Coyote Point Systems Equalizer Spezifikationen PDF herunterladen (Seite 253)

Adjusting a Server’s Initial Weight

Equalizer uses a server’s initial weight as the starting point for determining the percentage of requests to route to

that server. As Equalizer gathers information about the actual performance of a server against client requests, it

adjusts the server’s current weight so that servers that are performing well receive a higher percentage of the

cluster load than servers that are performing at a slower rate.

When you install servers, set each server's initial weight value in proportion to its “horsepower.” All the initial

weights in a cluster do not need to add up to any particular number;

it’s the ratio of the assigned server weight for a

server to the total of all the server weights that determines the amount of traffic sent to a server

For example, you might assign a server with 4 dual-core 64-bit processors operating at 3.40GHz a value of 100 and

a server with 2 dual-core 64-bit processors operating at 1.86GHz a value of 50. The first server will initially receive

approximately 66% (100 divided by 150) of the traffic. The second server will initially get about 33% (50 divided by

150) of the traffic. It’s important to note that setting the initial weights of these servers to 100 and 50 is equivalent

to setting the initial weights to 180 and 90.

Values for server weights can be in the range 0-200, with 0 meaning that no new requests will be routed to the

server, essentially disabling the server for subsequent requests. In general, you should use higher initial weights.

When the load balancing policy is

not

set to round robin or static weight, using higher initial weights will produce

finer-grained load balancing. Higher weights enable Equalizer to adjust server weights more gradually; increasing

the weight by 1 produces a smaller change if the starting weight is 100 than it does if the starting weight is 50.

However you set the initial weights, Equalizer will adjust the weight of servers dynamically as traffic goes through

the cluster. Dynamic server weights might vary from 50-150% of the statically assigned values. To optimize

cluster performance, you might need to adjust the initial weights of the server instance in a server pool based on

their performance.

Note - Equalizer stops dynamically adjusting server weights if the load on the cluster drops below a certain

threshold. For example, if web traffic slows significantly at 4:00 AM PST, Equalizer will not modify server weights until

traffic increases again. Because a server’s performance characteristics can be very different under low and high

loads, Equalizer optimizes only for the high-load case. Keep this in mind when you configure new Equalizer

installations; to test Equalizer’s ALB performance, you’ll need to simulate expected loads.

Setting Initial Weights for Homogenous Clusters

If all the servers in a cluster have the same hardware and software configurations, you should set their initial

weights to the same value initially. We recommend that you use a initial weight of 100 and set the load-balancing

response parameter to

medium

As with any new configuration, you will need to monitor the performance of the servers under load for two to three

hours. If you observe that the servers differ in the load they can handle, adjust their initial weights accordingly and

again monitor their performance. You should adjust server weights by small increments; for example, you might

set the initial weight of one server to 110 and the other to 90. Fine-tuning server weights to match each server’s

actual capability can easily improve your cluster’s response time by 5 to 10%.

Note - A change to a server’s initial weight is reflected in cluster performance only after Equalizer has load balanced

a significant number of new client requests for up to 30 minutes against the cluster in which the servers reside. When

testing initial weights, it is most useful to use a load-generating tool to run typical client requests against the cluster to

determine appropriate server initial weights.

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Equalizer Administration Guide

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