[JAMES-3613] Avoid DNS resolution for protocol MDC context

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.4.0, 3.5.0, 3.6.0
• Fix Version/s: 3.7.0
• Component/s: IMAPServer, POP3Server, SMTPServer
• Assignee: Unassigned
• Reporter: Benoit Tellier
• Created: 14/Jul/21 01:02
• Updated: 12/Aug/21 06:55
• Resolved: 12/Aug/21 06:55

Description

On gitter:

Running into an odd issue after an application restart. (James 3.4.0 running in SpringBoot application). Was working fine, but now seem to be getting hung, or at least slow threads, on java.net.Inet6AddressImpl.getHostByAddr as called by org.apache.james.protocols.netty.ProtocolMDCContext.retrieveHost(ProtocolMDCContext.java:55). My environment is Java 11, on Amazon Linux 2, on EC2. 

https://gist.github.com/devondragon/8ec7424a48dc843338443b0b98356289

this seems to have been caused by too many incoming SMTP connections. Showed up in an odd way, but by decreasing the inbound connections this issue has stopped happening...

Likely some rate limit on DNS resolution.

Proposal: switch from `getHostName` to `getHostString` to prevent the DNS resolution.

Issue Links

• links to: GitHub Pull Request #540