Jib JVM Flags Extension

A Jib maven extension outputs the configured jvmFlags into the /app/jib-jvm-flags-file file, allowing a custom entrypoint to access these flags.

When a custom entrypoint is used, Jib ignores the jvmFlags settings. This extension ensures that the configured jvmFlags are accessible even in such scenarios:

• For Java 11+:

  java @/app/jib-jvm-flags-file -cp @/app/jib-classpath-file @/app/jib-main-class-file

• With shell:

  java $(cat /app/jib-jvm-flags-file) -cp $(cat /app/jib-classpath-file) $(cat /app/jib-main-class-file)

Note: Requires Java 11 or newer

Usage

To use the Jib JVM Flags extension in your project, configure the jib-maven-plugin as follows:

<plugin>
  <groupId>com.google.cloud.tools</groupId>
  <artifactId>jib-maven-plugin</artifactId>
  <version>${jib-maven-plugin.version}</version>
  <configuration>
    <pluginExtensions>
      <pluginExtension>
        <implementation>tw.com.softleader.cloud.tools.jib.maven.JvmFlagsExtension</implementation>
      </pluginExtension>
    </pluginExtensions>
  </configuration>
  <dependencies>
    <dependency>
      <groupId>tw.com.softleader.cloud.tools</groupId>
      <artifactId>jib-jvm-flags-extension-maven</artifactId>
      <version>${jib-jvm-flags-extension-maven.version}</version>
    </dependency>
  </dependencies>
</plugin>

Customizing Entrypoint with Java Command

To customize the entrypoint using a direct Java command, for example:

<configuration>
  <container>
    <jvmFlags>
      <jvmFlag>-XshowSettings:vm</jvmFlag>
      <jvmFlag>-Xdebug</jvmFlag>
    </jvmFlags>
    <entrypoint>java,@/app/jib-jvm-flags-file,-cp,@/app/jib-classpath-file,@/app/jib-main-class-file</entrypoint>
  </container>
  <pluginExtensions>
    <pluginExtension>
      <implementation>tw.com.softleader.cloud.tools.jib.maven.JvmFlagsExtension</implementation>
    </pluginExtension>
  </pluginExtensions>
</configuration>

Customizing Entrypoint Using a Shell Script

You can also use a shell script to launch your app:

#!/bin/bash
set -e

# Perform any necessary steps before starting the JVM,
# such as setting JVM options or preparing the environment
export JAVA_TOOL_OPTIONS="-Xmx1g"

exec java $(cat /app/jib-jvm-flags-file) \
  -cp $(cat /app/jib-classpath-file) \
  $(cat /app/jib-main-class-file) \
  "$@"

And then configure the plugin to use this script:

<configuration>
  <container>
    <jvmFlags>
      <jvmFlag>-XshowSettings:vm</jvmFlag>
      <jvmFlag>-Xdebug</jvmFlag>
    </jvmFlags>
    <entrypoint>sh,/entrypoint.sh</entrypoint>
  </container>
  <extraDirectories>
    <paths>
      <path>
        <from>.</from>
        <includes>entrypoint.sh</includes>
      </path>
    </paths>
  </extraDirectories>
  <pluginExtensions>
    <pluginExtension>
      <implementation>tw.com.softleader.cloud.tools.jib.maven.JvmFlagsExtension</implementation>
    </pluginExtension>
  </pluginExtensions>
</configuration>

Extension Properties

You can further customize the extension with the following properties:

<pluginExtension>
  <implementation>tw.com.softleader.cloud.tools.jib.maven.JvmFlagsExtension</implementation>
  <properties>
    <!-- Skip if no jvmFlags specified, Default: false -->
    <skipIfEmpty>true</skipIfEmpty>
    <!-- The separator character to use to join jvmFlags, Default: " " (space) --> 
    <separator>,</separator>
    <!-- Set the output file name in container, Default: jib-jvm-flags-file --> 
    <filename>my-jvm-flags-file</filename>
    <!-- Set the output file permissions in container, Default: 644 --> 
    <mode>666</mode>
  </properties>
</pluginExtension>