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What Is Elastic Load Balance?

Updated at: Nov 01, 2019 GMT+08:00

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

Load Balancer Type

ELB provides two types of load balancers:

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

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

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

Service Architecture

A load balancer distributes incoming traffic across multiple backend servers that reside in one or more availability zones (AZs). You can add one or more listeners to a load balancer.

A 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 rules you define. For an HTTP or HTTPS listener, you can add forwarding policies to forward requests based on the domain name or URL.

A backend server group routes requests to one or more backend servers. You can configure health checks for each backend server group to check the running status of each backend server. When the health check result of a backend server is Abnormal, the load balancer automatically stops routing new requests to this server until it recovers.

Figure 1 ELB components

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 All Services > Network > Elastic Load Balance, or choose Service List > Network > Elastic Load Balance.

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