Coyote Point Systems E350GX, Руководство по установке и администрированию

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Chapter 1: Equalizer Overview
24 Equalizer Installation and Administration Guide
uniquely identifies the server to which the client was just connected. The client includes (sends) the cookie in
subsequent requests to the Equalizer. Equalizer uses the information in the cookie to route the requests back to the
same server.
Equalizer can direct requests from a particular client to the same server, even if the connection is to a different
virtual cluster. For example, if a user switches from an HTTP cluster to an HTTPS cluster, the persistent cookie will
still be valid if the HTTPS cluster contains a server with the same IP address.
If the server with which a client has a persistent session is unavailable, Equalizer automatically selects a different
server. Then, the client must establish a new session; Equalizer stuffs a new cookie in the next response.
IP-Address Based Persistence (Layer 4)
For Layer 4 TCP and UDP clusters, Equalizer supports IPaddress based persistent connections. With the sticky
connection feature enabled, Equalizer identifies clients by their IP addresses when they connect to a cluster.
Equalizer then routes requests received from a particular client during a specified period of time to the same server
in the cluster.
A sticky timer measures the amount of time that has passed since there was a connection from a particular IP address
to a specific cluster. The sticky time period begins to expire as soon as there are no longer any active connections
between the client and the selected cluster. Equalizer resets the timer whenever a new connection occurs. If the client
does not establish any new connections to the same cluster, the timer continues to run until the sticky time period
expires. At expiration, Equalizer handles any new connection from that client like any other incoming connection
and routes it to an available server based on the current load balancing policy.
To correctly handle sticky connections from ISPs that use multiple proxy servers to direct user connections,
Equalizer supports
sticky network aggregation , which uses only the network portion of a client's IP address to
maintain a persistent connection. Sticky network aggregation directs the user to the same server no matter which
proxy he or she connects through.
You can also configure Equalizer to ensure that it directs requests from a particular client to the same server even if
the incoming connection is to a different virtual cluster. When you enable
intercluster stickiness for a cluster,
Equalizer checks the cluster for a sticky record as it receives each connection request, just like it does for ordinary
sticky connections. If Equalizer does not find a sticky record, Equalizer proceeds to check all of the other clusters
that have the same IP address. If Equalizer still does not find a sticky record, it connects the user based on the
current load balancing policy.
Is Connection Persistence Always Needed With Session Persistence?
Session persistence is a function of the application and the state created when a user logs into a web site. If the
session persistence is maintained in the front end server, then Equalizer cookie persistence should be enabled. The
client must maintain the connection to the same front end server in order for the login to remain valid. For example,
Windows Terminal Services maintains a session directory "database" when a user logs into a session. If that state or
database is in the front end server, or even in a back end server that only associates the client connection to that front
end server, then the client must "persist" to the front end server to which it is originally connected.
In other configurations, the session "state" is kept in shared storage in a backend server or database that is accessible
to all the front end servers. If this is the case, then connection persistence may not be needed; if the user is balanced
among servers, then the session can still be maintained across the front end server group via access to the shared
storage.
It’s therefore important to understand how the load balanced application provides session persistence when
managing persistent connections on Equalizer.
Layer 7 Load Balancing and Server Selection
Equalizer’s support for Layer 7 content-sensitive load balancing enables administrators to define rules for routing
HTTP and HTTPS requests, depending on the content of the request. Layer 7 load balancing routes requests based