[Linux-cluster] Linux Virtual Server Vs RedHat Cluster

[Fajar A. Nugraha]

Manilal K M wrote:

>Yesterday I came across Linux Virtual Server. I have read the
>documents at  http://www.redhat.com/docs/manuals/csgfs/browse/rh-cs-en/pt-lvs.html.
>Now I'm confused more ..
>  
>
Think of Linux Virtual Server (LVS) as a load balancer. You have one (or 
more) machine functions as load balancer that distributes the load to 
multiple "real" servers. Usually you need some kind of frontend to LVS, 
such as piranha or keepalived.

Each one of this "real" server needs to know how to handle the requests 
in the same way. Usually this means each real server needs to have 
identical data, either synchronized at application level (the way MySQL 
cluster does),  manually synchronized (e.g. with rsync), or shared data 
(via NFS or cluster file system). The GFS-part of redhat cluster can be 
used to provide cluster file system for your real servers, but you 
should also make sure that your application can operate on shared data 
without causing corruption.  For example, you can have multiple servers 
running apache accessing the same data/files provided by gfs and it 
should work OK, but you should not have multiple MySQL server accessing 
the same files.

Since your priority is HA (which means active-standby configuration is 
OK), you can simply use redhat cluster without GFS. The cluster suite 
can provide mechanism for checking your services, and restarting or 
relocating the service if it fails. This means that if you have only one 
service, it will only run one node, leaving the other node idle. But if 
you have multiple services (apache, MySQL, etc) you can distribute the 
services on both nodes, and if one node fails the other node can take 
over the services.

If you need HP and HA you can use redhat cluster with GFS to provide 
cluster file system and run your services on both nodes, but you'll also 
need some kind of load balancer (such as LVS) to distribute the load 
between those two nodes.

-- 
Fajar