[Linux-cluster] Load balancing clustered services

[Jeff Sturm]

Greetings,
 
The Red Hat Cluster Suite page says the following:


 "For applications that require maximum uptime, a Red Hat Enterprise
Linux cluster with Red Hat Cluster Suite is the answer. Specifically
designed for Red Hat Enterprise Linux, Red Hat Cluster Suite provides
two distinct types of clustering:

    * Application/Service Failover - Create n-node server clusters for
failover of key applications and services
    * IP Load Balancing - Load balance incoming IP network requests
across a farm of servers"


The implication seems to be that the first type addresses high
availability, and the second scalability.  What is the optimal way to
get both?

Please understand that I am already a user of GFS and LVS.  I'm asking
the question because the two seemingly have nothing in common.  For
example, cman knows about cluster membership and can immediately react
when a node leaves the cluster or is fenced.  On the other hand, LVS
(together with either piranha or ldirectord) keeps a list of real
servers, periodically checking each and removing any found to be
unresponsive.

It seems like there are a couple drawbacks to this bifurcated design:

- once cman realizes a node has left the cluster, there is a delay
before ipvs updates its configuration, during which user requests can be
routed to a dead server
- two distinct sets of cluster configurations have to be maintained

Am I misunderstanding something fundamental, or is that the way it is?


-Jeff