Coyote Point Systems E350GX, Руководство по установке и администрированию

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Configuring a Cluster’s Load-Balancing Options
Equalizer Installation and Administration Guide 129
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.
1. Log into the Administrative Interface using a login that has
add/del
access for the cluster (see “Logging In” on
page 52).
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 the
Probes
tab in the right frame.
4. Check the
server agent
checkbox.
5. In the
server agent port
field, specify the port used to contact the server agent; the default port is 1510.
6. If your agent needs to have a string sent to it before it will respond, provide the string to be sent to the agent in
the
agent probe
field.
7. Click the
commit
button.
For information about writing your own server agents and using agents to monitor server resource availability, see
“Server Agent Probes” on page 255.
Enabling Persistent Server Connections
Equalizer provides several methods by which connections between clients and servers can be made persistent ; that
is, it is possible to route a series of requests from a particular client to the same server, rather than have the Equalizer
load balance each request in the series -- potentially sending each request to a different server.
For Layer 4 clusters, persistent server connections are enabled using the
sticky time
cluster parameter and
(optionally) the
inter-cluster sticky
cluster flag. See “Enabling Sticky Connections” on page 129.
For Layer 7 clusters, persistent server connections are enabled using the
persist
and
always
cluster flags. See
“Enabling Cookies for Persistent Connections” on page 130.
Enabling Sticky Connections
For Layer 4 TCP and UDP clusters, you can use IP-address based sticky connections to maintain persistent sessions.
The
sticky time
period is the length of time over which Equalizer ensures that it directs new connections from a
particular client to the same server. The timer for the sticky time period begins to expire as soon as there are no
active connections between the client and the cluster. If Equalizer establishes a new connection to the cluster,
Equalizer resets the timer for the sticky time period.
Sticky connections are managed on Equalizer using sticky records that record the IP address, port and other
information for the client-server connection. When you enable sticky connections, the memory and CPU overhead
for a connection increase. This overhead increases as the sticky time period increases.
Consequently, you should use the shortest reasonable period for your application and avoid enabling sticky
connections for applications unless they need it. For most clusters, a reasonable value for the sticky time period is
600 seconds (that is,10 minutes). If your site is extremely busy, consider using a shorter sticky time period.
[Also see the description of the
sticky netmask
global parameter in the section “Global Networking Parameters” on
page 87.]
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
require agent response is set for the cluster, in which case
Equalizer regards that server as down).