Alan McKay wrote:

My main areas of interest are :

• DB clustering (PostgreSQL) - yeah, we're looking at commercial stuff

and skytools

No DB clustering here, though if I had to pick I'd probably go for Oracle RAC. MySQL clustering doesn't seem good, Postgres sounds interesting, their EnterpriseDB grid stuff perhaps, haven't looked too much into it.

• web server clustering - Apache on CentOS

The web servers I manage serve about 2 billion requests a day on CentOS 5.2, no clustering, we use load balancing with commercial load balancers, currently F5 LTM, though will be evaulating Citrix Netscaler soon. The servers run java/tomcat from original sources, so despite having an older version of the OS there really isn't much security risk. Any network-based attacks are thwarted by the load balancers (such as the recent Apache slow DOS attack).

F5 runs all of their gear on CentOS as well, at least everything that runs TMOS (which covers GTM, LTM, and a few others as well I think). It is a stripped down version.

Don't let that make you think you can grab their software and install it on your own server though, their licensing will prevent that from happening.

• storage clustering

Using commercial solutions here too, our NFS cluster from Exanet does run on top of CentOS 4.4, though they use their own hardware (IBM X3650) to make it as supportable/stable as possible. These are NAS head units only they rely on another storage system in the back end for the raw disk space to serve to clients.

At my previous company I was planning on implementing a GFS cluster on top of RHEL and VMware with a fiber channel/ raw device map back end for NFS. Though didn't have time or budget to do it before I left. Such a solution for my current company would be torn to shreds as it doesn't scale nearly as well.

Our back end storage from 3PAR runs on top of Debian, you'd never know it was Debian unless you telnetted to it on port 22 to see the Debian SSH banner(I like to poke around).

Clustering is a really complex thing to get right, it can often cause more problems than it would otherwise prevent. Even some high end clustering is really poor. A couple of jobs ago I had to use BEA Weblogic application clustering for a massive J2EE app. Ran us roughly $10 or was it $20k per CPU. We had major, major outages with that thing. Most of the time we(and BEA) were able to trace it to the weblogic cluster itself.

So think long and hard about what your trying to accomplish, and if there is another way to get there without relying on clustering. When I say clustering I mean pretty tight integration between the systems in the cluster, where if one box can go whacky it can take the rest of the cluster with it.

nate