[Serusers] ser mysql/cache sync

[Andrei Pelinescu-Onciul]

On Jul 10, 2005 at 10:49, Greger V. Teigre <greger at teigre.com> wrote:
> Jack Wei wrote:
> >i am running a cluster with 2 sers.  i start the 1st ser and several
> >users registers.  the users show up in both the cache and the mysql
> >db.  then i start the 2nd ser, and it loads the db into the cache.
> >when the cache entries in the 2nd server times out, the entries are
> >deleted from the db.  however, when the users registers in the 1st
> >ser, they aren't entered into the db.  how do i fix this problem?
> >
> >the db_mode is set to "2" w/ timer_interval at "10".  i've even tried
> >setting the db_mode to "1", but that didn't help.
> 
> Write-through DB mode will write all usrloc changes to the DB. However, all 
> locations are cached in ser memory. This means that there is no way a 
> secondary ser can reload a location from DB. If a location is not found in 
> memory, it is assumed not there.  A new caching approach has been discussed 
> previously on this list (or was it serdev?).
> 
> You can do the following:
> - Use write-through DB mode to the shared SQL DB
> - Use t_replicate to the secondary ser
> - On the secondary ser, call save_memory() instead of save() (as the 
> location has already been saved in DB)
> 
> This only works for deployment scenarios where EUCs are not NATed.  The 
> reason is that the secondary ser will have another public IP address than 
> the primary and restricted NATs will not accept incoming packets from other 
> IPs than the one the EUC has registered to.
> 
> The way to solve this is to either route all INVITEs coming to the 
> secondary through the primary (ex. using Path) or to set up LVS (or 
> similar) where both SERs have the same IP address.  However, currently LVS 
> does not do Call-id based load balancing and people who report this 
> scenario have patched LVS or use a commercial load balancing solution.

It depends a lot on what you are trying to solve: failover or load
balancing. For failover you need the same ip configured on all the
machines, t_replicate and a way (outside of ser) of cutting down the
traffic from the slave machines (and allowing only the primary).
I think openbsd/freebsd carp would work perfectly for such a setup (I
haven't tried it though).

For load balancing it depends a lot on your setup. For example load
balancing over call-id makes sense only if you share the entire
database. OTOH database access and database writes in particular are the
things which will slow ser the most, so it's better to keep at least separate
usrloc dbs. In this case, you would need balancing after r-uri for
requests and to-uri for registers.
You could use  a ser + dispatcher as a load balancer in front. You don't
even need Path support if you use only one load balancer (you just
forward everything back through it).



Andrei