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What Is Elastic Load Balance?

Updated at:Sep 27, 2020 GMT+08:00

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


  • 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 for requests from clients and route the requests to associated backend servers based on the listening rules you define. You can add one or more listeners to a load balancer.
  • Backend server: a cloud server added to a backend server group to receive requests from the load balancer. At least one backend server must be added to a backend server group.

    You can set a weight for each backend server based on their performance.

    You can also configure health checks for a backend server group to check the health of each backend server. When the health check result of a backend server is Unhealthy, the load balancer automatically stops routing new requests to this server until it recovers.

Figure 1 ELB components

Load Balancer Type

ELB provides two types of load balancers: classic load balancers and shared load balancers.

  • Classic load balancers: can well handle web services with low traffic and simple applications.
  • Shared load balancers: Shared load balancers are renamed from enhanced load balancers. This type of load balancers is suitable for web services with high traffic. Requests are forwarded based on domain names or URLs, making request routing more flexible.

For more information, see Differences Between Classic and Shared Load Balancers.

Currently, classic load balancers are supported only in regions in the Latin America.

Access to ELB

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

  • Management console

    A graphical user interface has been provided for you. To access the service, log in to the management console and choose Network > Elastic Load Balance on the homepage.

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