• Elastic Load Balancing

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  2. Elastic Load Balancing
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  4. Service Overview
  5. What Is Elastic Load Balancing?

What Is Elastic Load Balancing?

Elastic Load Balancing (ELB) automatically distributes incoming traffic across multiple backend servers based on the listening configurations and forwarding policies. ELB expands the service capabilities of applications and improves application availability by eliminating single points of failure (SPOFs).

Load Balancer Type

ELB now provides two types of load balancers:

  • Classic load balancer: This type of load balancers can well handle web services with low access traffic and simple applications.
  • Enhanced load balancer: This type of load balancers 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.

Service Architecture

Load balancers receive requests from clients and routes the requests to backend servers in one or more availability zones (AZs).

After creating a load balancer, you need to add at least one listener to it. Listeners use the protocol and port that you have configured to check requests from clients and forward the requests to backend servers in a backend server group using the selected the load balancing algorithm. For HTTP and HTTPs listeners, you can configure forwarding policies to route requests based on domain names or URLs.

Backend server groups each uses the protocol and port that you have specified to forward requests to one or more backend servers.

ELB provides the health check function to check the running status of each backend server. When the health check result of a backend server is Abnormal, ELB automatically stops distributing new requests to this server until it recovers.

Figure 1 Architecture

ELB Access

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

  • Management console

    A graphical user interface has provided for you. To access the service, log in to the management console and choose All Services > Network > Elastic Load Balancing, or choose Service List > Network > Elastic Load Balancing.

  • APIs

    You can also use APIs to send HTTPS requests. This is the most direct way to access ELB. For details, see the Elastic Load Balancing API Reference.