Implementation of multi-server load balancing with cyclic multiplexing DNS

1 overview

The increase in corporate visibility, web site traffic is gradually rising, is the hope of every network management. But at the same time the application server data traffic and access will multiply, the server will be overwhelmed.

At this point, there are two ways to solve this problem, one is to upgrade the hardware, the purchase of higher configuration, better performance of the server, this method is easy to use, the disadvantage is that the investment is large, will cause the waste of existing resources, and the next increase in business volume will face the same problem. Another approach is to use cluster technology, with more than two servers to work together, the server running in the cluster system is not necessarily high-end products (can be the enterprise existing server), but the server cluster can provide a fairly high-performance non-stop service; In addition, as the volume of business increases, The number of servers running in the cluster system can be increased at any time. The advantages of cluster technology are high reliability and strong flexible system expansion capability.

More than two servers to work together must involve load balancing problem, the current commonly used load balancing technology are: NAT load balancing, reverse proxy load balancing and DNS load.

NAT load Balancing maps an external IP address to multiple internal IP addresses, dynamically converts each connection request to an internal server address, and leads the external connection request to the server on which the address is converted [1]. Reverse Proxy load Balancing uses a proxy server to forward requests to an internal Web server, allowing the proxy server to evenly transfer requests to one of several internal Web servers to achieve load balancing purposes [2]. DNS load balancing configures the same name for multiple addresses in DNS, enabling different clients to access different servers to achieve load balancing. This article will introduce the DNS load balancing principle and technology implementation in detail.

2 DNS Load Balancing principle

DNS load balancing is implemented through cyclic multiplexing, and if multiple address resource records for a host name are found, it can be used to recycle host resource records that are included in the query answer. By default, the DNS server's services use circular multiplexing to sort resource records that are returned in a reply to a host name that resolves to multiple mappings. This feature provides a very easy way to load balance the use of WEB servers and other frequently queried multihomed computers for clients.