Posting SNS message to HTTPS Api Gateway endpoint to trigger Lambda function

Question

I want to trigger a Lambda function in Account2, region2 from Account1, region1 .

So, I use an SNS topic subscribed to an HTTPS API Gateway endpoint (POST method), which will trigger the Lambda.

The problem is that I do not know how to grab the SNS POST request arriving at the API Gateway endpoint .

I am trying to follow this guide from the AWS docs.

I have successfully test the connection between Gateway and Lambda. I use this dummy JSON:

{
  "type": "object",
  "description": "A subscription confirmation message",
  "properties": {
    "SignatureVersion": {
      "enum": [
        "1"
      ],
      "type": "string"
    },
    "Timestamp": {
      "type": "string"
    },
    "MessageId": {
      "type": "string",
      "identity": true
    },
    "SubscribeURL": {
      "type": "string"
    },
    "Token": {
      "type": "string"
    },
    "Signature": {
      "type": "string"
    },
    "Message": {
      "minLength": 1,
      "type": "string",
      "maxLength": 4096
    },
    "Type": {
      "enum": [
        "SubscriptionConfirmation"
      ],
      "type": "string"
    },
    "TopicArn": {
      "type": "string",
      "maxLength": 1224
    }
  }
}

And the test Lambda I use is this:

import boto3,json

def handler(event, context):

    #return event['properties']['SubscribeURL']
    return event

The docs state here that After you subscribe an HTTP/HTTPS endpoint, Amazon SNS sends a subscription confirmation message to the HTTP/HTTPS endpoint.

I don't necessarily want to have a piece of code to confirm the subscription every time because I will only set the flow once. But, I somehow need to take the subscription URL in order to confirm the subscription.

Any pointers would be helpful!

Why not subscribe the Lambda function directly to the SNS topic as an event source, as described here? docs.aws.amazon.com/lambda/latest/dg/… — Mark B
I have tried it but as i understood , both the SNS topic and Lambda function must be in the same region. My use case is to take a manual snapshot of an RDS instance in us-west-2, share it with another account ,so it will be visible in us-west-2 in the 2nd account, and then copy it in us-east-1 in the 2nd account. The Lambda that handles the copy (according to the docs) must be in the region that the copy will live. — Kostas Demiris

RyanG RyanG · Accepted Answer · 2017-01-18T18:54:15

What problem are you trying to solve specifically? You should be able to invoke a Lambda function across accounts using temporary credentials. You could also publish to an SNS topic directly from your Lambda function, so you probably don't need API Gateway.

Posting SNS message to HTTPS Api Gateway endpoint to trigger Lambda function

1 Answers