How do I subscribe to an event?

Objective: This article explains how to subscribe to an event and configure an AWS lambda function to execute when the event is fired.

Steps:

This article is based on the new event that is demonstrated in How do I add a new event?

1. Add a new AWS serverless function resource and log group in the desired service's event templates file.
   • services/<service>/events/template.yaml
2. Add the service event handler.
   • services/<service>/events/handlers/<function name>/index.ts
   • This is almost always the
3. Add the module event handler logic.
   • modules/<module>/events/handlers/...
4. Register the event handler to the module's event handler builder.
   • modules/<module>/events/handlers.ts
5. Build and test.

Example:

Step 1

# AWS function and log group configuration
# services/<service>/events/template.yaml

Resources:
  ...

  # Lambda function
  MyModelCreatedFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: dist/my-model-created # <-- Must match the file name of the service handler in step 2.
      Handler: index.handler
      FunctionName: my-module-my-model-created
      Timeout: 120
      Policies:
        - Version: '2012-10-17'
          Statement:
            - Effect: Allow
              Action:
                - logs:CreateLogStream
                - logs:DescribeLogStreams
                - logs:PutLogEvents
              Resource: !GetAtt MyModelCreatedLogGroup.Arn
            - Effect: Allow
              Action:
                - cognito-idp:AdminUpdateUserAttributes
              Resource: !Sub 'arn:aws:cognito-idp:${AWS::Region}:${AWS::AccountId}:*'

      Events:
        Trigger:
          Type: EventBridgeRule
          Properties:
            EventBusName: !ImportValue platform-infrastructure-services-event-bus-name
            Pattern:
              source:
                - platform
              detail-type:
                - MyModelCreated # <-- The name of the event

  # Log group
  MyModelCreatedLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Sub /aws/lambda/customers-my-model-created
      RetentionInDays:
        'Fn::If':
          - IsProduction
          - 30
          - 5

Step 2

// Service event handler
// services/<service>/events/handlers/<function name>/index.ts

import { manifest } from '@hectare/platform.modules.customers.events'
import * as Sentry from '@sentry/node'
import { LambdaHandler } from '@hectare/platform.components.context'

const lambdaHandler = new LambdaHandler(manifest)

Sentry.init(lambdaHandler.sentry())

export const handler = async (event: unknown, context: unknown) => {
  await lambdaHandler.handle(event, context)
}

Step 3

// Module event handler
// modules/<module>/events/handlers/my-model-created.ts

import { type EventHandler, Context } from '@hectare/platform.components.context'

export const myModelCreated: EventHandler = async (context: Context): Promise<void> => {
  // TODO: Implement logic here
  console.log('Hello world!')
}

Step 4

// modules/<module>/events/handlers.ts

...

import { myModelCreated as MyModelCreated } from './handlers/my-model-created.js'

const eventHandlers = EventHandlersBuilder.create()
  ...
  .addHandler('MyModelCreated', MyModelCreated)
  .done()

export default eventHandlers

Related Articles:

• How do I add a new event?