Re: Setting up a Redundant Webserver setup

To: ben@xxxxxxxxxxxxx
Subject: Re: Setting up a Redundant Webserver setup
Cc: lvs-users@xxxxxxxxxxxxxxxxxxxxxx
From: "Lorn Kay" <lorn_kay@xxxxxxxxxxx>
Date: Fri, 24 Nov 2000 06:46:43 -0000
I was wondering if anyone had any suggestions as to the best way to setup a
redundant (no single point of failure) Load-balanced webserver environment
using LVS.

I was thinking something like this

2 LVS systems (for redundancy)

6 - 20 Webservers, pretty much the same specs

This is possible with two Directors each running heartbeat. Only one is the live Director and the other becomes the Director when heartbeat detects the failure of the primary Director. What you call "Webservers" LVS calls "Real Servers" within the LVS.

Read the HOWTO for more details.

(Failure of the Real Servers is reported to the Director(s) with the PERL program "mon").

2 File servers  (NFS) with replication
(Is this possible, I've looking into a lot of solutions, but I was wondering
if anyone has any experience with this)

This is not so easy. There is currently no way (that I know of) to establish file locking and local I/O on more than one machine with any software-based system. DRDB, GFS, and other efforts are under development. But using NFS will only allow you to have NFS server--everything else is an NFS client (still with Read/Write access but the single NFS server is a single point of failure unless
you use a hardware solution like a SAN/RAID).

(Is it possible to load balance Mysql, reading over NFS, or would I be in
better shape trying to setup two seperate DB servers with some sort of

rsync or a simple cron job running cpio on an NFS mount could replicate the data
between Real Servers, but then you have two "master" copies of the data !?!

This, of course, will lead to database synchronization problems. (Who has the "real" master
copy of the data?)

If I can't get the replication working, I may just buy a Sparc, and pray
that they are as stable as they are expensive.

Sun has (expensive) cluster solutions to prevent a single point of failure. I'm not sure of the very latest, but you'll probably be talking about an underlying SAN/RAID solution
to solve the data synchronization problem.

(Advantages of the file servers is that It makes the Webservers a lot
cheaper (no need for RAIDs, or Big drives)

Linux supports software RAID by the way. So you could use RAID to help protect
yourself from a drive failure at least.

Also I was wondering if there were any plans for a CPU LOAD based
implementation of the LVS software, using daemons on the webservers, or if
you can change the weights (for the weighted round robin) in real-time, so
that we could write our own Pseudo CPU load balancing system..

LVS can do this now. See weighted round robing scheduling method in the HOWTO.

Take a look at

for a list of commercial versions of LVS, or perhaps you want
to look at Ultra Monkey.


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