23 Dec
2024
23 Dec
'24
11:51 a.m.
One additional thought -- sorry for the numerous messages:
This discussion has got a little too academic. When talking about concurrency, it's
important to ask what the workload actually is and how parallelisable it is.
1) All these async tricks are most useful when you have a busy Kamailio server that does
lots of different kinds of things. Freeing up worker processes becomes an important
objective, because not blocking them with these requests allows them to handle those
requests and those other replies.
2) The other important consideration is locking: how much are shared-memory structures
(transaction state, dialog state, htables, etc) being accessed by multiple worker
processes?
These issues are typical of Kamailio-based multiservice SIP gateways that perform
functions like call routing, registration, presence, etc. all in one system.
Purpose-built redirect servers that query an HTTP API have a trivial and one-track
workload. They receive an INVITE, it's allocated to a worker, the worker goes and
bangs on an HTTP server, gets a response, and sends it back to the callee. There are no
other requests to juggle, save for the incidental OPTIONS ping maybe, there are no SIP
replies to process and relay, and nothing else to do except to absorb ACKs (if the
redirects are sent statefully). Along the way, vanishingly little is being accessed apart
from transaction memory (if stateful), and concurrent accesses to that are fast because
the locks are pretty granular.
Thus, this type of workload doesn't benefit from general-purpose throughput
optimisations much. The proper approach, using whichever HTTP client module, is to spin up
as many child processes as can be spun up without diminishing returns, and just dedicating
them to that singular function while studiously avoiding lockable shared data (e.g.
htable). This keeps all the cars mostly in their own lanes, and the success or failure of
that per se will dictate throughput.
-- Alex
On Dec 23, 2024, at 11:25 am, Alex Balashov
<abalashov(a)evaristesys.com> wrote:
PS. A key selling point of this is that if the TCP client crashes or becomes unavailable,
the transaction just times out after a while, instead of any Kamailio worker processes
shitting themselves or blocking because they're unable to connect to something.
There's nothing to connect to.
This alone sold me. Once you go EVAPI, you can't go back.
-- Alex
--
Alex Balashov
Principal Consultant
Evariste Systems LLC
Web: https://evaristesys.com
Tel: +1-706-510-6800
On Dec 23, 2024, at 11:23 am, Alex Balashov
<abalashov(a)evaristesys.com> wrote:
--
Alex Balashov
Principal Consultant
Evariste Systems LLC
Web: https://evaristesys.com
Tel: +1-706-510-6800
On Dec 23, 2024, at 10:56 am, Ben Kaufman via
sr-users <sr-users(a)lists.kamailio.org> wrote:
This came off a bit more harsh than I intended. I think I understand the advantage of
EVAPI in that it can initiate a command to Kamailio (thus Kamailio doesn't need to
hold the thread, possibly it doesn't need to store the message even), but it would
still be nice to have a higher level overview of how this would be achieved. Not even
example code, but more a base architecture explanation / diagram of the flow.
It's probably not complicated enough to warrant a diagram.
1) EVAPI server is initialised:
loadmodule "evapi"
modparam("evapi", "workers", 3)
modparam("evapi", "bind_addr", "xxx:10399")
2) TCP client connects to this socket when it becomes available;
2) Kamailio receives request and serialises it (e.g. JSON), embedding the transaction ID
and label in whatever serialisation structure is used, then emits it on the EVAPI bus,
e.g.
evapi_async_relay("invite_request:$T(id_index):$T(id_label):$(var(data){s.encode.base64})");
3) TCP client reads this package off the wire; the built-in netstring support is ideal.
It then processes it, generates a response, serialises it, and puts it back on the wire.
Vitally, the $T(id_index) and $T(id_label) are embedded in the response, allowing Kamailio
to resume the transaction:
4) Kamailio receives this message in $evapi(msg), in this event_route, and resumes the
transaction into route[RESUME]:
event_route[evapi:message-received] {
...
jansson_get("tm_trans.tm_index", "$evapi(msg)",
"$var(t_index)");
jansson_get("tm_trans.tm_label", "$evapi(msg)",
"$var(t_label)");
t_continue("$var(t_index)", "$var(t_label)", "RESUME");
...
}
5) In route[RESUME], INVITE processing continues as normal, enlightened by anything else
that was deserialised out of $evapi(msg).
EVAPI is my favourite Kamailio module, and the only way I interface with outside
services, when it's up to me.
-- Alex
--
Alex Balashov
Principal Consultant
Evariste Systems LLC
Web: https://evaristesys.com
Tel: +1-706-510-6800