Application of load balancing technology in high load Web site

The rapid growth of the Internet makes multimedia network servers, especially the http://www.aliyun.com/zixun/aggregation/17117.html ">web servers, face a rapid increase in the number of visitors, Network servers require the ability to provide a large number of concurrent access services. For example, Yahoo receives millions of requests per day for access, so CPU, I/O processing capacity will quickly become a bottleneck for servers that provide large-load Web services.

In some large networks, due to the differences in hardware devices, sizes and services provided within multiple server clusters, we can consider the most appropriate load balancing method for each server cluster. Then again, load-balanced or clustered across the multiple server clusters to provide services to the outside world (that is, to treat these multiple server groups as a new server farm) for optimal performance. We call this approach a hybrid load-balancing. This approach is sometimes used in situations where the performance of a single equalization device cannot satisfy a large number of connection requests.

The normal proxy is a connection request that the agent's internal network user accesses to the server on the Internet, and the client must specify a proxy server and send a connection request that would have been sent directly to the server on the Internet to the proxy server for processing. A reverse proxy (Reverse proxy) means to accept a connection request on the Internet with a proxy server, then forward the request to a server on the internal network and return the results obtained from the server to the client requesting the connection on the Internet, At this point the proxy server behaves as a server. The reverse proxy load balancing technique is to dynamically transfer the connection requests from the Internet to multiple servers on the internal network in a reverse proxy way to achieve load balancing.

Simple to improve hardware performance does not really solve this problem, because the performance of a single server is always limited, generally speaking, a PC server can provide more than 1000 concurrent access processing capacity, more high-end dedicated server to support 3000-5000 concurrent access, This ability is still unable to meet the requirements of the larger web site. In particular, network requests are abrupt, when some major events occur, network access will rise sharply, resulting in network bottlenecks, such as the online release of the Clinton impeachment is a clear example. You must use multiple servers to provide network services and allocate network requests to these server shares to provide the ability to handle a large number of concurrent services.

When using multiple servers to share the load, the easiest way is to use different servers in different ways. When split by the provided content, you can use one server to provide a news page, another to provide a game page, or you can split by server functionality, use one server to provide static page access, and others to provide dynamic page access that requires a lot of resource consumption, such as CGI. However, due to the sudden network access, making it difficult to determine those pages caused by the load is too large, if the service of the page segmentation will cause a lot of waste. In fact, the heavy load of the page is often in the change, if you want to constantly follow the load changes to adjust the page of the server, then the management and maintenance will cause great problems. So this segmentation method can only be the general direction of adjustment, for large load of the site, the fundamental solution also need to apply load balancing technology.

Load balancing the idea of a number of servers in a symmetrical manner, each server has the equivalent status, can be a separate external service without the support of other servers. Then, through some kind of load-sharing technology, the externally sent requests are evenly distributed to one of the servers in the symmetric structure, and the server receiving the request responds independently to the client's request. Because the content of the Web server is not complex, the server can be synchronized update or shared storage space and other methods to complete, so load balancing technology becomes a high load of the Web site's key technology.