I tried running a custom little webcrawler I run on jruby 9k and just received this exception:

RuntimeError: Could not generate DH keypair
/home/[...]/launcher.rb:291launcher.rb_CLOSURE_16_CLOSURE_17_CLOSURE_18__launcher.rb_CLOSURE_16_CLOSURE_17_17

The stack trace was just 2 lines and pointing on a Thread.new, but not a specific code path.

Some domains that this apparently happened with: cedric-heleinstituut.be, 13iacc.org, ubmstudios.com
I can't seem to reproduce it.

In general, It seems to be a JVM problem. I see comments about this in code over here and a mention over here:
"This is a well-known problem between JVM clients and recent mod_ssl versions, as the DH prime length supported by the JVM is limited."

I am not quite sure if this occurs when using net-http or rjack-async-httpclient, but I thought it might be worth filing an issue in case anyone else runs into it that has a bit more information