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Re: Active/Active servers

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
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:


I am not sure if this is the right place to ask this or not. If I
2 nodes of OpenLDAP and they both share the same SAN storage, is it
that both of them would be working active/active ?, i.e. behind a
balancer (doing reads and writes).

Taymour A El Erian
System Division Manager
TE Data
E-mail: taymour.elerian@tedata.net
Web:     www.tedata.net
Tel:    +(202)-33320700
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Ext:    1101