Can you explain the principle of operation and purpose of the Keepalive mechanism in HAProxy?

The Keepalive mechanism in HAProxy is used to maintain a persistent TCP connection between the client and the server or between the proxy and the backend.

Purpose:

• Reduce the overhead of establishing new connections.
• Improve performance by reusing existing connections.

Working principle:

• When Keepalive is enabled, HAProxy does not close the connection immediately after processing a request but keeps it open for some time.
• If a new request arrives, it can be sent over the already open connection.
• This reduces delays and server load.

Example configuration in HAProxy:

defaults {
    option http-keep-alive
    timeout http-keep-alive 10s
}

Here, option http-keep-alive enables keepalive support, and timeout http-keep-alive sets the timeout for keeping the connection open.