AWS Execution failed due to configuration error: Authorizer error - amazon-web-services

Question

I created 2 Authorizers to an API Gateway Endpoint. One manually using console and the other one using boto3.
The one created manually works great, however the one created using script gives error mentioned in the subject line. If you check the contents of these 2 authorizers, they are the same.
What can be the missing part? I dont think this is Invalid permission on lambda as it is working on one authorizer when configured manually.
The code for the same is as below:
response = client.create_authorizer(
restApiId=apiid,
name=authName,
type='TOKEN',
authType='custom',
authorizerUri=authorizerUri,
##arn:aws:apigateway:us-west-2:lambda:path/2015-03-31/functions/arn:aws:lambda:us-west-2:<AcctId>:function:CustomAuthorizer/invocations
identitySource='method.request.header.Authorization',
identityValidationExpression= '.*',
authorizerResultTtlInSeconds=300
)
Getting error:
Mon Jul 18 11:53:04 UTC 2016 : Execution failed due to configuration error: Invalid permissions on Lambda function
Mon Jul 18 11:53:04 UTC 2016 : Execution failed due to configuration error: Authorizer error
Mon Jul 18 11:53:04 UTC 2016 : AuthorizerConfigurationException

Answer 1

Just went down this rabbit hole, and came across a solution (worked with boto3 and python, hope it is similar across different sdk's).
The issue is that when you create it manually through the console, there is a popup that asks to enable api gateway (this specific authorizer to be exact) as a trigger to the lambda function you are using as an authorizer. When doing it via sdk, there obviously is no popup, so the authorizer is not authorized to invoke that lambda.
You can enable permissions two ways:
In lambda, create a new trigger for your authorizer in the Designer panel. Specifying an api and stage should do the trick
Create a role that will handle this permission. Give it permission to invoke lambda (you can use the AWSLambdaRole template role) and make sure to add api-gateway as a trusted entity to use this role in the Trust Relationships tab. your policy should look something like this:
{"Version": "2012-10-17","Statement": [{"Effect": "Allow","Principal": {"Service": "apigateway.amazonaws.com"},"Action": "sts:AssumeRole"}]}
Now, when creating a custom authorizer using the sdk, you have to provide an authorizerCredentials parameter, which is described as "(string) Specifies the required credentials as an IAM role for API Gateway to invoke the authorizer. To specify an IAM role for API Gateway to assume, use the role's Amazon Resource Name (ARN). To use resource-based permissions on the Lambda function, specify null.".
Copy your newly-created role's arn and use this as the value for the authorizerCredentials param.
Viola! you now have a custom authorizer that is allowed to use the role that allows it to invoke the lambda function!
(sorry for bad formatting, I don't comment often :D)

Answer 2

First, use the test button in API Gateway to confirm if you can call your Lambda function from within it. This will ensure that the API Gateway-to-Lambda connection is working.
To assess your resource policies, you need to call the GetPolicy API; the execution role controls what your code an do in Lambda, not who can call it. That would be a good next check.
You can also turn on logging in API Gateway, which is a good way to gain additional insight into what it's doing on your behalf. These logs then show up in Amazon CloudWatch Logs, where you can check out the flow of your request.
If you're using CORS, it's possible to miss a setting (or two :), so I would double check that as well. CURLing directly to your endpoint (you can easily test from Lambda using its HTTP endpoint blueprint) is a good first step before you "wire up" your API to a website or other app directly.

Answer 3

It would be helpful if you check your CloudWatch Logs Insights.
Go to your lambda function, open "Monitor" section. Read through the last logs received.
In my case, I made a typo on lambda methods handler address. That is why the error thrown.

Answer 4

You need to add a resource-based statement to your Lambda's permissions, in order to allow it to be called by your gateway. As #MichaelJoy points out, this is taken care of in the console when you click "Create" on the popup. Doing this programmatically requires taking a second step after your authorizer has been created.
To do this via CLI, you can do the following (presumably boto3 has all of the corresponding commands):
aws lambda add-permission --function-name 'arn:aws:lambda:us-west-2:<AcctId>:function:CustomAuthorizer' \
--action lambda:InvokeFunction --statement-id 'api_gateway' \
--principal apigateway.amazonaws.com --output text \
--source-arn "AUTHORIZER_ARN"
where AUTHORIZER_ARN is the ARN of the authorizer you just created. Note that the statement id of 'api_gateway' is arbitrary.
You can see all resource-based policies on your Lambda via the following. This may be helpful esp if you want to inspect the permissions added by you via the console as a working example of what you need to effect programmatically to get the same result:
aws lambda get-policy --function-name XXXX
If you're updating an existing resource-based permission, you'll need to remove it first via the remove-policy command