Lambda function not working with cloud formation deploy - amazon-web-services

Question

I am trying to build out an app with an api gateway and a node back end running on lambda.
The node backend is very basic with express and sequelize. It isn't hooked up to a database yet. I can run the node app locally, navigate to an end point and get the standard "hello world" response that I send back from that end point.
When I build and deploy the stack, it shows that the code deployed to an s3 bucket and that the api and lambda were updated. However, I get the following error when trying to access an end point -
502 Bad Gateway - "message": "Internal server error"
Again, there is no logic on the back end, just a text response sent back. I have no idea how to address this. It doesn't seem to be an API issue, although I don't know how to test that. If it is an issue with the lambda deploy, why does it work locally?
In addition to this, the api gateway created by the cloudformation file has a "dev" stage and a "Stage" stage. I am not sure how this happened or if it is a problem.
Below is the yaml file.
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: Storygraf backend API
Globals:
Function:
Timeout: 3
Resources:
ExpressApi:
Type: AWS::Serverless::Api
Properties:
StageName: dev
ExpressLambdaFunction:
Type: AWS::Serverless::Function
Properties:
CodeUri: s3://storygraf-backend/xxxx
Handler: lambda.handler
MemorySize: 512
Runtime: nodejs14.x
Timeout: 30
Events:
ProxyApiRoot:
Type: Api
Properties:
RestApiId:
Ref: ExpressApi
Path: /
Method: ANY
ProxyApiGreedy:
Type: Api
Properties:
RestApiId:
Ref: ExpressApi
Path: /{proxy+}
Method: ANY

Answer 1

You should activate logs to be able to troubleshoot:
ExpressApi:
Type: AWS::Serverless::Api
Properties:
StageName: dev
MethodSettings:
- ResourcePath: "/*"
HttpMethod: "*"
DataTraceEnabled: true
LoggingLevel: INFO # Or ERROR
OpenApiVersion: 3.0.1 # This will remove the stage Stage
Note about OpenApiVersion:
Note: Setting this property to any valid value will also remove the stage Stage that SAM creates.
Then copy your apiId:
Send your request to your API and go to CloudWatch, there should be a Log Group named API-Gateway-Execution-Logs_{apiId}/dev (you can paste your apiId in the search box to find it).
In there you can see detailed logs about the request and integration.
You most likely have an error like:
Execution failed due to configuration error: Malformed Lambda proxy response
Because lambda response should at least contain a statusCode field:
With the Lambda proxy integration, the Lambda function must return output of the following format:
statusCode: "...", // a valid HTTP status code
headers: {
custom-header: "..." // any API-specific custom header
},
body: "...", // a JSON string.
isBase64Encoded: true|false // for binary support } ```
See API Gateway developer guide and specifically:
Getting Started
Integration Response
Lambda Integration