Coyote Point Systems Equalizer Spezifikationen PDF herunterladen (Seite 232)

Server Pools and Server Instances

l Weight Spread Coefficient regulates the speed of change to a server’s dynamic weight. The weight

spread coefficient causes dynamic weight changes to happen more slowly as the difference between the

dynamic weight and the initial weight increases.

l Optimization Threshold controls how frequently Equalizer adjusts dynamic weights. If Equalizer adjusts

server weights too aggressively, oscillations in server weights can occur and cluster-wide performance can

suffer. On the other hand, if Equalizer does not adjust weights often enough, server overloads might not be

compensated for quickly enough and cluster-wide performance can suffer.

Aggressive Load Balancing

After you fine-tune the initial weights of each server in the cluster, you might discover that Equalizer is not

adjusting the dynamic weights of the servers at all: the dynamic weights are very stable, even under a heavy load.

In this case, you might want to set the cluster’s load balancing response parameter to

fast

. Then Equalizer tries to

optimize the performance of your servers more aggressively; this should improve the overall cluster performance.

For more information about setting server weights, see "Adjusting a Server’s Initial Weight" on page 253.

Dynamic Weight Oscillations

If you notice a particular server’s dynamic weight oscillates (for example, the dynamic weight varies from far below

100 to far above 100 and back again), you might benefit by choosing

slow

response for the cluster. You should also

investigate the reason for this behavior; it is possible that the server application is behaving erratically.

Using Active Content Verification (ACV)

Active Content Verification (ACV) is a mechanism for checking the validity of a server. When you enable ACV for

a server pool, Equalizer requests data from each server in the server pool and verifies that the returned data

contains a character string that indicates that the data is valid. You can use ACV with most network services that

support a text-based request/response protocol, such as HTTP. Note, however, that you cannot use ACV with

Layer 4 UDP clusters.

ACV checking is performed as part of the high-level TCP probes that Equalizer sends to every server by default.

To enable ACV, you specify an ACV response string for a server pool. Equalizer which will then search for the ACV

response string in the first 1024 characters of the server’s response to the high-level TCP probes. If the ACV

response string is not found, the server is marked down. An ACV probe can be specified if the service running on

the server’s probe port requires input in order to respond.

How ACV works is best explained using a simple example. The HTTP protocol enables you to establish a

connection to a server, request a file, and read the result.

> telnet www.myserver.com 80 >>>>

User requests connection to server.

Connected to www.myserver.com >>>>

Telnet indicates connection is established.

> GET /index.html >>>>

User sends request for HTML page.

Server responds with requested page.

<TITLE>Welcome to our Home Page </TITLE>

</HTML>

Connection closed by foreign host >>>>

Telnet indicates server connection closed.

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