[Serusers] Global Failover Server

Greger V. Teigre greger at teigre.com
Fri Jul 7 11:48:48 CEST 2006

Yes, but this depends on your deployment setup and policies. Obviously, 
you cannot support all features with all UAs. Three-way conferencing for 
example. There's no guarantee that REFER and NOTIFYs work for three 
random UAs from different vendors. There are still too many bugs around. 
So, you need to say: If you have this and that UA, you will probably not 
get three-way conferencing.  Not much difference from saying: If you 
have this and that UA, you may experience service outages.

There are several ways of creating server-side redundancy and 
scalability. Unfortunately, none are trivial. There are three I have 
heard have been successfully used in large-scale setups:
1. Cacheless usrloc with a mysql cluster as back-end DB combined with 
implementation of the Path header (to find the registrar of a given UA). 
No replication across servers
2.  Multiple SER registrars, each with a standalone, local DB and where 
SIP is used to replicate registrations.  By storing replications from a 
peer in a location_peer1 table and then lookup using this table, you can 
route INVITEs to the registrar being able to pinhole the NAT in front of 
a given UA
3. Each SER is connected to a single mysql DB cluster as in #1, but 
since usrloc also is in memory (cacheless usrloc is not used), 
replication is done between the SER servers and save_memory() is used to 
store the location only in memory (the registrar updates the cluster 
with save())

Each of these three can be combined with either:
a. call-id sticky front-end load balancer (commercial or modified LVS)
c. Linux HA creating two and two peers

Only b) combined with either 1) or 3) or 2+c) can give geographic, 
client and server-side redundancy and scalability.

Scalability and redundancy is sort of a pet project of mine... I would 
like to see a simple, clear-documented and code-supported setup that 
satisfies most common requirements. Currently I'm leaning against #2 
(which actually can be implemented in vanilla SER 0.9.x, but would be 
easier and better with built-in support). I'm thinking about a setup 
where two and two servers are peers to eachother using Linux HA. Both 
servers would have one active SER instance and one inactive ready for 
taking over for the peer.

I have posted this overview to:

See also:

G.Jacobsen wrote:
> Samuel,
> Do you happen to know what percentage of UAs out there are really 
> "Compliant" UAs ?
> My impression so far regarding SRV DNS records is that they are 
> theoretically a nice feature but unfortunately almost useless since 
> one needs to cater for those non-compliant UAs anyway. I would love to 
> be convinced of the contrary.
> Can anyone supply real usage figures regarding compliant/non-compliant 
> UAS ?
> Gerry
>     -----Original Message-----
>     *From:* serusers-bounces at lists.iptel.org
>     [mailto:serusers-bounces at lists.iptel.org]*On Behalf Of *samuel
>     *Sent:* Donnerstag, 6. Juli 2006 14:52
>     *To:* Ritesh Jalan
>     *Cc:* seruser List
>     *Subject:* [Bulk] Re: [Serusers] Global Failover Server
>     Look at RFC 3623.
>     Cofigure two SRV entries in
>     your DNS, one pointing to the UAS SERver and another to the UK server.
>     "Compliant" UAs will try to contact the other proxy upon failure
>     of their current one.
>     Samuel.
>     2006/7/5, Ritesh Jalan <ritesh.j at net4.in <mailto:ritesh.j at net4.in>>:
>         Hi All
>         Pls. guide me how can we implement failover on SIP Server
>         located globally, Like one server in USA another in UK.
>         Ritesh Jalan
>         Mobile: 91-9818616329
>         MSN: ritesh_jalan at hotmail.com <mailto:ritesh_jalan at hotmail.com>
>         _______________________________________________
>         Serusers mailing list
>         Serusers at lists.iptel.org <mailto:Serusers at lists.iptel.org>
>         http://lists.iptel.org/mailman/listinfo/serusers
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