AWS Lambda & SNS: Invoke Lambda cross-region

Question

I have a Lambda function deployed to several regions. I would like to publish a message to SNS that will invoke these functions.

Using aws-cli I've created the topics, given Lambda permission to talk to SNS, and create the subscriptions. The subscription appears to be created successfully, and I can see it in the AWS console. But, it doesn't work. The lambda function does not get invoked.

Have you added the subscription as the event source in the lambda function settings? — Assaf Lavie
Thanks for the question @AssafLavie. I have not done this specifically but I don't believe it's necessary when invoking from SNS or S3. — Shane H
To clarify, I can replicate this in a simpler example by creating an SNS topic with a single subscriber in a different region. In that case I publish a message to the topic but the function is never invoked. It seems permissions related but I can't see anything specific to going inter-region — Shane H

adamkonrad adamkonrad · Accepted Answer · 2016-01-26T15:22:11

This is CloudFormation based example. You have to add invoke permission for SNS to the Lambda functions:

{
    "Type" : "AWS::Lambda::Permission",
    "Properties" : {
        "FunctionName" : { "Fn::GetAtt" : [ "YourLambda", "Arn" ] },
        "Action" : "lambda:InvokeFunction",
        "Principal" : "sns.amazonaws.com",
        "SourceArn" : { "Ref" : "YourSNSTopicArn" }
    }
}

Then you need to subscribe your Lambdas to your SNS topic. This can be done via API call or through CloudFormation.

{
    "Type" : "AWS::SNS::Topic",
    "Properties" : {
        "TopicName" : "YourTopicName",
        "Subscription" : [ {
            "Endpoint" : { "Fn::GetAtt" : [ "YourLambda", "Arn" ] },
            "Protocol": "lambda"
        } ]
    }
}

If you're missing any of this, your Lambdas won't invoke. Source for the above information is the official blog article Invoking Lambda functions via SNS.

AWS Lambda & SNS: Invoke Lambda cross-region

1 Answers