What is DNS load balancing? Detailed explanation of core concepts and principles

with the rapid development of Internet services, high concurrent access and server overload have become the core bottlenecks restricting business stability. In order to allow users to obtain a smoother access experience and ensure the efficient operation of server clusters, various load balancing technologies have emerged. DNS load balancing is one of the widely used and low-cost implementations. This paper will disassemble the technical details and practical value of DNS load balancing in an all-round way from the core concepts, principles, implementation strategies to practical applications, and provide a systematic reference for technical practitioners and operation and maintenance personnel.

What is the core concept of DNS load balancing?

to understand DNS load balancing, we must first start from the basic functions of DNS, combined with the core goal of load balancing to sort out its definition and essence.

1, the basic definition of DNS load balancing

DNS load balancing is a kind of load balancing technology based on the domain name system, which configures multiple different server Internet Protocol Addresses for the same domain name in the DNS server. When a user initiates a domain name resolution request, the DNS server will return different Internet Protocol Addresses according to the preset policy, and assign user traffic to the corresponding back-end server, so as to realize the traffic sharing of the server cluster.

2, the core goal of DNS load balancing

its core goal is to solve the performance bottleneck problem of a single server, avoid service interruption caused by overload of a single node, and improve the response speed and availability of the overall system. By distributing traffic to multiple servers, it can not only make full use of the hardware resources of the cluster, but also automatically avoid failed nodes through DNS resolution when some servers fail, ensuring the continuous operation of the business.

What is the principle of DNS load balance?

The operation logic of

DNS load balance relies on the basic process of DNS resolution, and realizes traffic distribution through the transformation of resolution rules. This process involves the collaborative operation of multiple key links.

1, domain name and multi-IP binding configuration

operators first need to add multiple A records or AAAA records for the target domain name in the authoritative DNS server, and bind the same domain name to the Internet Protocol Address of multiple servers in the backend cluster. This is the basic configuration of DNS load balancing implementation. Only by completing multi-IP binding can we provide selection space for subsequent traffic allocation.

2, parse the traffic allocation logic of the request

when the user end point initiates a domain name resolution request, the recursive DNS server will query the authoritative DNS server for the Internet Protocol Address corresponding to the domain name. At this time, the authoritative DNS server will select one of the bound multiple Internet Protocol Addresses according to the preset load balancing policy and return it to the recursive DNS server, and then the recursive DNS server will return the Internet Protocol Address to the user end point. The user's subsequent access request will be directly sent to the server corresponding to the IP.

3, automatic avoidance mechanism of fault node

some advanced DNS load balancing services also configure a health check mechanism to regularly check the running status of the back-end server. When a server is found to be malfunctioning and unable to provide services normally, the DNS server will automatically remove the server's Internet Protocol Address from the resolution list until the server returns to normal and then rejoin, thus avoiding user traffic being assigned to the failed node.

What are the mainstream implementation strategies for DNS load balancing?

different business scenarios have different requirements for traffic allocation, DNS load balancing has therefore derived a variety of different implementation strategies to adapt to diverse business needs.

1, polling allocation strategy

polling allocation is the most basic strategy in DNS load balancing. The DNS server will return different IPs to the user in sequence according to the preset Internet Protocol Address sequence. For example, when there are three server IPs, the first user requests to return IP1, the second user requests to return IP2, the third user requests to return IP3, and the fourth user requests to return to IP1, and this cycle. This strategy is simple to implement and suitable for scenarios where each server is configured similarly and the traffic is relatively balanced.

2, weighted polling allocation strategy

weighted polling strategy is optimized on the basis of polling. Operation and maintenance personnel can configure different weight values for different server IPs, and the higher the weight value, the larger the proportion of traffic assigned to the IP. For example, set the weight 3 for the server with a higher configuration, and set the weight 1 for the general server. Then DNS load balance will allocate traffic in a ratio of 3:1, so that the server with stronger performance can bear more access requests and give full play to the value of hardware resources.

3, location-based allocation strategy

this policy will return the Internet Protocol Address of the server closest to the user according to the user's geographical location information. The DNS server will determine the area where it is located through the user's recursive DNS address, and then return the server IP in the area to the user, so as to reduce the delay of network transmission and improve the user's access speed. It is widely used in distributed business scenarios across regions.

What are the practical application scenarios of DNS load balancing?

DNS load balancing has been widely used in many Internet business scenarios by virtue of its simple implementation and no additional hardware equipment, and has become an important technical means to ensure business stability.

1, traffic sharing of small and medium-sized Web sites

for small and medium-sized Web sites, the cost of setting up professional hardware load balancing equipment is high, while DNS load balancing can achieve traffic allocation only by configuring DNS records, which is extremely low cost and easy to operate. The traffic of such websites is relatively controllable, and the polling or weighted polling strategy of DNS load balancing is enough to meet its traffic allocation needs, effectively avoiding overload of a single server.

2, nearby visit

of cross-regional distributed business

in distributed services with multiple geographical nodes, DNS load balancing's geographical location allocation strategy allows users to automatically access the closest node and greatly reduce network latency. For example, the nationwide distributed server cluster of e-commerce platforms allows users in Beijing to access the Beijing node through DNS load balancing, and users in Guangzhou to visit the Guangzhou node to improve the page loading speed and shopping experience of users.

3, emergency disaster recovery of server failure

when a server in the cluster fails, the health check mechanism of DNS load balance will automatically remove the node from the resolution list, distribute subsequent traffic to other normal running servers, and realize the isolation of failed nodes without manual intervention.

sum up, DNS load balancing is a low-cost load balancing technology based on the domain name system. From the core concept to the principle of action, to a variety of implementation strategies and application scenarios, it shows the advantages of strong adaptability and easy operation. Whether it is the traffic sharing of small and medium-sized websites, or the nearby visit of cross-regional services, DNS load balancing can effectively improve the stability and response speed of the system, and is one of the indispensable key technologies in the Internet business architecture.