The image configuration object configures both the base image (`from`) and the target image (`to`).
+- `enableReproducibleBuilds` is renamed to `reproducible`.
+- `imageFormat` is renamed to `format`.
+
+## Implementation Details
+
+1. Change `BuildConfiguration` to individual `credHelper`s for the base and target images, not as a list.
+2. Change the `BuildImageMojo` (and `DockerContextMojo`) schema.
+  - The only required field now is `to.image`.