Help Center/ Elastic Load Balance/ Service Overview/ What Is ELB?
Updated on 2024-11-14 GMT+08:00
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What Is ELB?

Elastic Load Balance (ELB) automatically distributes incoming traffic across multiple backend servers based on the routing policies you configure. ELB expands the service capabilities of your applications and improves their availability by eliminating single points of failure (SPOFs).

As shown in the example in the following figure, ELB distributes incoming traffic to three application servers, and each server processes one third of the requests. ELB also provides health checks, which can detect unhealthy servers. Traffic is distributed only to servers that are running normally, improving the availability of applications.

Figure 1 Using a load balancer

ELB Components

ELB consists of the components shown in the figure below.

Figure 2 ELB components
Table 1 ELB components

Load balancer

Distributes incoming traffic across backend servers in one or more availability zones (AZs).

Listener

Uses the protocol and port you specify to check requests from clients and route the requests to associated backend servers based on the routing policies and forwarding policies you configure. You can add one or more listeners to a load balancer.

Backend server group

Contains one or more backend servers to receive requests routed by the listener. A backend server can be an ECS, BMS, supplementary network interface, or IP address.

Backend server

Processes requests from the associated load balancer. When you add a listener to a load balancer, you can create or select a backend server group to receive requests from the load balancer by using the port and protocol you specify for the backend server group and the load balancing algorithm you select.

Load Balancer Types

ELB provides shared load balancers and dedicated load balancers.

  • Dedicated load balancers have exclusive access to underlying resources, so that the performance of a dedicated load balancer is not affected by other load balancers. In addition, there are a wide range of specifications available for you.
  • Shared load balancers are deployed in clusters and share underlying resources, so their performance may be affected by other load balancers.

For details about the differences between shared and dedicated load balancers, see ELB Types.

Accessing ELB

You can use either of the following methods to access ELB:

  • Management console

    Log in to the management console and choose Elastic Load Balance (ELB).