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What exactly is Load Balancer, Load Balancer structure and flow (Figure)

Load Balancer, English name Load Balance, is used to distribute operations to multiple execution units for execution. With the continuous increase of network traffic nowadays, Load Balancer of service is necessary. Here, let's talk about the structure of Load Balancer.

When it comes to Load Balancer, nginx may be the easiest thing to think of, but nginx is only one layer, and Load Balancer may start when we send a request. The following is a Load Balancer process:

From the user initiated a request, from DNS diversion, to the middle of the reverse proxy, and then to the application service diversion, experienced a layer by layer, to achieve the purpose of service level expansion, in order to cope with the current huge data traffic.

DNS shunt

DNS function refers to the domain name system, in the World Wide Web, we access other people's services, that is, access to other people's ip, but ip is not easy to remember, at this time the domain name system appeared. Through the mutual mapping of domain names and ip, we can access target services without memorizing ip, but through domain names, and DNS system is a distributed database of domain names and ip addresses mapped to each other. We access domain names and go through the following steps:

There is a mapping relationship between domain names and IPs, but in most cases it is not one-to-one correspondence. We can map multiple IPs to the same domain name, because users access through domain names. The specific address to access is determined by the mapping records of DNS servers and certain Load Balancer algorithms. Users access specific IPs after obtaining them. This process is completely transparent to users. The first step of Load Balancer is completed through DNS offloading:

hardware shunt

Through hardware devices, network traffic is distributed before entering the service, and distributed to different servers through various policies. Common ones such as F5 Load Balancer.

four-layer load

Four-layer load mainly refers to Load Balancer working at the fourth tcp layer in OSI seven-layer model. It mainly selects the server for final processing by modifying the destination address and port in the message and adding a certain Load Balancer policy, such as lvs. It is conceivable that there are layer 2 and layer 3 payloads, which receive requests via virtual mac addresses or virtual ip addresses and then offload them to real mac addresses or ip addresses. These load modes do not care about the specific upper protocol, only responsible for modifying the flow of data.

seven-layer load

The seven-layer load is also called "content load", which is to select specific internal services more intelligently according to the specific application layer content. For example, if there is more URL information requested, select a specific application server to perform corresponding processing, such as nginx.

Client Offloading

The previous Load Balancer, except DNS, has a point to distribute specific traffic, which we call server offloading. When the user request reaches the real application server, the request will be subdivided, and the services of the same type of request may still be clustered, such as today's microservice architecture. At this time, you can use the application framework to complete the offloading of service requests, such as dubbo and springCloud Ribbon components, etc. These offloading methods determined by the service itself are called client offloading.

data layer shunt

Behind the application server is the data layer, various caches, and persistent databases. For requests arriving at the data layer, we can also perform corresponding Load Balancer processing, such as master-slave read-write separation clusters and fragmentation clusters in redis, master-slave read-write, partition tables and databases in mysql, etc.

About A10

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