Load Balancing

[Piotr Kirklewski]

Hi again

I don't fully understand the concept of load ballancing:

Let say I have three Linux Boxes with Red Hat Enterprise. Should I install MySQL on each of them ? Where is the data stored then?

Cheers

[Don Vanco - Linux Ninja · Accepted solution]

There's a couple layers of "load balancing" possible. Not cracking wise - but have you considered Google? You mention RHEL - consider looking at the on-line manuals for their cluster suite (although arguably it's going to be lacking anecdotal data on the concepts underlying clustering)

You can do "IP load balancing" where you simply have some mechanism to put a series of resources "behind" a single IP (like 5 web servers ALL with the same static content, or DHCP servers that each have a sub-set of leases or some dynamic capability), and then requests for those resources are divided among the physical servers. Depending on the method used to implement IP based load balance there be a minimal amount of intelligence (load assessment) put into it, but not much.

IP load balancing does not offer any kind of "stateful" maintenance of session data, so if a particular server dies all those using resources on the server would lose the session.

See also "Linux HA" "Heartbeat" and "UltraMonkey"


Then there's application load balancing where you again have some series of servers offering up a service or an application, but there's some "secret sauce" that (typically) allows for shared data between them and and (possibly) the ability to maintain session data in the event of a service/server failure (the attached clients do NOT lose their shopping cart contents when the server they are currently talking to locks up, etc).


So - it's hard to answer your question directly because it really comes down to the data that will be on these servers, and how you will script the stop/start/restart action for the application layer when a server or resource fails. Simply throwing up 3 MySQL servers isn't going to do much for you if the intent is that they all support the same "stuff" as you've not provided a mechanism for them to either share data or somehow (individually) access the same data. Buying an "appliance" isn't going to do that for you. Hope that makes sense.....

JMO
Don