Microsoft IIS Load Balancing

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Microsoft’s web server Internet Information Services (IIS) is a core component of Windows Server and is estimated to be used by more than 25% of all websites. IIS is built on a modular open architecture that makes it far easier for users to add new features and customize the product through a variety of IIS extensions.

Kemp Technologies LoadMaster Load Balancers and ADCs are full featured layer 4-7 load balancers with content switching, SSL Acceleration and intrusion prevention services for the optimization of Microsoft IIS deployments. The Kemp LoadMaster supports common protocols often utilized in IIS based websites and applications including:

  • HTTP
  • HTTP/2
  • SFTP
  • FTP
  • SMTP
  • NNTP

With IIS Server, LoadMaster can also provide High Availability for:

  • ASP
  • SharePoint
  • OWA (Outlook Web Application)

How Does the Kemp LoadMaster work to Load Balance Microsoft IIS?

The most important function of the LoadMaster is to use load balancing techniques to share the traffic load across an installed base of multiple IIS servers. Thanks to the intuitive, easy to use GUI system, administrators can quickly configure multiple servers and set up their preferred method of traffic load allocation. Clients connect to the LoadMaster rather than directly to individual IIS servers and it is the LoadMaster that decides where to route the client request based upon the selected routing algorithm.

By setting up the network with load balancers between the clients and the IIS servers adding additional capacity becomes very straightforward as it is only necessary configure the additional server into the load balancers stored server list and then it will become operational.

LoadMaster can be deployed as either hardware, bare metal, virtual and in the cloud.


One of the key facilities to set up is persistence that is contained in a database that can be accessed by all IIS servers. Once a user connects the IIS servers can access any information about the users previous session details. As an alternative, the LoadMasters can provide the same service for HTTP traffic where the user’s IP address or cookies allow the LoadMaster to understand the users’ previous history. Both of these methods will allow the clients request to be directed to aback end IIS servers that they have used previously.

While modern pragmatic web application architecture principles recommend that these be built stateless at the transport level and with transactional data available across all application instances for simplicity and native support for cloud infrastructure, many applications in use today were not built with these principles in mind. To this end, LoadMaster provides valuable functionality for highly available IIS frameworks by supporting L4-7 affinity to ensure that client sessions are persisted on the correct instance.

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