[SR-Users] Failover with SRV records

[Iñaki Baz Castillo]

2010/11/29 marius zbihlei <marius.zbihlei at 1and1.ro>:
>> AFAIR using raw sockets checking ICMP notifications would be possible
>> (not yet implemented, but possible as I remember from a thread with
>> Andrei).
>>
>
> Possible, but not easily implementable, as ICMP Host unreachable are sent
> asynchronously from the kernel. Also the current sendto() call does not
> guarantee delivery on all Unixes (Linux should be fine),  connected UDP
> sockets are to be used instead.
>>
>> IMHO this would be very useful because if a UDP port is unreachable
>> and there is a ICMP notification about it, the proxy should generate
>> an internal 503 (transport error) rather than a 408 (fr_timer
>> timeout).
>>
>>
>
> Well, this means that we should disable dns_failover (or equivalents)
> completely and handle ICMP errors in failure_route blocks(just test if the
> transaction issued a 503).

Humm, I expect that when discovering the destination (DNS SRV) N
branches should be generated in serial forking fashion in case there
are various priorities in the received response, am I wrong?


> If I recall RFC 3263 , this would mean another
> server discovery (as the new request generates a new transaction) so again
> there is the possibility that the broken host is selected. If we use this
> dns fallback(IMHO this is a nice feature- I personally rely on this) how do
> we decide to generate a 503 ?

503 should be the final winning response in case all the branches fail.


> If the host is already a IP address, that it would be ok to send a 503, as
> no DNS failover is possible.

Yes.


> Ideas?

I think that what I've proposed in this mail requires a big change,
so... not sure if it's feasible right now.





-- 
Iñaki Baz Castillo
<ibc at aliax.net>