Planning server load balancing
A key part of HA, server load balancing provides technologies that can improve the resiliency of any IIS-based web farm, SharePoint included.
Server load balancing is a technology that has been around for over a decade. At a very basic level, the role of load balancing is simply to distribute incoming web requests across multiple web servers; you could do a very similar thing via round-robin DNS.
Any load balancer intended for use with SharePoint requires the capability to set up persistent/sticky/affinity sessions. Failure to properly configure affinity does not immediately manifest itself in problems, but causes problems with technologies such as Kerberos, SSL, and
forms authentication.
Web tier load balancing
Web tier load balancing is accomplished via one of two technologies:
■■ Windows Network Load Balancing (NLB)
■■ Hardware load balancing
Windows Network Load Balancing (NLB) is a feature that can be activated from within the Add Roles And Features Wizard of Server Manager. This feature distributes incoming traffic across a series of web servers using the TCP/IP networking protocol.
In this type of load balancing, a virtual IP address is assigned to multiple servers at once. Although each web server is capable of responding to a single HTTP/HTTPS request, it is recommended that affinity be set up in load balancing so a user who starts a session with a particular web server stays with that server until the end of the session.
Because this is a built-in server feature, hardware and operating system resources are consumed in order for load balancing to operate, and this feature must be monitored along with the rest of the server functionality. As new web servers are added into the SharePoint farm, it is necessary for an administrator familiar with the load balancing services to configure this feature on any new server.
Although Windows NLB is quite durable, hardware load balancers are often preferred in larger enterprise server environments. These environments tend to acquire an administrator familiar with the specific skills required by the manufacturer of a dedicated load balancing system.
There are several reasons for building a dedicated load balancer layer within your organization:
■■ Centralized administration of load balancing.
■■ Performance impact of load balancing is not present on web servers.
■■ Multiple service types (Citrix, web servers, and so on) can be presented by the load balancing system.
