Introduction to load balancing in Access Networks

The Access Network Server Load balancer problem has always been a topic of our attention. It does not matter if many people do not know how to solve the Server Load balancer problem. After reading this article, you must have gained a lot, I hope this article will teach you more things. At the beginning, most personal websites may only share a virtual host space with dozens of people and hundreds of people. As the content increases and the access volume increases, the bandwidth and space of the VM cannot meet the requirements, and the webmaster must consider buying an independent server for the website, using M shared or even 10 m of dedicated bandwidth. When the website continues to develop, the number of users to access has also spread across the north and south of the Yangtze River. The webmaster must consider the communication problem between China Telecom and China Netcom.

Each server in the South and North is used as an image site, or two-line access is adopted. When the site has a higher access volume, increasing the bandwidth and setting up an image site will undoubtedly increase the website operation cost, in addition, a single Server also has performance and thread bottlenecks. When the concurrency traffic is large and concentrated on one Server, "Server too busy" appears, in this case, what method should the webmaster use to make the website still have better access results when there is a high traffic volume? This involves the question of Server Load balancer. We have discussed CDN before. In fact, in addition to acceleration, CDN also has the effect of traffic delivery. Therefore, there are also many applications in the field of Server Load balancer, basically Cache) + image technology has the function of shunting, but how to divert is still guided by a Server Load balancer device. Therefore, we will discuss the Server Load balancer technology today.

About Server Load balancer

The server Load balancer service can balance the communication loads between all servers and applications in the server group. It can be judged based on the real-time response time and handed over to the server with the lightest load, to achieve true smart communication management and the best server group performance. Server Load balancer technology controls applications/content from Layer 4 to Layer 7, so as to implement priority division and differentiated services for different types of customers and applications, using Layer 7 Smart session recovery technology, at the same time, HTTP 400,500 and 600 series errors can be detected. It transparently redirects the transaction to another server so that the system can complete the transaction. Server failover and multiple redundancy allow communication to bypass the fault point, so that the website remains running and accessible. There are also many discussions on how to implement Server Load balancer. The following are some references:

1. Server Load balancer based on specific server software

Many network protocols support the "redirection" function. For example, if the Location command is supported in HTTP, the browser that receives the command will automatically redirect to another URL specified by Location. Since sending Location commands is much less load on Web servers than executing service requests, you can design a server with Load Balancing Based on this function.

When the Web server considers itself to be overloaded, it will not directly send back the webpage requested by the browser, but return a Location command, let the browser go to other servers in the server cluster to obtain the required webpage. In this way, the server itself must support this function, but it is difficult to implement it. For example, how can a server ensure that its redirected server is relatively idle, the Location command will not be sent again. Neither the Location command nor the browser has the support capability in this aspect. This makes it easy to form an endless loop in the browser.

Therefore, this method is rarely used in practical applications, and there are few server cluster software implemented using this method. In some cases, you can use CGI (including FastCGI or mod_perl extension to improve performance) to simulate this method to share the load, while the Web server still maintains a concise and efficient feature, in this case, the user's CGI program is responsible for tasks that avoid Location loops.

2. DNS-Based Load Balancing

Server Load balancer Based on server software needs to change the software, so it is often not worth the candle. Server Load balancer should be done out of the server software to take advantage of the advantages of existing server software. The earliest load balancing technology was implemented through random name resolution in the DNS service. In the DNS server, you can configure the same name for multiple different addresses, the client that finally queries the name will get an address when parsing the name. Therefore, for the same name, different customers get different addresses and access the Web servers at different addresses to achieve load balancing.