The proxy protocol (https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt) requires that all connections made over a given port include the proxy protocol header. In order to support this, open a configurable second port on Mongos that will accept proxied connections and expect the TCP stream to begin with a proxy protocol header, which we should parse. Mark proxied sessions as such.
- is depended on by
SERVER-58496 Detect connections made via the Proxy Protocol
DRIVERS-1983 Update load balancer tests to support dedicated load balancer port