Specifications

Chapter 6: Administering Virtual Clusters
80 Equalizer Installation and Administration Guide
Enabling Persistent Sessions
Equalizer provides several methods by which sessions 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 sessions are enabled using the sticky time cluster parameter and
(optionally) the inter-cluster sticky cluster flag. See “Enabling Sticky Connections” on page 80.
For Layer 7 clusters, persistent sessions are enabled using the persist or the once only cluster flags
(which can be enabled together or separately). See “Enabling Cookies for Persistent Sessions” on
page 81 and “Enabling the Once Only Flag for Persistent Connections” on page 82.
Enabling Sticky Connections
For L4 TCP and L4 UDP clusters, which only support L4 load balancing, 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.
When you enable sticky connections, the memory and CPU overhead for a connection increase.
This overhead increases as the sticky period increases. 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.
When you enable inter-cluster stickiness, you can ensure that Equalizer directs requests from a
particular client to the same server even if the connection is to a different virtual cluster. Inter-
cluster stickiness only works for L4 clusters. Although L7 clusters automatically provide inter-
cluster stickiness, inter-cluster stickiness will not work between L4 and L7 clusters.
You must enable inter-cluster stickiness for all the clusters to be bound together. The clusters with
enabled inter-cluster stickiness should contain identical sets of server IP addresses. For example:
Cluster www.coyotepoint.com:http
Server srv1@192.168.0.5
Server srv2
Cluster www.coyotepoint.com:https
Server srv1@192.168.0.5
Server srv2
To enable sticky connections (see Figure 41), 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.