What's the exact meaning of "session" in haproxy?

Question

When I open the haproxy statistics report page of my http proxy server, I saw something like this:

Cum. connections:   280073
Cum. sessions   :   3802
Cum. HTTP requests: 24245

I'm not using 'appsession' and any other cookie related command in the configuration. So what's 'session' means here?

I guess haproxy identify http session by this order:

1. Use cookie or query string if it's exists in the configuration.
2. Use SSL/TLS session.
3. Use ip address and TCP connection status.

Am I Right?

Answer 1

I was asking myself the very same question this morning.

Searching through http://www.haproxy.org/download/1.5/doc/configuration.txt I came accross this very short definition (hidden in a parameter description) :

A session is a connection that was accepted by the layer 4 rules.

In your case, you're obviously using Haproxy as a layer7/HTTP loadbalancer. If a session is a TCP connection, due to client-side / frontend Keep-Alive, it's normal to have more HTTP reqs than sessions.

Then I guess the high connection number shows that a lot of incoming connections were rejected even before being considered by the HTTP layer. For instance via IP-based ACLs.

As a far as I understand, the 'session' word was introduced to make sure two different concepts were not mixed :

• a (TCP) connection : it's a discrete event
• a (TCP) session : it's a state which tracks various metadata and has some duration; most importantly Haproxy workload (CPU and memory) should be mostly related to the number of sessions (both arrival rate and concurrent number)