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.

For circular multiplexing to work correctly, you must first register multiple host resource records for the queried name in this zone and enable the DNS server to be reused. If the DNS server prohibits circular multiplexing, the response order of these queries is based on the static ordering of the resource records in the answer list when they are stored in the zone.

Load Balancing example for 34 servers

Available services: WEB, FTP system to achieve the purpose: to do a more complete load balancing system to share and efficiently use resource equipment status: Five servers, of which four servers composed of cluster systems, IP addresses are 172.28.20.1, 172.28.20.2, 172.28.20.3, 172.28.20.4;

A server as a control Management server, providing DNS services, set enterprise domain name for www.example.com.cn.

Server configuration: Cluster system Server installs Windows Sever, must install Internet Information Service component;

The DNS server installs Windows Sever, and the DNS components must be installed.

⑴ set up each server IP address, subnet mask, gateway and DNS server address, and transfer network.

⑵ set up a DNS server

① creates a standard primary zone for forward lookup in DNS, implementing a domain name

On the DNS server, click Start/Program/Administrative Tools/dns to open the DNS console.

In the console tree, right-click Forward lookup zone, click New Zone/New Area Wizard/Next, and select zone type as standard primary area. If you are not creating a DNS zone on a domain controller in the Active Directory, the "zone integrated with Active Directory" option button in the zone type is unavailable, and click Next.

Enter the name of the zone you want to create example.com.cn, select Create a new zone file with a file name of Example.com.cn.dns, click Next/Finish, and the area example.com.cn appear under forward lookup zones in the console tree.