A load balancer can distribute incoming traffic across your EC2 instances. This enables you to increase the availability of your application. The load balancer also monitors the health of its registered instances and ensures that it routes traffic only to healthy instances. You configure your load balancer to accept incoming traffic by specifying one or more listeners, which are configured with a protocol and port number for connections from clients to the load balancer and a protocol and port number for connections from the load balancer to the instances.

Elastic Load Balancing supports three types of load balancers: Application Load Balancers, Network Load Balancers, and Classic Load Balancers. You can select a load balancer based on your application needs. For more information, see the Elastic Load Balancing User Guide.

This reference covers the 2012-06-01 API, which supports Classic Load Balancers. The 2015-12-01 API supports Application Load Balancers and Network Load Balancers.

To get started, create a load balancer with one or more listeners using CreateLoadBalancer. Register your instances with the load balancer using RegisterInstancesWithLoadBalancer.

All Elastic Load Balancing operations are idempotent, which means that they complete at most one time. If you repeat an operation, it succeeds with a 200 OK response code.

Installing

To install this package, simply type add or install @aws-sdk/client-elastic-load-balancing using your favorite package manager:

npm install @aws-sdk/client-elastic-load-balancing
yarn add @aws-sdk/client-elastic-load-balancing
pnpm add @aws-sdk/client-elastic-load-balancing

Getting Started

Import

The AWS SDK is modulized by clients and commands. To send a request, you only need to import the ElasticLoadBalancingClient and the commands you need, for example DescribeAccountLimitsCommand:

// ES5 example
const { ElasticLoadBalancingClient, DescribeAccountLimitsCommand } = require("@aws-sdk/client-elastic-load-balancing");

// ES6+ example
import { ElasticLoadBalancingClient, DescribeAccountLimitsCommand } from "@aws-sdk/client-elastic-load-balancing";

Usage

To send a request, you:

Initiate client with configuration (e.g. credentials, region).
Initiate command with input parameters.
Call send operation on client with command object as input.
If you are using a custom http handler, you may call destroy() to close open connections.

// a client can be shared by different commands.
const client = new ElasticLoadBalancingClient({ region: "REGION" });

const params = {
  /** input parameters */
};
const command = new DescribeAccountLimitsCommand(params);

Async/await

We recommend using await operator to wait for the promise returned by send operation as follows:

// async/await.
try {
  const data = await client.send(command);
  // process data.
} catch (error) {
  // error handling.
} finally {
  // finally.
}

Async-await is clean, concise, intuitive, easy to debug and has better error handling as compared to using Promise chains or callbacks.

Promises

You can also use Promise chaining to execute send operation.

client.send(command).then(
  (data) => {
    // process data.
  },
  (error) => {
    // error handling.
  }
);

Promises can also be called using .catch() and .finally() as follows:

client
  .send(command)
  .then((data) => {
    // process data.
  })
  .catch((error) => {
    // error handling.
  })
  .finally(() => {
    // finally.
  });

Callbacks

We do not recommend using callbacks because of callback hell, but they are supported by the send operation.

// callbacks.
client.send(command, (err, data) => {
  // process err and data.
});

v2 compatible style

The client can also send requests using v2 compatible style. However, it results in a bigger bundle size and may be dropped in next major version. More details in the blog post on modular packages in AWS SDK for JavaScript

import * as AWS from "@aws-sdk/client-elastic-load-balancing";
const client = new AWS.ElasticLoadBalancing({ region: "REGION" });

// async/await.
try {
  const data = await client.describeAccountLimits(params);
  // process data.
} catch (error) {
  // error handling.
}

// Promises.
client
  .describeAccountLimits(params)
  .then((data) => {
    // process data.
  })
  .catch((error) => {
    // error handling.
  });

// callbacks.
client.describeAccountLimits(params, (err, data) => {
  // process err and data.
});

Troubleshooting

When the service returns an exception, the error will include the exception information, as well as response metadata (e.g. request id).

try {
  const data = await client.send(command);
  // process data.
} catch (error) {
  const { requestId, cfId, extendedRequestId } = error.$metadata;
  console.log({ requestId, cfId, extendedRequestId });
  /**
   * The keys within exceptions are also parsed.
   * You can access them by specifying exception names:
   * if (error.name === 'SomeServiceException') {
   *     const value = error.specialKeyInException;
   * }
   */
}

Getting Help

Please use these community resources for getting help. We use the GitHub issues for tracking bugs and feature requests, but have limited bandwidth to address them.

Visit Developer Guide or API Reference.
Check out the blog posts tagged with aws-sdk-js on AWS Developer Blog.
Ask a question on StackOverflow and tag it with aws-sdk-js.
Join the AWS JavaScript community on gitter.
If it turns out that you may have found a bug, please open an issue.

To test your universal JavaScript code in Node.js, browser and react-native environments, visit our code samples repo.

Contributing

This client code is generated automatically. Any modifications will be overwritten the next time the @aws-sdk/client-elastic-load-balancing package is updated. To contribute to client you can check our generate clients scripts.

License

This SDK is distributed under the Apache License, Version 2.0, see LICENSE for more information.

Client Commands (Operations List)

AddTags

@aws-sdk/client-elastic-load-balancing