Api Gateway can't invoke Lambda function

Question

Following this tutorial on AWS, I hit a roadblock when trying to test the api through the web console (as many others did):

Thu Nov 10 22:54:48 UTC 2016 : Execution failed due to configuration error: Invalid permissions on Lambda function

I've read every relevant post on SO and AWS forums I could find, but can't figure out how to grant permission to the API Gateway to invoke the Lambda function.

Answer 1

Web Console Method:

Thanks to this mate I found a quick fix:

Go into the web console and select

The resource method > Integration Request > Pencil next to Lambda Function > Check mark next to lambda function (don't change the name)

A popup window should warn that you are granting permissions to the API to execute the lambda function.

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API Method:

Also, thanks to Richard Downer for this code explanation:

A resource policy is different from an IAM Policy, setting the IAM policy will not work.

You need to use the Add-LMPermission api call after creation of Write-AGIntegration.

Here is an example:

Add-LMPermission -FunctionName myfunction -Action lambda:InvokeFunction -Principal apigateway.amazonaws.com -SourceArn arn:aws:execute-api:us-west-2:IAMAccountNumber:*/*/POST/apiendpoint -StatementId description

• JBaczuk: Amen. I called AWS the other day after hours of struggling and they said, oh, our documentation is wrong, do this...
• b01: How can you add this policy with terraform or through the console?
• Salvador Hernandez: I imported API via Swagger...but forgot to update the permissions for lambda invocation, this fixed my issue!
• hikarunoryoma: you can add this through terraform via this resource: resource "aws_lambda_permission" "<resource_name>" { statement_id = "AllowAPIgatewayInvocation" action = "lambda:InvokeFunction" function_name = "<function_name>" principal = "apigateway.amazonaws.com" source_arn = "arn:aws:execute-api:us-east-1:<account_id>:*/*/*" }