Created from https://groups.google.com/d/msgid/mongodb-user/648dde1f-79ef-4056-85a4-7eaa2fcf8178%40googlegroups.com. The startup warning
** WARNING: No SSL certificate validation can be performed since no CA file has been provided ** Please specify an sslCAFile parameter.
should actually read
** WARNING: No client certificate validation can be performed since no CA file has been provided ** Please specify an sslCAFile parameter.
As long as the user has specified a valid SSLPEMKeyFile, TLS is working correctly and the client should be able to validate the server's certificate, and that is a common use case.