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> I have some doubts about LVS:
>
> 1) Can LVS do any load balancing job on database server/application?
> For example, someone install a database server on the director and the
> real servers accesing the database on director. Is there any load
> balancing?
I am not sure what you are asking here. The database runs on the
director? That would be unusual, but possible. Whatever the real
servers were doing could be load balanced, but the accesses to
the database on the director would not be.
In general, a database is hard to load balance because of the
distributed storage problem. It is hard to do distributed
disk storage, and make sure that an update on one system
is seen immediately by another system. Intermezzo, GFS and
others are attempts to solve this problem.
> 2) Let say we got a director and a backup for the director and several
> real servers. As I know that when the director is active, the backup is
> inactive. Is there any way that both are active so that the backup is
> not doing nothing but just listening to the heartbeat of the active
> director?
Use two virtual IPs, and make use of the very course DNS load balancing
( a very simple round robin effect). In normal practice, each director
would have one of the two VIPs, and DNS would direct some of the load
to one and some of the load to another. If one director fails, then
the other director would have both VIPs and thus respond to all requests.
It is possible for one hostname to have multiple addresses:
# nslookup www.weather.com
Server: panic.ohr.gatech.edu
Address: 130.207.47.194
Non-authoritative answer:
Name: www.weather.com
Addresses: 64.68.71.140, 216.35.172.135
Note that if you have two servers, and two services, you can set up
an HA cluster with one service running on one server, and the other
service running on the second server. In a failover situation, you
have both services running off a single server. This may result
in degraded performance, but it might be better than no service
at all during a system failure of some kind.
> 3) Can somebody tells me where to look for success story about lvs or
> clustering solutions?
Somebody else will have to fill this in. However, I have no doubts
that for sites with static content (ie the content is the same on
all servers - this can include CGI and PHP - use persistance if
necessary), that LVS can be used to set up a very capable web farm.
However, to get real performance out of it, you need serious network
bandwidth. People who can afford that kind of bandwidth can usually
afford to use Foundry Server Iron switches or something for load
balancing (which is what www.weather.com does).
If you have a computationally intensive task for the servers to
do (ie SSL encryption, compute intensive CGI etc) then LVS can
make sense for lower bandwidth uses too.
--
John Cronin
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