It would seem the best solution is to use something that can use the SIP 
protocol for making routing decisions - for example, Kamailio acting as a 
stateless load balancer, either as a replacement for your load balancer or 
between your layer4 load balancer (just doing pure round-robin of received 
packets) and your stateful SIP endpoint.  A simple deterministic algorithm 
(like modulo over a hash of the called) will ensure that a CANCEL will reach 
the same stateful SIP endpoint as the INVITE.



-----Original Message-----
From: Alex Balashov via sr-users <[email protected]>
Sent: Tuesday, October 10, 2023 12:31 PM
To: Kamailio (SER) - Users Mailing List <[email protected]>
Cc: Alex Balashov <[email protected]>
Subject: [SR-Users] Re: Using DMQ to sync the TM module.

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But I should add: do you actually need state? All replies can be routed back 
based on the content of SIP headers alone -- that is to say, statelessly. Most 
simple load balancers remain stateless for this very reason.

> On 10 Oct 2023, at 13:09, Alex Balashov <[email protected]> wrote:
>
> There is not.
>
>> On 10 Oct 2023, at 12:50, Michel Pelletier via sr-users 
>> <[email protected]> wrote:
>>
>> Hi,
>>
>> I have 2 kamailio instances behind a load balancer.  The problem I have is 
>> that the load balancer can only track TCP connections, but not UDP.  So one 
>> Kamailio instance might send a request using UDP, while the corresponding 
>> UDP reply arrives on the other.  This doesn't play well with the (stateful) 
>> TM module.  Is there a way to synchronize the TM module accross Kamailio 
>> instances using DMQ?
>>
>> Cheers,
>>
>> Michel Pelletier
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> --
> Alex Balashov
> Principal Consultant
> Evariste Systems LLC
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--
Alex Balashov
Principal Consultant
Evariste Systems LLC
Web: https://evaristesys.com/
Tel: +1-706-510-6800

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