Invoke a lambda function when another lambda function is deployed

Question

I have an AWS lambda function that provides configuration objects. Whenever this lambda function is updated(i.e deployed again), I need to trigger another lambda function, that detects changes in those config objects and takes some action. How do I monitor this lambda deployment, which cloud watch event do I need to subscribe to?

Answer 1

I assume that your lambda deployments are not managed by CodeDeploy. If so, I would recommend looking into creating a CloudTrial trial.

Once CT trial is created with default settings, it will monitor all management API calls to your lambda function. One of them is UpdateFunctionCode. Thus you can create a CloudWatch rule for AWS API Call via CloudTrail. The rule would be triggered on the function update API call.

Example of such a rule:

{
  "source": [
    "aws.lambda"
  ],
  "detail-type": [
    "AWS API Call via CloudTrail"
  ],
  "detail": {
    "eventSource": [
      "lambda.amazonaws.com"
    ],
    "eventName": [
      "UpdateFunctionCode"
    ]
  }
}

Then you can trigger a second lambda, based on the captured update event of the first function.

Answer 2

Based on @Marcin's suggestion, used console log to print the event. The below rule helped to filter a specific function;

{
  "source": [
    "aws.lambda"
  ],
  "detail-type": [
    "AWS API Call via CloudTrail"
  ],
  "detail": {
    "eventSource": [
      "lambda.amazonaws.com"
    ],
    "eventName": [
      "UpdateFunctionCode20150331v2"
    ],
    "responseElements": {
      "functionName": [
        "myFunction"
      ]
    }
  }
}