With MongoDB 3.4.15, mongod running with mode: requireSSL, connection attempts without SSL get a nicely informative mongod log message:
2018-05-16T15:38:07.351-0500 D - [conn2] User Assertion: 17189:The server is configured to only allow SSL connections src/mongo/util/net/message_port.cpp 154
In 3.6.4, the log message in this case is:
2018-05-15T14:20:13.067+0000 I NETWORK [conn3] Error receiving request from client: SSLHandshakeFailed: SSLHandshakeFailed. Ending connection from 10.53.32.39:57277 (connection id: 3)
You can see that the 3.6.4 log message is much less informative and clear about the cause of the connection failure. Can we make the log message mention that it's because the server is configured to require SSL connections?