Coyote Point Systems E350GX, Installation And Administration Manual

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Chapter 1: Equalizer Overview
20 Equalizer Installation and Administration Guide
Introducing Equalizer
Equalizer
®
is a high-performance content switch that features:
• Intelligent load balancing based on multiple, user-configurable criteria
• Non-stop availability with no single point of failure, through the use of redundant servers in a cluster and
the optional addition of a failover (or backup) Equalizer
• Layer 7 content-sensitive routing
• Connection persistence using cookies or IP addresses
• Real-time server and cluster performance monitoring
• Server and cluster administration from a single interface
• SSL acceleration (on Equalizer models with Xcel SSL Hardware Acceleration)
• Data compression (on Equalizer models with Express Hardware GZIP Compression)
• Geographic load balancing (with the optional Envoy software add-on)
This chapter is an introduction to Equalizer’s basic load balancing and application acceleration capabilities, for those
who have some networking experience but may not have previously used an appliance like Equalizer.
Intelligent Load Balancing
Equalizer functions as a gateway to one or more sets of servers organized into virtual clusters . When a client
submits a request to a site that Equalizer manages, Equalizer identifies the virtual cluster for which the request is
intended, determines the server in the cluster that will be best able to handle the request, and forwards the request to
that server for processing.
To route the request, Equalizer modifies the header of the request packet with the appropriate server information and
forwards the modified packet to the selected server. Depending on the cluster options chosen, Equalizer may also
modify the headers in server responses on the way back to the client.
Equalizer support clusters that route requests based on either Layer 4 (TCP or UDP) or Layer 7 (HTTP or HTTPS)
protocols. Layer 4 is also referred to as the Transport Layer , while Layer 7 is referred to as the Application Layer .
These terms come from the OSI and TCP/IP Reference Models, abstract models for network protocol design.
In general, Layer 4 clusters are intended for configurations where routing by the destination IP address of the request
is sufficient and no examination of the request headers is required. Layer 7 clusters are intended for configurations
where routing decisions need to be made based on the content of the request headers. Equalizer evaluates and can
modify the content of request headers as it routes packets to servers; in some cases, it can also modify headers in
server responses on their way back to the client.