Hello,
(Sorry for cross-posting to -users and -dev; not really sure where this post belongs most.)
A few days ago, I ran into an issue with a Kamailio server being somewhat unresponsive, during moderate call volume, on account of a down rtpproxy--the only rtpproxy in the set. This is rtpproxy classic, not ngcp-mediaproxy-ng.
Rtpproxy was not actually engaged on any of the initial INVITEs going through the server; the server is configured to invoke it conditionally based on a setting, and the setting was not set for any endpoints. rtpproxy_manage() was never called.
However, I call unforce_rtp_proxy() unconditionally in my config when handling CANCELs, reasoning that it can't do any harm if rtpproxy_manage() was not called before[1].
Nevertheless, it seemed to be the case that this situation was clogging up SIP worker threads, because some SIP messages were definitely dropped. Periodic log messages about inability to reach the rtpproxy were echoed as well. This problem cleared up almost immediately when the rtpproxy instance was restored into service.
This raised some questions in my mind about the relationship between rtpproxy management and SIP worker thread utilisation. I assume it was my indiscriminate unforce_rtp_proxy() calls that were actually clogging up the worker threads, right? If so, why? I figured that in the unforce_rtp_proxy() case, the rtpproxy module simply sends fire-and-forget UDP messages down the UDP control socket without any sort of blocking for acknowledgement, since in this case the call must be released on the rtpproxy side without doing any rewriting of SDP on the Kamailio side (unlike in the case where rtpproxy is engaged). Thus, there should be no need to wait for ports to substitute into the message. Or is the same response-wait mechanism used regardless, even in the unforce_rtp_proxy() case, for programmatic reasons?
More broadly, is there any way that this scenario can be prevented? In other words, is there a way to work around an outage of all rtpproxies in the set without tying up workers, or at least tying them up less severely?
Thanks!
-- Alex
[1] Is this a reasonable assumption?
The reason I do this is that I don't see a way to find out if rtpproxy was engaged from the body of a CANCEL message. I do check for a ;proxy_media RR parameter when handling BYEs, but since a CANCEL is not an in-dialog request, I'm not sure what to do except to call unforce_rtp_proxy()/rtpproxy_manage() indiscriminately, without resorting to storing state in htable or other complications I don't want.