Google Cloud: When the Load Balancer Frontend Hands you an F

If someone hands you an IP:Port of a Google Cloud load balancer, and tells you to connect there with TLS, but all you receive in return is an F (and a few other bytes with none printable characters) on running openssl s_client -connect ... , you might be missing SNI (server name indication). Sadly the other side was not transparent enough to explain in detail which exact type of Google Cloud load…