This is a meta issue to track some known issues with the Netty 4 implementation:

• port Fixes CORS handling so that it uses the defaults #19522 to Netty 4 Fixes netty4 module's CORS config to use defaults  #19874
• enable advanced leak detection in tests and fail the build if there is a leak Enable Netty 4 advanced leak detection in tests and fail the build if there is a leak #20398
• upgrade to a non-snapshot build of 4.1.4.Final+ of Netty 4 Dependencies: Upgrade to netty 4.1.4 #19689
• set io.netty.noUnsafe to true by default? (probably) Explicitly tell Netty to not use unsafe #19786
• investigate performance