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).