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).

F5- Node Ratio All 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;

F5- Node Ratio Uneven

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.

F5 Change Pool Load Balance

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.

F5 Change Pool Ratio Testing

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;

F5- Pool Member Ratio Uneven

Open the Pool > Select the Node from here.

F5- Change Pool Member Ratio

Change there ratio here > Update.

F5- Change Pool Member Ratio

Now change the Load Balancing Method to Node (member) > Update  >Note: Here, ratios are shown on the Pool page.

F5- Change Pool Balance Ratio

Reset your counters, and wait a while, you will see the other server is now getting most of the traffic.

F5- Change Pool Balance Ratio

In large production environments, you will probably want to use Dynamic Load Balancing methods, so I’ll look at those next.

Related Articles, References, Credits, or External Links

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Author: PeteLong

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