Specifications

Chapter 6: Administering Virtual Clusters
78 Equalizer Installation and Administration Guide
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 Static Weight” on page 90.
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.
Providing FTP Services on a Virtual Cluster
Virtual clusters that provide service on the FTP control port (port 21) must be layer 4 and have
special requirements:
• FTP clusters occupy two virtual cluster slots, even though only one appears. This permits
Equalizers NAT subsystem to rewrite server-originated FTP data connections as they
“gateway” to the external network.
• FTP data connections always have a sticky time of one second. This is necessary to support
the passive mode FTP data connection that most web browsers use.
• FTP virtual clusters do not support port redirection.
For more information about supporting passive mode FTP data connections, refer to “Enabling
Passive FTP Connections” on page 53.
Configuring a Cluster to Use Server Agents
A server agent collects performance statistics from a server. If you configure a cluster to use server
agents, Equalizer periodically contacts the server agent daemon running on each server and
downloads the server performance statistics. You can also customize server agents to report on
server resource availability; then Equalizer can stop sending requests to a server if a database or
other vital resource is unavailable.
To configure a cluster to use server agents (see Figure 40), follow these steps:
1. Log into the Equalizer Administration Interface in edit mode.
2. In the left frame, click the name of the cluster to be configured. The cluster’s parameters appear
in the right frame.
3. Select Change Cluster Parameters from the local menu. The modify cluster screen opens in
the right frame.
4. Check the server agent checkbox.
Note – When you configure a cluster to use server agents, each server in the cluster must run a
server agent daemon, so that the agent can provide status information to the Equalizer. If no
agent is running on a server in a cluster configured to use the server agent load balancing policy,
then the Equalizer will load balance without using the agent return value for that server (unless
pedantic agent is set for the cluster, in which case Equalizer regards that server as down).