Same error on openjdk11 - looks like it fires long before any compatibility issues
# su -m logstash -c 'sh -c "env JAVA_HOME=/usr/local/openjdk11 /usr/local/logstash/bin/logstash --path.settings /usr/local/etc/logstash -l /var/log/logstash "' Using JAVA_HOME defined java: /usr/local/openjdk11
/usr/local/logstash/logstash-core-plugin-api/lib/logstash-core-plugin-api/version.rb:22: warning: The Psych YAML extension failed to load.
Check your env for conflicting versions of SnakeYAML
See https://github.com/jruby/jruby/wiki/FAQs#why-does-the-psych-yaml-extension-fail-to-load-in-my-environment
[ERROR] 2021-01-07 19:14:35.946 [main] Logstash - java.lang.IllegalStateException: Logstash stopped processing because of an error: (GemspecError)
[!] There was an error while loading `logstash-core-plugin-api.gemspec`: load error: psych -- java.lang.RuntimeException: BUG: we can not copy embedded jar to temp directory
Does it try to require a relative path? That's been removed in Ruby 1.9. Bundler cannot continue.
# from /usr/local/logstash/logstash-core-plugin-api/logstash-core-plugin-api.gemspec:23
# -------------------------------------------
#
> require "logstash-core-plugin-api/version"
#
# -------------------------------------------