Re: Active/Active servers

["Taymour A. El Erian" <taymour.elerian@tedata.net>]

Clowser, Jeff (Contractor) wrote:
> > Howard Chu wrote:
> >     
> > > Aaron Richton wrote:
> > > Multimaster support is present in OpenLDAP 2.4.
> > >       
> > That's not quite the complete answer though. He's also talking about
> >     
> two 
>   
> > servers sharing the same storage. In general, that is not supported in 
> > BerkeleyDB and is certainly not supported by back-bdb or back-hdb.
> >     
>
> What are you trying to accomplish?  
>   
Add high availability to my master servers, avoiding replication.
> If you want high availability for ldap writes, create two master servers
> (each with their own storage/db files) in multimaster mode (2.4) or
> mirror mode, and set up the load balancer such that all connections to
> the VIP go to one master, failing over to the second master if the first
> one is down. 
What happens when that one master comes back again ?, will the previous 
master replicate the data to it, what about conflicts ?
>  (Active/Hot standby)  This provides better reliability
> because there are no single points of failure (i.e. a disk failure/San
> issue or db corruption on one won't generally affect the other, so you
> can fail over from these kinds of problems), and minimizes write
> conflicts (since only one master is being written to at any given time).
> Additionally, create a bunch of read-only replicas behind a separate
> load balanced VIP for the majority of your traffic (most ldap clients
> are generally just doing auth and/or lookups so, are read only).
>   
I need the master/replica to be transparent to the clients, so I should 
use chaining ?

Master 1   Master2         Replica1   Replica2   (Chain)
   |_________|                     |________|  
            | VIP1                              |
            |____________________|
                                 | VIP2

Now, I use VIP2 on the clients and VIP1 in the chain configuration ?
> If you are trying to do this to scale up write performance, multiple
> masters (in any form) is not really the answer (check the archives for
> the many times this has been discussed).  Basically, it comes down to
> multiple masters still have to write the same data to every master, so
> this doesn't increase performance.  Even with them sharing the db files,
> the disk I/O is probably the bottleneck on performance, so this wouldn't
> really help.  In general, your percentage of writes to reads in LDAP
> should be very small, so having the read-only replica cluster (which can
> be expanded out to, for all practical purposes, an unlimited number of
> servers) will take most of the traffic off your masters, which are
> limited in scalability (under this model) to as big a box as you can
> build for one server (but this should be fine if you offload most of the
> clients to the R/O cluster, and just have writes go to the masters).
>
>
>   
> > > On Thu, 6 Dec 2007, Taymour A. El Erian wrote:
> > >
> > >       
> > > > Hi,
> > > >
> > > >   I am not sure if this is the right place to ask this or not. If I
> > > >         
> install
>   
> > > > 2 nodes of OpenLDAP and they both share the same SAN storage, is it
> > > >         
> possible
>   
> > > > that both of them would be working active/active ?, i.e. behind a
> > > >         
> load
>   
> > > > balancer (doing reads and writes).
> > > >         
>
>   


--
Taymour A El Erian
System Division Manager
RHCE, LPIC, CCNA, MCSE, CNA
TE Data
E-mail: taymour.elerian@tedata.net
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Tel:    +(202)-33320700
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