Server Load balancer technology Overview

At present, the development of business volume in Enterprise Networks, campus networks, and wide area networks, such as the Internet, exceeds the most optimistic estimates in the past. The Internet boom is surging and new applications are emerging one after another, even if the network is built according to the optimal configuration at that time, it will soon feel overwhelmed. Especially for the core parts of each network, the large data traffic and computing strength make it impossible for a single device to undertake, however, how can we achieve reasonable service volume allocation among multiple network devices with the same function, so that it does not mean that one device is too busy, but other devices are not able to make full use of the processing capabilities, as a result, the Server Load balancer mechanism came into being.

Based on the existing network structure, Server Load balancer provides a cheap and effective method to expand server bandwidth and increase throughput, enhance network data processing capabilities, and improve network flexibility and availability. It mainly implements the following tasks: solving network congestion problems, providing nearby services to achieve geographic location independence, providing users with better access quality, and improving server response speed; this improves the utilization efficiency of servers and other resources, and avoids spof in key parts of the network.

For Server Load balancer applications of a network, you can start from different network layers. The specific situation depends on the specific analysis of the Network bottleneck, basically, it is achieved from three aspects: transmission link aggregation, higher-level network exchange technology, and server cluster policy setting.

■ Transmission link Aggregation
To support increasing bandwidth applications, more and more PCs use faster links to connect to the network. However, the business volume distribution in the network is unbalanced. The core is high, the edge is low, the key department is high, and the General Department is low. As the computer processing capability is greatly improved, people have higher requirements on the Multi-Working Group LAN processing capability. When the enterprise's internal demand for high-bandwidth applications increases (such as Web access, document transmission, and Intranet connections), data interfaces in the core areas of the LAN will cause bottlenecks, the bottleneck prolongs the response time of customer application requests. In addition, the LAN is scattered, and the network itself has no protection measures for the server. An unintentional action (like kicking the plug of the network cable) will disconnect the server from the network.

Generally, the countermeasure to solve the bottleneck problem is to increase the capacity of the server link so that it exceeds the current demand. For example, you can upgrade from Fast Ethernet to Gigabit Ethernet. For large enterprises, upgrading is a long-term and promising solution. However, for many enterprises, when the demand is not large enough to spend a lot of money and time to upgrade, the use of the upgrade technology is quite useless. In this case, the link aggregation technology provides a low-cost solution to eliminate bottlenecks and insecure factors on the transmission link,

Link aggregation technology combines the transmission capacity of multiple lines into a single logical connection. When the original line cannot meet the requirements, and the upgrade of a single line is too expensive or difficult to implement, it is necessary to adopt a multi-line solution. Currently, there are four link aggregation technologies that can "bundle" multiple lines. The synchronous IMUX system works on the T1/E1 bit layer and uses multiple synchronous DS1 channels to transmit data for load balancing. IMA is another multi-line Reverse Multiplexing Technology that works at the cell level and can run on platforms using ATM routers. Multi-line routing is a popular link aggregation technology. routers can allocate groups to parallel links based on the buffer size (cache) of known destination addresses, you can also use the cyclic Distribution Method to distribute packets to the line. Multi-link PPP, also known as MP or MLP, is a router load balancing technology that uses PPP to encapsulate data links. MP can break down large PPP data packets into small data segments and distribute them to multiple parallel lines. It can also dynamically allocate dialing lines based on the current Link Utilization. Although the speed is very slow, because packet segmentation and additional buffering increase latency, it can run well on low-speed lines.

The link aggregation system increases the complexity of the network, but also improves the reliability of the network, so that people can use redundant routes on the lines of key LAN segments such as servers. VRRP (Virtual routing redundancy protocol) can be used for IP systems ). VRRP can generate a virtual default gateway address. When the master router cannot be connected, the slave router uses this address to continue LAN communication. In short, when the performance of the main line must be improved and the upgrade of a single line is not feasible, the link aggregation technology can be used.

■ Higher level exchange
Large networks are generally composed of a large number of specialized technical devices, such as firewalls, routers, layer-3/layer-3 switches, Server Load balancer devices, buffer servers, and Web servers. How to organically combine these technical devices is a key issue that directly affects network performance. Many vswitches now provide the layer-4 switching function, which can map an external IP address to multiple internal IP addresses and dynamically use one of the internal addresses for each TCP connection request to achieve load balancing. Some protocols support functions related to Server Load balancer, such as redirection in HTTP.


Web content exchange technology, namely URL exchange or layer-7 exchange technology, provides a high-level Control Method for access traffic. The Web content exchange technology checks all HTTP headers, performs load balancing decisions based on information in the header, and determines how to provide services for personal homepage and image data. It is not controlled based on the TCP port number, so it will not cause access traffic to be stranded. If the Web server has been optimized for special features such as image service, SSL conversation, and Database Transaction Service, using this layer of traffic control can improve network performance. Currently, products and solutions using layer-7 switching technology include iSwitch, switches, and Cisco CDN (content exchange network system) of dawn network.

Server Cluster Solution
In some cases, for example, a website's internal staff and external customers use the website at the same time, the company needs to connect the service requests of internal staff to a slow server to provide more resources for external customers. In this case, the Web content exchange technology can be used. Web host access control devices can also use this technology to reduce hardware costs, because it can easily transfer user traffic to multiple hosts to the same Web server. If the user traffic increases to a certain extent, the traffic can also be transferred to dedicated Web server devices, although the cost of such dedicated devices is high, however, because the same Web content exchange technology is used to control traffic, the network structure framework does not need to be changed.

However, the number of standards and rules supported by Server Load balancer devices using Web content exchange technology is limited, and the flexibility of the standards and rules used is limited. In addition, the depth of the HTTP header that the Server Load balancer device can monitor is also a factor limiting the content exchange capability. If the information you are looking for is in a field that cannot be monitored by the Server Load balancer device, content exchange cannot be used. In addition, content exchange is also limited by the number of TCP connections that can be enabled at the same time and the establishment and disconnection ratio of TCP connections. In addition, the Web content exchange technology also occupies a large amount of system resources (including memory usage and processor usage ). Tests on the Web content exchange technology show that it is very labor-intensive to manipulate the Web content throughput, and sometimes it can only get a small performance improvement. Therefore, the network administrator must seriously consider the investment and return issues.

■ Server cluster with a balanced policy
Nowadays, servers must be able to provide a large number of concurrent access services, and their processing and I/O capabilities have become bottlenecks in service provision. If the customer's increase causes the traffic to exceed the capacity of the server, the result must be: downtime. Obviously, the limited performance of a single server cannot solve this problem. The processing capacity of a common server can only reach tens of thousands to hundreds of thousands of requests per second, millions or more requests cannot be processed within one second. However, if a system can be composed of ten such servers and all requests are evenly distributed to all servers through software technology, the system can process millions or more requests every second. This is the initial basic design concept for using Server clusters to achieve load balancing.

Early Server clusters often use fiber optic image cards for master-slave backup. A headache for service operators is that servers with a large number of key servers or applications and large data traffic are generally not too low-grade, the service operator often only gets the performance of one server for the cost of two servers. The new solution is shown in the figure. The LSANT (Load Sharing Network Address Transfer) is used to translate different IP addresses of multiple server NICs into one Virtual IP Address, make each server always in the working status. The work originally required to be completed by a minicomputer was completed by multiple PC servers, this type of elastic solution has a significant effect on investment protection-it not only avoids the huge equipment investment caused by rigid upgrade of minicomputers, but also avoids repeated investment in personnel training. At the same time, service operators can adjust the number of servers at any time according to business needs.

Network Load Balancing improves the availability and scalability of Internet server programs, such as Web servers, FTP servers, and other key task servers. A single computer can provide limited levels of server reliability and scalability. However, by connecting two or more advanced server hosts into a cluster, network load balancing can provide the reliability and performance required by the critical task server.

To create a high-load Web site, the distributed structure of multiple servers must be used. The combination of the proxy server and Web server mentioned above, or the mutual collaboration between the two Web servers, also belongs to the multi-server structure, but in the structure of these multi-server, each server has different roles and is an asymmetric architecture. In an asymmetric server structure, each server plays a different role. For example, one server is used to provide static Web pages, and the other is used to provide dynamic web pages. In this way, the relationship between different servers needs to be considered during webpage design. Once the relationship between servers needs to be changed, connection errors may occur on some webpages, which is not conducive to maintenance and poor scalability.

A load balancing network is designed with a symmetric structure. In a symmetric structure, each server is equivalent and can provide services independently without the assistance of other servers. Then, some technology can be used to evenly distribute external requests to each server in the symmetric structure, and the server that receives the connection request independently responds to the customer's request. In this structure, it is not difficult to establish a completely consistent Web server, so the Server Load balancer technology has become a key technology to build a high-load Web site.

In short, Server Load balancer is a policy that enables multiple servers or multiple links to undertake some heavy computing or I/O tasks? A href = "http://www.bkjia.com/ OS/" target = "_ blank" class = "keylink"> How does the system kill?