jenkins/jnlp-agent-jdk8 is broken

[gounthar]

Jenkins and Plugins Version Report

Operating Environment:

• Linux 5.15.153.1-microsoft-standard-WSL2 SMP Fri Mar 29 23:14:13 UTC 2024 x86_64 GNU/Linux
• Debian under WSL2 with Docker version 27.2.0, build 3ab4256

Issue Description

This is a follow-up to jenkins-infra/helpdesk#4364.

The issue stems from a version mismatch in our Docker configuration. While we use a JDK8-based Maven image, the first stage of the build uses an image targeting JDK17:

docker run -it maven:3.6.3-jdk-8-slim bash
root@0e5b337402f5:/# java -version
openjdk version "1.8.0_282"
OpenJDK Runtime Environment (build 1.8.0_282-b08)
OpenJDK 64-Bit Server VM (build 25.282-b08, mixed mode)

docker run -it jenkins/inbound-agent:alpine ash
~ $ java --version
openjdk 17.0.12 2024-07-16
OpenJDK Runtime Environment Temurin-17.0.12+7 (build 17.0.12+7)
OpenJDK 64-Bit Server VM Temurin-17.0.12+7 (build 17.0.12+7, mixed mode)

Steps to Reproduce

docker run -ti --rm jenkins/jnlp-agent-jdk8:latest

Expected Behavior

The command should display the standard agent usage information:

two arguments required, but got []
java -jar agent.jar [options...] <secret key> <agent name>
[... standard help output ...]

Actual Behavior

The command fails with a JNI error:

Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.UnsupportedClassVersionError: hudson/remoting/Launcher has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

Resolution

I will submit a pull request to address this version mismatch issue.