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About Web publishing load balancing

Published: November 15, 2009

Updated: February 1, 2011

Applies To: Forefront Threat Management Gateway (TMG)

In Forefront TMG, when you publish a farm of Web servers that perform the same role or host the same content, you can enable high availability for inbound access by configuring Forefront TMG to control the load balancing among the servers in the farm. Load balancing ensures that requests are distributed evenly among the available Web servers, detects offline servers, implements failover, and maintains farm servers, without disrupting current endpoint connections.

Forefront TMG load balancing ensures that traffic is distributed evenly between farm servers, by using the following mechanisms:

  • Round-robin mechanism—By spreading requests from different IP addresses evenly among the Web farm members, the round-robin mechanism ensures that user requests to a Web application serviced by a Web farm are distributed evenly among farm members that are online. This even spread is preserved during failover. When failover occurs, servers that are not responding are detected, and the load is distributed among the available servers.

  • Affinity—Forefront TMG ensures that, after a user has been routed once to a particular application server, the user continues to be routed to that server. Forefront TMG supports two load balancing affinity types:

    • Cookie-based load balancing, or session affinity—User session is associated with the server. It is recommended that you use session affinity whenever possible, because it provides a more reliable affinity when a Web server is restarted.

    • Source-IP-based load balancing, or IP affinity—Client IP address is associated with the server. This type of affinity should be used in an Exchange RPC-over-HTTP publishing scenario, where session affinity cannot be used because cookies are not supported by the Outlook client application.

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