[Linux-HA] High Availibility and LoadBalancing
ranaldo at unina.it
Thu Mar 10 04:38:24 MST 2005
Let's suppose i have an heavy loaded "A" service (for example incoming mail
with antivirus/antispam) and i want to load balance it over 4 servers.
A simple configuration is 1 frontend (linux virtual server) and 4 backend
all of them running "A" and storing locally the data (in the examples the
own mail queue).
Now Let's suppose i want to implement High Availibility over them.
The first thing to do is to cluster the frontend over an active/passive
The second is to cluster the 4 backend with other active/passive heartbeat
cluster and sharing data (the mail queue) over a SAN or with DRBD.
In this case i waste 4 slave server.
The best for me *would be* to have a multinode cluster with 4 active
servers: if one of them fails, one of the remaining takes it's services and
But I suppose running two istance of the same service "A", on the same
server could be an heavy configuration problem (if you do not have other
simpler and transparent solutions :), and i do not want to risk with
extermely customized config file (in the example, i cannot have 2 sendmail
binding the same port, of course i can instruct sendmail in order to process
2 queues -the original, and the queue coming from the failed server-, but
it's difficult and dangerous).
So the best for me *is* to have a multinode cluster with 4 active servers
and 1 slave (or more).
Is it possible to implement the above scenario with heartbeat (pheraps in
the version 2) ?
Can i say to heartbeat to stop the failed service when no more slaves are
available in order to avoid services collisions?
In a multinode cluster configuration i suppose i cannot use cross-over
cables and nullmodem cables.
Wath may i do? Need i use 2 local switch (couse 1 of them could fail!) and
so 3 ethernet cards on every server?
Again, i think i cannot use DRDB to replicate data between more of two
servers. Need i to use only a SAN?
Finally. Is this scenario a good architectural pattern? Are there some
Sorry for English, Best Regards
Federico II University - Naples (IT)
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