Derek Martin wrote:
It really depends, but mostly it isn't. One of my earliest gigs was managing just such an environment, which mostly included a few custom applications which were not designed to be clustered. With the right hardware, it's fairly trivial. But the right hardware is expensive.
Clustering non-HA apps can be trivial if those apps have few dependencies. For example, clustering Apache by itself is easy. You just need a storage resource, a network resource, and the startup and shutdown scripts.
The complexity arises when service groups depend on other service groups. In a three-tier web app you have the web server, the application server and the database server. There are dependency chains that have to kept intact for the whole thing to work. Service migration needs to be planned so that you don't end up with all three service groups running on a single node. That's just one point in a simple three-node cluster. Consider expanding that to a half-dozen nodes with several dozen service groups with various dependencies to each other. Planning that out is a lot of work and there are few short cuts to be had.
"The right hardware"? That just costs money. It's one of the few cases where throwing money at a problem actually is part of the solution.
-- Rich P. _______________________________________________ Discuss mailing list Discuss@blu.org http://lists.blu.org/mailman/listinfo/discuss
