In this article, we learned how to fix the 'failed to fetch' error from API-Gateway in our AWS Lambda Serverless Framework. The root cause is ended up to be the expired AWS Cognito Access/ID tokens. We were able to fix this by utilizing the Apollo Error Link to replace the old token with the refreshed one, and then retry the request.
AWS provides us Amazon Cognito User Pools, which could be used as authorizer to control access to our application. The article will explain all three tokens implemented by Cognito User Pools, and discuss some common questions of how to use those tokens.