Javascript Strategies are Broken in Java 17

[boaz-wiesner]

It seems that in Java 17 the javascript runtime is no longer built in. When a javascript strategy, such as the overlord affinity strategy, is evaluated at runtime, the strategy fails to run (and the task fails), saying that "engine" is null.

druid/indexing-service/src/main/java/org/apache/druid/indexing/overlord/setup/JavaScriptWorkerSelectStrategy.java

Line 64 in 5fcf420

final ScriptEngine engine = new ScriptEngineManager().getEngineByName("javascript");

This may be expected behavior, and may be out of context for Druid to solve, however as Java 17 is the recommended runtime, there should probably be documentation on how to load the required libraries to allow Javascript functionality.

In the case that this is a distribution based issue, we're using openjdk-17-jre-headless.

Either way, for those looking for a quick workaround, like we were, reverting the overlord back to Java 8 works.

[jakubmatyszewski]

There was a PR regarding this issue: #14795 but it's stale and in current form it would introduce backwards incompatible implementation for users still runing JDKs before version 11.

However I 100% agree that it would be nice if there was a clear declaration on this matter from Druid maintainers.