Site Selector component

Site Selector acts as a name server that works with other name servers in a domain name system to load balance among a group of servers by using measurements and weights that are gathered. You can create a site configuration to load balance traffic among a group of servers based on the domain name used for a client's request.

[8.5.5.0 or later] A client submits a request for resolution of a domain name to a name server within its network. Name server forwards the request to the Site Selector machine. Site Selector then resolves the domain name to the IP address of one of the servers that is configured under the site name. Site Selector returns the IP address of the selected server to the name server. The name server returns the IP address to the client.

Metric Server is a system monitoring component of Load Balancer that must be installed in each load-balanced server within your configuration. Using Metric Server, Site Selector can monitor the level of activity on a server, detect when a server is the least heavily loaded, and detect a failed server. The load is a measure of how hard the server is working. By customizing system metric script files, you can control the type of measurements that are used to measure the load. You can configure Site Selector to suit your environment, considering such factors as frequency of access, the total number of users, and types of access (for example, short queries, long-running queries, or CPU-intensive loads).

Features of Site Selector:

Functions that provide load balancing

The primary functions of Site Selector interact with each other and your server configuration to balance network traffic in your environment. Site Selector consists of the following functions:
  • The ssserver command handles requests from the command line to the name server, manager, and advisors.
  • The nameserver command works with other name servers in a domain name system to load balance among a group of servers. The name server always runs when the Site Selector component is being used for load balancing.
  • The manager sets weights that are used by the executor, which is based on:
    • Internal counters in the executor
    • Feedback from the servers that are provided by the advisors
    • Feedback from a system-monitoring program, such as Metric Server or WLM.
  • The advisors query the servers and analyze results by protocol before it calls the manager to set weights as appropriate. To configure and manage the name server, advisors, and manager, use the command line (sscontrol) or the graphical user interface (lbadmin).

Managing local and remote servers with Site Selector and Metric Server

A client submits a request for resolution of a domain name to a client name server. The client name server forwards the request through the DNS to the Site Selector machine (Path 1). Site Selector then resolves the domain name to the IP address of one of the servers. Site Selector returns the IP address of the selected server to the client name server. The name server returns the IP address to the client. After the client receives the IP address of the server, the client routes application requests directly to the selected server (Path 2).
Important: In this example, the Metric Server provides system load information to the Site Selector machine. The Metric Server agent is installed on each backend server. Use Metric Server with Site Selector; otherwise Site Selector can use only a round-robin selection method for load balancing.
This figure illustrates a site in which the Site Selector component is used to answer requests. Server1, Server2, and Server3 are local. Server4, Server5, and Server6 are remote.
Example of a site that uses Site Selector and Metric Server to manage local and remote servers
Concept topic    

Terms and conditions for information centers | Feedback

Last updated: April 16, 2014 11:59 AM EDT
File name: covr_siteselector.html