Load Balancer

Load Balancer creates edge-of-network systems that direct network traffic flow, reducing congestion and balancing the load on various other services and systems. Load Balancer provides site selection, workload management, session affinity, and transparent failover.

Load Balancer is installed between the Internet and the enterprise's back-end servers, which can be content hosts or Caching Proxy machines. Load Balancer acts as the enterprise's single point-of-presence node on the Internet, even if the enterprise uses multiple back-end servers because of high demand or a large amount of content. You can also guarantee high availability by installing a backup Load Balancer to take over if the primary one fails temporarily.

Load Balancer intercepts data requests from clients and forwards each request to the server that is currently best able to fill the request. In other words, it balances the load of incoming requests among a defined set of machines that service the same type of requests. Load Balancer can distribute requests to many types of servers, including WebSphere® Application Servers and Caching Proxy machines. Load balancing can be customized for a particular application or platform by using custom advisors. Special purpose advisors are available to obtain information for load balancing WebSphere Application Servers.

If the Content Based Routing component is installed together with the Caching Proxy, HTTP and HTTPS requests can even be distributed based on URLs or other administrator-determined characteristics, eliminating the need to store identical content on all back-end servers. The Dispatcher component can also provide the same function for HTTP requests.

Load balancing improves your Web site's availability and scalability by transparently clustering content servers, including HTTP servers, application servers, and proxy servers, which are surrogate content servers. Availability is achieved through parallelism, load balancing, and failover support. When a server is down, business is not interrupted. An infrastructure's scalability is greatly improved because back-end processing power can be added transparently.

Load Balancer includes the following components:

Dispatcher

For all Internet services, such as HTTP, FTP, HTTPS, and Telnet, the Dispatcher component performs load balancing for servers within a local area network (LAN) or wide area network (WAN). For HTTP services, Dispatcher can perform load balancing of servers based on the URL content of the client request.

The Dispatcher component enables stable, efficient management of a large, scalable network of servers. With Dispatcher, you can link many individual servers into what appears to be a single virtual server. Your site thus appears as a single IP address to the world.

Content Based Routing

For HTTP and HTTPS services, the Content Based Routing component performs load balancing for servers based on the content of the client request. The Content Based Routing component works in conjunction with the Application Server Caching Proxy component.

Network Address Translation (NAT)

Using Network Address Translation (NAT) Dispatcher capability removes the limitation for the backend servers to be on a locally attached network. This feature is new in Version 8.5.5.

Site Selector

The Site Selector component enhances a load-balancing system by allowing it to act as the point-of-presence node for a network and load balance incoming requests by mapping DNS names to IP addresses. In conjunction with Metric Server, Site Selector can monitor the level of activity on a server, detect when a server has the least amount of network traffic, and detect a failed server.

Cisco CSS Controller

Note:
The Cisco CSS Controller component is shipped with Load Balancer for IPv4, but this component might not support newer hardware. Consult the prerequisites page for supported hardware: http://www.ibm.com/support/docview.wss?rs=180&uid=swg27006921

The Cisco CSS Controller component generates server-weighting metrics that are sent to a Cisco CSS switch for server selection, load optimization, and fault tolerance.

This component is supported on all Edge component installations, with the following exception:

Nortel Alteon Controller

Note:
The Nortel Alteon Controller component is shipped with Load Balancer for IPv4, but this component might not support newer hardware. Consult the prerequisites page for supported hardware: http://www.ibm.com/support/docview.wss?rs=180&uid=swg27006921

The Nortel Alteon Controller component generates server-weighting metrics that are sent to a Nortel Alteon switch for server selection, load optimization, and fault tolerance.

This component is supported on all Edge component installations, with the following exception:

Metric Server

The Metric Server component runs as a daemon on a load-balanced server and provides information about system loads to Load Balancer components.