I installed Logstash 5.5.1, 5.5.2 and even 6.0-beta1 bundled with another third party plugin to work with IBM JRE 8. The error "no cipher match" is thrown into logstash-plain.log. Per some deep investigation, this issue is relevant to JRuby-OpenSSL lib packaged with JRuby shipped with Logstash. Luckily, that issue (https://github.com/jruby/jruby/issues/4679) has been fixed in JRuby-OpenSSL 0.9.21, but Logstash was still delivered with old JRuby with old JRuby-OpenSSL version lower than 0.9.21. I checked Logstash 6.0-beta1, it includes Ruby-OpenSSL 0.9.20 gem.
For Logstash 6.0-beta1, the log stack trace is here.
All hosts unavailable, sleeping {:hosts=>["xx.xx.xx.xx"], :e=>#<OpenSSL::SSL::SSLError: no cipher match>, :backtrace=>["org/jruby/ext/openssl/SSLContext.java:506:in ciphers='", "org/jruby/ext/openssl/SSLContext.java:560:inset_params'", "/usr/share/logstash/logstash-core/lib/logstash/patches/stronger_openssl_defaults.rb:18:in new'", "/usr/share/logstash/vendor/local_gems/dee1aeb2/logstash-output-mtlumberjack/lib/mtlumberjack/client.rb:215:inblock in connect'", "org/jruby/ext/thread/Mutex.java:148:in synchronize'", "/usr/share/logstash/vendor/local_gems/dee1aeb2/logstash-output-mtlumberjack/lib/mtlumberjack/client.rb:154:inconnect'", "/usr/share/logstash/vendor/local_gems/dee1aeb2/logstash-output-mtlumberjack/lib/mtlumberjack/client.rb:125:in initialize'", "/usr/share/logstash/vendor/local_gems/dee1aeb2/logstash-output-mtlumberjack/lib/mtlumberjack/client.rb:76:inconnect'", "/usr/share/logstash/vendor/local_gems/dee1aeb2/logstash-output-mtlumberjack/lib/mtlumberjack/client.rb:67:in initialize'", "/usr/share/logstash/vendor/local_gems/dee1aeb2/logstash-output-mtlumberjack/lib/logstash/outputs/mtlumberjack.rb:143:inconnect'", "/usr/share/logstash/vendor/local_gems/dee1aeb2/logstash-output-mtlumberjack/lib/logstash/outputs/mtlumberjack.rb:72:in block in register'", "org/jruby/RubyRange.java:485:ineach'", "/usr/share/logstash/vendor/local_gems/dee1aeb2/logstash-output-mtlumberjack/lib/logstash/outputs/mtlumberjack.rb:71:in register'", "org/jruby/RubyArray.java:1734:ineach'", "/usr/share/logstash/logstash-core/lib/logstash/output_delegator_strategies/legacy.rb:17:in register'", "/usr/share/logstash/logstash-core/lib/logstash/output_delegator.rb:41:inregister'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:376:in register_plugin'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:387:inblock in register_plugins'", "org/jruby/RubyArray.java:1734:in each'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:387:inregister_plugins'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:396:in start_workers'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:321:inrun'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:281:in `block in start'"]}
Is it possible for you to upgrade JRuby with 0.9.21 JRuby-OpenSSL inside Logstash 6.0?