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Load balancing


ruperthair
18-06-2009, 22:56
Quote Originally Posted by gigabit
After the load balancing node forwards the requests to the webserver, does the data then go back through the load balancing node or just directly back to the client?
It can't go directly back to the client as the TCP connection was made from the client's IP to the load balancer's IP. The client (or their NAT router) wouldn't accept packets from some random web server's IP.

Load balancers use NAT (specifically DNAT) to change the destination IP address of incoming packets to the IP of one of your web servers. The web servers are usually 'behind' the load balancer (i.e. on a private network routed to though the load balancer) but I don't think that's possible on OVH's standard servers.

You set up the load balancer to stick the traffic to the web servers out on the same interface where it came in, but this halves your bandwidth. I've not looked at the prices for OVH's load balancers, but unless they are far too expensive, I that they are the best way to go.


Quote Originally Posted by gigabit
Obviously if it goes back through the load balancer its a bit counter productive if youre trying to balance some gigabit servers through a 100mbit node :P
You'll tend to find that, unless your web servers are serving out static content (and then why do you need a load balancer in the first place), you won't saturate 1gbit with a single server. If you are going to run your own load balancer, I would suggest that you give it a gigabit but only give the web servers 100mbit.

In case you've not thought about this option: You can do some load balancing with nothing more than standard DNS. Details here:

http://www.google.co.uk/search?q=dns+load+balancing

Ashley
18-06-2009, 22:19
The load balancer is probably a router/switch. Your information has to go through it anyway.

What I want to know is persistent sessions!

gigabit
18-06-2009, 22:10
I've been learning about load balancing lately (using software on linux rather than OVHs load balancing method) and ive got a question that hasnt really been mentioned anywhere:

After the load balancing node forwards the requests to the webserver, does the data then go back through the load balancing node or just directly back to the client? Obviously if it goes back through the load balancer its a bit counter productive if youre trying to balance some gigabit servers through a 100mbit node :P

Thanks