How to execute more than one lambda in different microservices listening for the cognito PreSignUp event?

Question

Until recently I had a lambda in a microservice that triggered with the cognito PreSignUp event. Now I need to run another one in another microservice, but since I put it in, only one really runs. What do I have to do to be able to execute both, even more lambdas, with the same trigger event?

Answer 1

For anything below, make sure not to take longer than 5 seconds or Cognito will timeout and try the call again up to 3 times.

1. Have a Cognito trigger lambda calling multiple other child lambdas, using invoke()

const lambda = new AWS.Lambda({region: 'us-east-1', apiVersion: '2015-03-31'})

await Promise.all([
  lambda.invoke({
      FunctionName: 'ChildLambda1',
      InvocationType: 'Event',
      LogType: 'None',
      Payload: Buffer.from(JSON.stringify(<DATA HERE>))
    }).promise(),
  lambda.invoke({
      FunctionName: 'ChildLambda2',
      InvocationType: 'Event',
      LogType: 'None',
      Payload: Buffer.from(JSON.stringify(<DATA HERE>))
    }).promise()
])

2. Set a trigger lambda that simply makes API calls to each of the micro-service endpoints that need to be triggered

3. Have each child lambda subscribe to an SNS topic and have the Cognito trigger lambda send a message to said topic (AWS docs)

// SNS subscriptions to "Cognito_PreSignUp" topic are configured in AWS console

// Send message from Cognito trigger lambda
const sns = new AWS.SNS({apiVersion: '2010-03-31'})

await sns.publish({
  Message: JSON.stringify(<DATA HERE>),
  TopicArn: 'Cognito_PreSignUp'
}).promise()