Coyote Point Systems Equalizer GX Series, Administration Manual

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Overview
Layer 7 Persistence
Equalizer provides server or connection persistence using cookies in Layer 7 HTTP and HTTPS
clusters. The following paragraphs explain connection persistence provided by the appliance, and
its relationship to session persistence.
When a request from a client that has not previously connected to the cluster is received by
Equalizer, it is load balanced according to the current server load values as described in
"Load
Balancing"
on page 29.
However, when a client has existing persistence to a server, Equalizer attempts to put the client
back on that server.
Equalizer can use cookies or a server’s IP address to maintain a persistent session between a
client and a particular server. A cookie, used in Equalizer HTTP and HTTPS clusters contains the
identity of the server that should be used. When a client connects to the cluster for the first time,
Equalizer injects this cookie into the response data. The client’s browser is then responsible for
presenting this cookie back to Equalizer. If Equalizer finds this cookie in the client’s request, it
connects to the server listed.
EQ/OS 10 features "fallback persistence" where Equalizer provide a secondary persistence option
where if, for example, a cookie response is not received, a secondary, or "fallback" option can be
used. As an example, if two persist methods are listed (e.g., Cookie 1:Cluster IP, Server IP /Port
and Source IP)- if a cookie is found- the cookie will be used, otherwise the Source IP of the
incoming connection will be used. If the server with which a client has an unavailable persistent
session, Equalizer automatically selects a different server. Then, the client must establish a new
session; Equalizer stuffs a new cookie in the next response. Details and scenarios are presented
in
"Fallback Persistence Scenarios"
on page 355.
Layer 4 Persistence
For Layer 4 TCP and UDP clusters, Equalizer support IP address-based persistent connections.
With a sticky connection option enabled, Equalizer identifies clients by their IP addresses when
they connect to a cluster. It then routes requests received from a particular client during a
specified period of time to the same server pool 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.
36 Copyright © 2014 Coyote Point Systems, A Subsidiary of Fortinet, Inc.