Currently, we can use proxy.process.http.total_client_connections or proxy.process.http.total_incoming_connections to determine the number of TCP connections that have been made from the user_agent to ATS, assuming that HTTP/1.0 or HTTP/1.1 are used.
If SPDY or HTTP/2 are used, these counters will be incremented for each stream not for each network connection.
It would be useful to add counters in the iocore/net area to directly track the number of TCP connections that have been open over time. Right now only the number of currently_open connections are tracked via proxy.process.net.connections_currently_open.
I propose adding two new metrics proxy.process.net.connections_successful_in and proxy.process.net.connections_successful_out