New subject: Setup webRTC via SDP Offer to setup a SIP call INVITE (without websockets)

10 Dec 2021

Hi, 

for having a maintenance mode, I need to implement some sort of draining functionality.
All our clients register via TLS. So I thought, I just answer the next REGISTER of a
client with a 503 and kill the tcp connection afterwards, so they need to open up a new
connection to the loadbalancer in front and end up on a different server.

This is my code:

510         if msg.is_method("REGISTER"):
  1             if KSR.pv.get("$shv(MAINTENANCE_MODE)") == 1:
  2                 KSR.info("In maintenance mode, rejecting registration")
  3                 KSR.hdr.append_to_reply("Retry-After: 2\r\n")
  4                 KSR.sl.sl_send_reply(503, "Draining")
  5                 if KSR.tcpops.tcp_set_connection_lifetime(1) > 0:
  6                     KSR.info("Set Connection lifetime to 1")
  7                 return False

(Side note: msg is some internal class, this is obviously KEMI with python)

So now when I set the MAINTENANCE_MODE var to 1, Kamailio rejects the REGISTER requests,
logs both lines and sends out a 503.

Debug log tells me this:
Dec 10 15:32:10 ifens5 /usr/sbin/kamailio[3851]: DEBUG: tcpops [tcpops.c:229]:
tcpops_set_connection_lifetime(): new connection lifetime for conid=1: 908866403
Dec 10 15:32:21 ifens5 /usr/sbin/kamailio[3855]: DEBUG: <core>
[core/tcp_main.c:4554]: tcpconn_main_timeout(): entering timer for 0x7f759cb26218
(ticks=908866499, timeout=908866499 (0 s), wr_timeout=0 (211631299 s)), write queue: 0
bytes

In tcpdump I can see that the connection does not get closed immediately.

Is there some timer in the tcp stack which cleans up expired connections from time to
time? Can I manipulate how often this timer runs? I couldn't find anything, and
clearly even though I tell Kamailio to close the connection after 1 second, it doesn't
do it.

Thanks for any input.

Regards,
Sebastian

tcp_set_connection_lifetime(1) does not close connection