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What Is ELB?

Updated at: Jul 28, 2021 GMT+08:00

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

ELB Components

ELB consists of the following 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 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 group: routes requests from the load balancer to one or more backend servers. You need to add at least one backend server 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 a backend server is unhealthy, the load balancer stops routing new requests to this server.

Figure 1 ELB components

Load Balancer Type

ELB provides the following types of load balancers: dedicated load balancer, and shared load balancer. Dedicated load balancer and shared load balancer are called elastic load balancers collectively.

  • Shared load balancers are suitable for web services with heavy traffic. Requests are forwarded based on domain names or URLs, making request routing more flexible. Shared load balancers were previously named enhanced load balancers.
  • Dedicated load balancers: You have exclusive use of 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 selection.

Dedicated load balancers are in the OBT in the AP-Singapore, CN-Hong Kong, and AP-Bangkok.

For details about the differences between shared and dedicated load balancers, see Differences Between Shared and Dedicated Load Balancers.

Accessing ELB

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

  • Management console

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

  • APIs

    You can call APIs to access ELB. For details, see the Elastic Load Balance API Reference.

    Dedicated load balancers can be accessed only from the management console for now.

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