AWS Lambda
Developer Guide

Using AWS Lambda with Amazon SNS

You can use a Lambda function to process Amazon Simple Notification Service notifications. Amazon SNS supports Lambda functions as a target for messages sent to a topic. You can subscribe your function to topics in the same account or in other AWS accounts.

Amazon SNS invokes your function asynchronously with an event that contains a message and metadata.

Example Amazon SNS Message Event

{ "Records": [ { "EventVersion": "1.0", "EventSubscriptionArn": "arn:aws:sns:us-east-2:123456789012:sns-lambda:21be56ed-a058-49f5-8c98-aedd2564c486", "EventSource": "aws:sns", "Sns": { "SignatureVersion": "1", "Timestamp": "2019-01-02T12:45:07.000Z", "Signature": "tcc6faL2yUC6dgZdmrwh1Y4cGa/ebXEkAi6RibDsvpi+tE/1+82j...65r==", "SigningCertUrl": "", "MessageId": "95df01b4-ee98-5cb9-9903-4c221d41eb5e", "Message": "Hello from SNS!", "MessageAttributes": { "Test": { "Type": "String", "Value": "TestString" }, "TestBinary": { "Type": "Binary", "Value": "TestBinary" } }, "Type": "Notification", "UnsubscribeUrl": "", "TopicArn":"arn:aws:sns:us-east-2:123456789012:sns-lambda", "Subject": "TestInvoke" } } ] }

For asynchronous invocation, Lambda queues the message and handles retries. If Amazon SNS is unable to reach Lambda or the message is rejected, Amazon SNS retries at increasing intervals over several hours. For details, see Reliability in the Amazon SNS FAQ.

In order to perform cross account Amazon SNS deliveries to Lambda, you need to authorize your Lambda function to be invoked from Amazon SNS. In turn, Amazon SNS needs to allow the Lambda account to subscribe to the Amazon SNS topic. For example, if the Amazon SNS topic is in account A and the Lambda function is in account B, both accounts must grant permissions to the other to access their respective resources. Since not all the options for setting up cross-account permissions are available from the AWS console, you use the AWS CLI to set up the entire process.

For more information, see Invoking Lambda functions using Amazon SNS notifications in the Amazon Simple Notification Service Developer Guide.