Edit AWS SNS message sent to Lambda - amazon-web-services

Question

In my pipeline I have an event notification on an S3 bucket which triggers an SNS topic. That SNS topic in turn has a lambda function subscribed to it. I need the SNS topic to send a hard coded message body to the lambda because it get's used in that function.
Since the SNS topic publishes the message automatically when the S3 event notification is set off I am wondering if and how I can edit the message that gets sent to lambda?
To be clear: I want the same message sent every time. The goal is for lambda to get a variable which is only dependent on which topic the lambda was triggered from.
Currently I am building this through the UI but will eventually code it in terraform for production.

Answer 1

When Amazon SNS triggers an AWS Lambda function, the information it sends includes SNS TopicArn.
You could use that ARN to determine which SNS Topic triggered the Lambda function, and therefore which action it should process.
{
"Records": [
{
"EventSource": "aws:sns",
"EventVersion": "1.0",
"EventSubscriptionArn": "arn:aws:sns:us-east-1:{{{accountId}}}:ExampleTopic",
"Sns": {
"Type": "Notification",
"MessageId": "95df01b4-ee98-5cb9-9903-4c221d41eb5e",
"TopicArn": "arn:aws:sns:us-east-1:123456789012:ExampleTopic",
"Subject": "example subject",
"Message": "example message",
"Timestamp": "1970-01-01T00:00:00.000Z",
"SignatureVersion": "1",
"Signature": "EXAMPLE",
"SigningCertUrl": "EXAMPLE",
"UnsubscribeUrl": "EXAMPLE",
"MessageAttributes": {
"Test": {
"Type": "String",
"Value": "TestString"
},
"TestBinary": {
"Type": "Binary",
"Value": "TestBinary"
}
}
}
}
]
}

Answer 2

Rather than having Amazon S3 send a message to Amazon SNS directly, you might be able to configure an Amazon CloudWatch Events rule that triggers on object creation and sends a Constant as part of the message to Amazon SNS, like this:
If large files are being uploaded, you might also need to trigger it on CompleteMultipartUpload.\
You could also have the rule trigger the AWS Lambda function directly (without going via Amazon SNS), depending upon your use-case. A Constant can also be specified for this.