Using AWS Serverless Application Model templates to deploy Amazon EventBridge resources

You can build and test rules manually in the EventBridge console, which can help in the development process as you refine event patterns. However, once you are ready to deploy your application, it’s easier to use a framework like AWS SAM to launch all your serverless resources consistently.

We'll use this example application to look into the ways you can use AWS SAM templates to build EventBridge resources. The template.yaml file in this example is a AWS SAM template that defines four AWS Lambda functions and shows two different ways to integrate the Lambda functions with EventBridge.

For a walkthrough of this example application, see Tutorial: Create a sample Amazon EventBridge application.

There are two approaches to using EventBridge and AWS SAM templates. For simple integrations where one Lambda function is invoked by one rule, the the Combined template approach is recommended. If you have complex routing logic, or you are connecting to resources outside of your AWS SAM template, the Separated template approach is the better choice.

Combined template

The first approach uses the Events property to configure the EventBridge rule. The following example code defines an event that invokes your Lambda function.

Note

This example automatically creates the rule on the default event bus, which exists in every AWS account. To associate the rule with a custom event bus, you can add the EventBusName to the template.

atmConsumerCase3Fn:
  Type: AWS::Serverless::Function
  Properties:
    CodeUri: atmConsumer/
    Handler: handler.case3Handler
    Runtime: nodejs12.x
    Events:
      Trigger:
        Type: CloudWatchEvent 
        Properties:
          Pattern:
            source:
              - custom.myATMapp
            detail-type:
              - transaction                
            detail:
              result:
                - "anything-but": "approved"

This YAML code is equivalent to an event pattern in the EventBridge console. In YAML, you only need to define the event pattern, and AWS SAM automatically creates an IAM role with the required permissions.

Separated template

In the second approach to defining an EventBridge configuration in AWS SAM, the resources are separated more clearly in the template.

1. First, you define the Lambda function:

   atmConsumerCase1Fn:
     Type: AWS::Serverless::Function
     Properties:
       CodeUri: atmConsumer/
       Handler: handler.case1Handler
       Runtime: nodejs12.x

2. Next, define the rule using an AWS::Events::Rule resource. The properties define the event pattern and can also specify targets. You can explicitly define multiple targets.

   EventRuleCase1: 
     Type: AWS::Events::Rule
     Properties: 
       Description: "Approved transactions"
       EventPattern: 
         source: 
           - "custom.myATMapp"
         detail-type:
           - transaction   
         detail: 
           result: 
             - "approved"
       State: "ENABLED"
       Targets: 
         - 
           Arn: 
             Fn::GetAtt: 
               - "atmConsumerCase1Fn"
               - "Arn"
           Id: "atmConsumerTarget1"

3. Finally, define an AWS::Lambda::Permission resource that grants permission to EventBridge to invoke the target.

   PermissionForEventsToInvokeLambda: 
     Type: AWS::Lambda::Permission
     Properties: 
       FunctionName: 
         Ref: "atmConsumerCase1Fn"
       Action: "lambda:InvokeFunction"
       Principal: "events.amazonaws.com"
       SourceArn: 
         Fn::GetAtt: 
           - "EventRuleCase1"
           - "Arn"