Specifications

Chapter 6: Administering Virtual Clusters
92 Equalizer Installation and Administration Guide
4. Enter the new weight in the weight field.
5. Click the commit button.
Setting Static Weights for Homogenous Clusters
If all the servers in a cluster have the same hardware and software configurations, you should set
their static weights to the same value initially. We recommend that you use a static 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
static weights accordingly and again monitor their performance. You should adjust server weights
by small increments; for example, you might set the static 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%.
Setting Static Weights for Mixed Clusters
Equalizer enables you to build heterogeneous clusters using servers of widely varying capabilities.
Adjust for the differences by assigning static weights that correspond to the relative capabilities of
the available servers. This enables you to get the most out of your existing hardware, so you can use
an older server side-by-side with a new one.
After you assign relative static weights, monitor cluster performance for two to three hours under
load. You will probably fine-tune the weights and optimize performance of your cluster two or three
times.
Continue monitoring the performance of your cluster and servers and watch for any trends. For
example, if you notice that Equalizer always adjusts the dynamic weights so that the weight of one
server is far below 100 and the weight of another is far above 100, the server whose dynamic weight
is consistently being reduced might have a problem.
Shutting Down a Server Gracefully
To avoid interrupting user sessions, make sure that a server to be shut down or deleted from a
cluster no longer has any active connections. When a server’s static weight is zero, Equalizer will
not send new requests to that server. Connections that are already established continue to exist until
the client and server application end them or they time out because they are idle.
To shut down servers in a generic TCP or UDP (L4) cluster, you can set the server’s weight to zero
and wait for the existing connections to terminate. However, you need to quiesce servers in HTTP
and HTTPS (L7) clusters to enable servers to finish processing requests for clients that have a
persistent session with the server.
When you quiesce a server, Equalizer does not route new connections from new clients to the
server, but will still send requests from clients with a persistent session to the quiescing server. Once
all the persistent sessions on the server have expired, you can set the server’s static weight to zero;
then Equalizer will not send additional requests to the server.
Note – Equalizer’s ALB algorithm can take 10-15 minutes to fine-tune cluster performance when
you change static weights. After you change static weights, wait 30 minutes before you judge the
cluster’s ALB performance.