F5: Static Load Balancing (Ratios)

KB ID 0001700

Problem

In the previous post, we deployed a web load balanced solution with three web servers. Out of the box the BIG-IP solution will use Round Robin load balancing and it will treat all Nodes or Pool Members the same, (it assigns a RATIO OF 1).

Everything gets weighted the same, and the F5 will send requests to the Nodes or Pool members one at a time.

F5- Node Ratio Equal

But what if one of those web servers was a beast of a machine, with much better CPU/RAM than all the others? How do you ensure that gets sent the ‘Lions share’ of the traffic?

Solution

Well you can simply alter the Ratio for that server, you can do that directly on the Node, or you can do it within the Pool on a Pool Member. (That’s why you can see 6 ratios in the examples I’ve posted).

What if I change the Ratios on Nodes AND Pool Members: You can do that, but the load balancing method uses one or the other. So they wont conflict.

So let’s say 10.2.0.11 is a brand new server and has ten times the processing power of the other two nodes like so;

Local Traffic > Nodes > Select the node in question > Change the Ratio accordingly > Update.

F5- Change Node Ratio

Nothing will happen until you change the load balancing method of the Pool. On the properties of the Pool, change the Load Balancing Method to Ratio (node) > Update.

If you reset the counters and wait a while, you can see now that the server is getting (more or less*) 10 times the amount of traffic.

*Note: The maths will never be perfect, and my web pages are all ‘very slightly’ different, which is amplified over time.

Changing F5 Pool Member Ratios

The process is similar, (if you are following along, you might want to change your Node value back to ‘1, not that it will affect anything, it’s just if you are like me you will forget!) So now let’s say we’ve got a new server and its 10.2.0.13, and we want to change the ratio on the Pool Member like so;