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Tutorial: Create a sample Amazon EventBridge application

You can use EventBridge to route events to specific Lambda functions using rules.

In this tutorial, you’ll use the Amazon CLI, Node.js, and the code in the GitHub repo to create the following:

This example uses Amazon SAM templates to define the EventBridge rules. To learn more about using Amazon SAM templates with EventBridge see Using Amazon Serverless Application Model templates to deploy Amazon EventBridge resources.

In the repo, the atmProducer subdirectory contains handler.js, which represents the ATM service producing events. This code is a Lambda handler written in Node.js, and publishes events to EventBridge via the Amazon SDK using this line of JavaScript code.

const result = await eventbridge.putEvents(params).promise()

This directory also contains events.js, listing several test transactions in an Entries array. A single event is defined in JavaScript as follows:

{
  // Event envelope fields
  Source: 'custom.myATMapp',
  EventBusName: 'default',
  DetailType: 'transaction',
  Time: new Date(),

  // Main event body
  Detail: JSON.stringify({
    action: 'withdrawal',
    location: 'MA-BOS-01',
    amount: 300,
    result: 'approved',
    transactionId: '123456',
    cardPresent: true,
    partnerBank: 'Example Bank',
    remainingFunds: 722.34
  })
}

The Detail section of the event specifies transaction attributes. These include the location of the ATM, the amount, the partner bank, and the result of the transaction.

The handler.js file in the atmConsumer subdirectory contains three functions:

exports.case1Handler = async (event) => {
  console.log('--- Approved transactions ---')
  console.log(JSON.stringify(event, null, 2))
}

exports.case2Handler = async (event) => {
  console.log('--- NY location transactions ---')
  console.log(JSON.stringify(event, null, 2))
}

exports.case3Handler = async (event) => {
  console.log('--- Unapproved transactions ---')
  console.log(JSON.stringify(event, null, 2))
}

Each function receives transaction events, which are logged via the console.log statements to Amazon CloudWatch Logs. The consumer functions operate independently of the producer and are unaware of the source of the events.

The routing logic is contained in the EventBridge rules that are deployed by the application’s Amazon SAM template. The rules evaluate the incoming stream of events, and route matching events to the target Lambda functions.

The rules use event patterns that are JSON objects with the same structure as the events they match. Here's the event pattern for the one of the rules.

{
  "detail-type": ["transaction"],
  "source": ["custom.myATMapp"],
  "detail": {
    "location": [{
      "prefix": "NY-"
    }]
  }
}

Prerequisites

To complete this tutorial, you'll need the following resources:

Step 1: Create application

To set up the example application, you'll use the Amazon CLI and Git to create the Amazon resources you'll need.

Step 2: Run application

Now that you've set up the resources, you'll use the console to test the functions.

Step 3: Check the logs and verify the application works

Now that you've run the application, you'll use the console to check the CloudWatch Logs.

Step 4: Clean up your resources

You can now delete the resources that you created for this tutorial, unless you want to retain them. By deleting Amazon resources that you are no longer using, you prevent unnecessary charges to your Amazon account.