"internal server error" with API gateway and lambda on AWS

Question

There are tons of similar questions both on this site and on the web, which leads me to believe there is something really wrong with AWS' documentation due to this causing grief to so many people.

So, I decided to post the most basic example step by step.

First, we create a new function:

It has default "everything", I don't touch a single line of code.

(the red error message is AWS not playing nice with Firefox)

The default code passes the test:

Now I add a trigger:

This gives me the link for the trigger:

I can go to the API endpoint: https://spy3z1jvu8.execute-api.ap-northeast-1.amazonaws.com/default/test

And it works:

Now, the problems will start. I open the API gateway that was created:

and try the default link: https://spy3z1jvu8.execute-api.ap-northeast-1.amazonaws.com

And...

Most of the people having similar questions seem to be having an issue with the gateway expecting some json content, etc, but here is an untouched AWS sample and the gateway link doesn't work.

The troubleshooting steps say to add logging and troubleshoot it that way, but there is nothing of interest in the logs.

What could be the origin of that problem?

Answer 1

What could be the origin of that problem?

You are correct. This is AWS/console fault. Specifically, it provides wrong permissions in the lambda's resource-based permissions for the default route to work. To fix that you have to edit the permissions .

Specifically, go to your function's Resource-based policy (this is different then execution role). You should find one Policy statement there which you have to edit. Then change in Source ARN from something like:

arn:aws:execute-api:ffffff:xxxx:api-id/*/*/function-name

to

arn:aws:execute-api:ffffff:xxxx:api-id/*/*