Technical data

Connection Errors and Clustering Failover
Administration Guide 13-13
The Dynamic Server List
When you specify a list of WebLogic Servers in the WebLogicCluster parameter, the
plug-in uses that list as a starting point for load balancing among the members of the
cluster. After the first request is routed to one of these servers, a dynamic server list is
returned containing an updated list of servers in the cluster. The updated list adds any
new servers in the cluster and deletes any that are no longer part of the cluster or that
have failed to respond to requests. This list is updated automatically with the HTTP
response when a change in the cluster occurs.
To avoid traffic on a new server you need to test, wait until the newly added server is
fully tested, target it to the cluster and it will become a node of the cluster. This node
will get automatically begin to receive traffic from the proxy.
Failover, Cookies, and HTTP Sessions
When a request contains session information stored in a cookie, in the POST data, or
by URL encoding, the session ID contains a reference to the specific server in which
the session was originally established (called the primary server) and a reference to an
additional server where the original session is replicated (called the secondary server).
A request containing a cookie attempts to connect to the primary server. If that attempt
fails, the request is routed to the secondary server. If both the primary and secondary
servers fail, the session is lost and the plug-in attempts to make a fresh connection to
another server in the dynamic cluster list. For more information, see Figure 13-1
“Connection Failover” on page 13-14.
Note: If the POST data is larger than 64K, the plugin will not parse the POST data
to obtain the session ID. Therefore, if you store the session ID in the POST
data, the plugin cannot route the request to the correct primary or secondary
server, resulting in possible loss of session data.