Avoid to run on JDK < 21

[andsel]

Release notes

Checks that the minimum required JDK is verified. Avoid to run on JDK below 21.

What does this PR do?

Updates runner.rb to do a JDK version check. In case the recognised JDK version is below 21 logs an error message and exit.
At the same time permit to manually force the check , reading the logstash.jdk.force from JVM options. Set -Dlogstash.jdk.force=true either in config/jvm.options or LS_JAVA_OPTS to run Logstash. If this condition is met a warn message is logged and execution proceed as usual.

Why is it important/What is the impact to the user?

A user should always use verified and supported JDK version. Starting from 8.19.19 the JDK 17 is deprecated and the suggested (and bundled) one is JDK 21. If the user customized his Java, setting LS_JAVA_HOME, to an unsupported version, Logstash stops. This can be manually forced setting -Dlogstash.jdk.force=true in either LS_JAVA_OPTS or in the config/jvm.options.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files (and/or docker env variables)
• [ ] I have added tests that prove my fix is effective or that my feature works

Author's Checklist

• [ ]

How to test this PR locally

Verify that with unsupported JDK version, Logstash logs an error and refuse to start.

LS_JAVA_HOME="/path/to/java/17.0.19-tem" bin/logstash -e "input{stdin{}} output{stdout{}}"

Verify that with unsupported JDK version AND manually forcing it, Logstash logs a warning and start.

LS_JAVA_HOME="/path/to/java/17.0.19-tem" LS_JAVA_OPTS="-Dlogstash.jdk.force=true"  bin/logstash -e "input{stdin{}} output{stdout{}}"

Related issues

• Closes Prevent Logstash from starting by default if JDK17 is detected. #19237

Logs

Example execution avoidance:

Using LS_JAVA_HOME defined java: /Users/andreaselva/.sdkman/candidates/java/17.0.19-tem.
Sending Logstash logs to /Users/andreaselva/workspace/logstash_andsel/logs which is now configured via log4j2.properties
[2026-07-16T11:24:39,161][INFO ][logstash.runner          ] Log4j configuration path used is: /Users/andreaselva/workspace/logstash_andsel/config/log4j2.properties
[2026-07-16T11:24:39,164][ERROR][logstash.runner          ] Starting from Logstash 8.19.19 the minimum required version of Java is 21; your Java version from `/Users/andreaselva/.sdkman/candidates/java/17.0.19-tem` is `17` and does not meet this requirement. Running Logstash with the bundled JDK is recommended. The bundled JDK has been verified to work with each specific version of Logstash, and generally provides best performance and reliability. If you have compelling reasons for using your own JDK (organizational-specific compliance requirements, for example), the version you supply with LS_JAVA_HOME must meet the minimum requirements.
[2026-07-16T11:24:39,169][FATAL][org.logstash.Logstash    ] Logstash stopped processing because of an error: (SystemExit) exit
org.jruby.exceptions.SystemExit: (SystemExit) exit
	at org.jruby.RubyKernel.exit(org/jruby/RubyKernel.java:928)
	at org.jruby.RubyKernel.exit(org/jruby/RubyKernel.java:887)
	at Users.andreaselva.workspace.logstash_andsel.lib.bootstrap.environment.<main>(/Users/andreaselva/workspace/logstash_andsel/lib/bootstrap/environment.rb:90)

Example with manual force:

[2026-07-16T11:19:00,700][INFO ][logstash.runner          ] Log4j configuration path used is: /Users/andreaselva/workspace/logstash_andsel/config/log4j2.properties
[2026-07-16T11:19:00,703][WARN ][logstash.runner          ] Starting from Logstash 8.19.19 the minimum required version of Java is 21; your Java version from `/Users/andreaselva/.sdkman/candidates/java/17.0.19-tem` is `17` and does not meet this requirement. You have selected to force the execution with unsupported Java version, and could generate unexpected malfunctions. Running Logstash with the bundled JDK is recommended. The bundled JDK has been verified to work with each specific version of Logstash, and generally provides best performance and reliability. If you have compelling reasons for using your own JDK (organizational-specific compliance requirements, for example), the version you supply with LS_JAVA_HOME must meet the minimum requirements.
[2026-07-16T11:19:00,704][WARN ][logstash.runner          ] The use of JAVA_HOME has been deprecated. Logstash 8.0 and later ignores JAVA_HOME and uses the bundled JDK. Running Logstash with the bundled JDK is recommended. The bundled JDK has been verified to work with each specific version of Logstash, and generally provides best performance and reliability. If you have compelling reasons for using your own JDK (organizational-specific compliance requirements, for example), you can configure LS_JAVA_HOME to use that version instead.
[2026-07-16T11:19:00,704][INFO ][logstash.runner          ] Starting Logstash {"logstash.version"=>"8.19.19", "jruby.version"=>"jruby 9.4.15.0 (3.1.7) 2026-06-08 6114208a31 OpenJDK 64-Bit Server VM 17.0.19+10 on 17.0.19+10 +indy +jit [arm64-darwin]"}
[2026-07-16T11:19:00,704][INFO ][logstash.runner          ] JVM bootstrap flags: [-Xms1g, -Xmx1g, -Djava.awt.headless=true, -Dfile.encoding=UTF-8, -Djruby.compile.invokedynamic=true, -XX:+HeapDumpOnOutOfMemoryError, -Djava.security.egd=file:/dev/urandom, -Dlog4j2.isThreadContextMapInheritable=true, -Dlogstash.jdk.force=true, -Djruby.regexp.interruptible=true, -Djdk.io.File.enableADS=true, --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED, --add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED, --add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED, --add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED, --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED, --add-opens=java.base/java.security=ALL-UNNAMED, --add-opens=java.base/java.io=ALL-UNNAMED, --add-opens=java.base/java.nio.channels=ALL-UNNAMED, --add-opens=java.base/sun.nio.ch=ALL-UNNAMED, --add-opens=java.management/sun.management=ALL-UNNAMED, -Dio.netty.allocator.maxOrder=11]

[github-actions]

🤖 GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)
• run exhaustive tests : Run the exhaustive tests Buildkite pipeline.

[donoghuc]

run exhaustive tests

[donoghuc]

Will we need to adjust jdk matrix buildkite tests? For 8.19 we seem to be testing against java 17, i think that we will need to either do the override for now in test? Or should we just stop testing on 17 now?

[andsel]

#19291 already contains a backport of #16464 that update the CI moving from JDK17 to JDK21.

If we run the exhaustive test on JDK17, this PR should fail (I would expect) because it exist the Logstash run if JDK 17 is detected 🤔

[andsel]

I answered myself, the acceptance tests, run the LS package, which bundles JDK 21 on 8.19, so JDK 17 is used to execute Gradle etc but then when LS process is spawn it runs the JDK 21.

[infra-vault-gh-plugin-prod]

💚 Build Succeeded

• Buildkite Build
• Commit: 88d413b

History

• 💛 Build #5079 was flaky 9ee19a4
• 💚 Build #5078 succeeded de7eec1

cc @andsel

[andsel]

The execution before 88d413b showed the problme: https://buildkite.com/elastic/logstash-linux-jdk-matrix-pipeline/builds/812.

@donoghuc fixed please give it another eye if you can.