North American Network Operators Group

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Re: load balancing and fault tolerance without load balancer

  • From: Mark Smith
  • Date: Fri Mar 14 18:47:27 2008

On Sat, 15 Mar 2008 00:42:26 +0800 (CST)
Joe Shen <[email protected]> wrote:

> hi,
>    we plan to set up a web site with two web servers.
>    The two servers should be under the same domain
> name.  Normally,  web surfing load should be
> distributed between the servers. when one server
> fails, the other server should take all of load
> automatically. When fault sever recovers, load
> balancing should be achived automatically.There is no
> buget for load balancer.
>    we plan to use DNS to balance load between the two
> servers. But, it seems DNS based solution could not
> direct all load to one server automatically when the
> other is down.
>    Is there any way to solve problem above? 

One option might be to run two instances of VRRP/CARP across the hosts.
You have Host A being the primary/master for one IP address that's in
your DNS, and Host B being the primary/master for the other IP addess
that's in your DNS. Host A is the secondary/backup for the IP address
normally owned by Host B and Host B is the secondary/backup for the IP
address normally owned by Host A. When, for example, Host A fails, Host
B takes over being the primary/master for both IP addresses in your
DNS, giving you your continued availability. If you want make that fail
over transparent to load, you'd need to keep the load on the hosts <50%
under normal, non-fail circumstances.



        "Sheep are slow and tasty, and therefore must remain constantly
                                   - Bruce Schneier, "Beyond Fear"