AWS Lambda with API gateway and Node.js returning HTTP 502 - node.js

Question

Im testing functionality between AWS Lambda and API gateway. My lambda function is using a Node and I have defined the parameters that i want to be pulling from S3. This is my lambda:
console.log('Loading function');
const aws = require('aws-sdk');
const s3 = new aws.S3({ apiVersion: '2006-03-01' });
exports.handler = async (event, context) => {
const bucket = event.Records[0].s3.bucket.name;
const key = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, ' '));
const params = {
Bucket: 'testing-api-lambda-s3-jfr',
Key: 'sample-file-testing.csv',
};
exports.sendRes = (body, status = 200) => {
const response = {
statusCode: status,
headers: {
"Content-Type": "application/json"
},
body: JSON.stringify(body)
};
return response;
};
The test event on lambda returns OK, so i think lambda its fine:
Test Event Name
test
Response
"text/csv"
Function Logs
START RequestId: 07d8ea41-976b-4e49-9fb7-ccfafca15dcf Version: $LATEST
2022-02-03T19:38:46.871Z 07d8ea41-976b-4e49-9fb7-ccfafca15dcf INFO CONTENT TYPE: text/csv
END RequestId: 07d8ea41-976b-4e49-9fb7-ccfafca15dcf
REPORT RequestId: 07d8ea41-976b-4e49-9fb7-ccfafca15dcf Duration: 499.10 ms Billed Duration: 500 ms Memory Size: 128 MB Max Memory Used: 80 MB
Request ID
07d8ea41-976b-4e49-9fb7-ccfafca15dcf
On my API gateway, i have it configured as GET with no query strings or path parameters defined:
And on the test the error is:
{
"message": "Internal server error"
}
Full API gateway execution logs:
Execution log for request 2866b8b2-bd57-49f7-aad9-1a9279612364
Thu Feb 03 19:44:42 UTC 2022 : Starting execution for request: 2866b8b2-bd57-49f7-aad9-1a9279612364
Thu Feb 03 19:44:42 UTC 2022 : HTTP Method: GET, Resource Path: /
Thu Feb 03 19:44:42 UTC 2022 : Method request path: {}
Thu Feb 03 19:44:42 UTC 2022 : Method request query string: {}
Thu Feb 03 19:44:42 UTC 2022 : Method request headers: {}
Thu Feb 03 19:44:42 UTC 2022 : Method request body before transformations:
Thu Feb 03 19:44:42 UTC 2022 : Endpoint request URI: https://lambda.us-east-1.amazonaws.com/2015-03-31/functions/arn:aws:lambda:us-east-1:143578772304:function:getObjectNode/invocations
Thu Feb 03 19:44:42 UTC 2022 : Endpoint request headers: {X-Amz-Date=20220203T194442Z, x-amzn-apigateway-api-id=vzcwgufch1, Accept=application/json, User-Agent=AmazonAPIGateway_vzcwgufch1, Host=lambda.us-east-1.amazonaws.com, X-Amz-Content-Sha256=ec78e1a3cab036558869aced97bcd18b2213fcab99c7a38ddc15d6bf509a5f5b, X-Amzn-Trace-Id=Root=1-61fc30aa-f6d4b97e6327eed29d022b45, x-amzn-lambda-integration-tag=2866b8b2-bd57-49f7-aad9-1a9279612364, Authorization=*********************************************************************************************************************************************************************************************************************************************************************************************************************************************a0c1a3, X-Amz-Source-Arn=arn:aws:execute-api:us-east-1:143578772304:vzcwgufch1/test-invoke-stage/GET/, X-Amz-Security-Token=IQoJb3JpZ2luX2VjEEQaCXVzLWVhc3QtMSJIMEYCIQDE4SYIymD/u99+1dzLRSk8U+DbUxCC9ygNy6aYr1SjhQIhAN9P2Oh/UyQl1L0mLSNTGhNRFGz2G5irLwGI7gHbs/4eKvoDCHwQABoMM [TRUNCATED]
Thu Feb 03 19:44:42 UTC 2022 : Endpoint request body after transformations: {"resource":"/","path":"/","httpMethod":"GET","headers":null,"multiValueHeaders":null,"queryStringParameters":null,"multiValueQueryStringParameters":null,"pathParameters":null,"stageVariables":null,"requestContext":{"resourceId":"dw7k4w6igh","resourcePath":"/","httpMethod":"GET","extendedRequestId":"M-yKsEC5IAMFegA=","requestTime":"03/Feb/2022:19:44:42 +0000","path":"/","accountId":"143578772304","protocol":"HTTP/1.1","stage":"test-invoke-stage","domainPrefix":"testPrefix","requestTimeEpoch":1643917482625,"requestId":"2866b8b2-bd57-49f7-aad9-1a9279612364","identity":{"cognitoIdentityPoolId":null,"cognitoIdentityId":null,"apiKey":"test-invoke-api-key","principalOrgId":null,"cognitoAuthenticationType":null,"userArn":"arn:aws:iam::143578772304:user/fernando","apiKeyId":"test-invoke-api-key-id","userAgent":"aws-internal/3 aws-sdk-java/1.12.138 Linux/5.4.156-94.273.amzn2int.x86_64 OpenJDK_64-Bit_Server_VM/25.312-b07 java/1.8.0_312 vendor/Oracle_Corporation cfg/retry-mod [TRUNCATED]
Thu Feb 03 19:44:42 UTC 2022 : Sending request to https://lambda.us-east-1.amazonaws.com/2015-03-31/functions/arn:aws:lambda:us-east-1:143578772304:function:getObjectNode/invocations
Thu Feb 03 19:44:42 UTC 2022 : Received response. Status: 200, Integration latency: 24 ms
Thu Feb 03 19:44:42 UTC 2022 : Endpoint response headers: {Date=Thu, 03 Feb 2022 19:44:42 GMT, Content-Type=application/json, Content-Length=261, Connection=keep-alive, x-amzn-RequestId=62424064-5199-48b7-ad4e-f8976d86e514, X-Amz-Function-Error=Unhandled, x-amzn-Remapped-Content-Length=0, X-Amz-Executed-Version=$LATEST, X-Amzn-Trace-Id=root=1-61fc30aa-f6d4b97e6327eed29d022b45;sampled=0}
Thu Feb 03 19:44:42 UTC 2022 : Endpoint response body before transformations: {"errorType":"TypeError","errorMessage":"Cannot read property '0' of undefined","trace":["TypeError: Cannot read property '0' of undefined"," at Runtime.exports.handler (/var/task/index.js:12:33)"," at Runtime.handleOnce (/var/runtime/Runtime.js:66:25)"]}
Thu Feb 03 19:44:42 UTC 2022 : Lambda execution failed with status 200 due to customer function error: Cannot read property '0' of undefined. Lambda request id: 62424064-5199-48b7-ad4e-f8976d86e514
Thu Feb 03 19:44:42 UTC 2022 : Method completed with status: 502
Any suggestions? thank you

Answer 1

The error message from the execution logs says that the event object does not have an array Records with some bucket information. The reason for this is that API Gateway request events do not have this array. API Gateway does not anything about your buckets as long as you do not pass the bucket information in a REST request body.
Moreover, you are expecting a bucket name and key from the API gateway request using these lines:
const bucket = event.Records[0].s3.bucket.name;
const key = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, ' '));
But you never really use these variables anywhere, essentially hardcoding your own bucket name and key with these lines:
const params = {
Bucket: 'testing-api-lambda-s3-jfr',
Key: 'sample-file-testing.csv',
};
Just simply remove these two lines from your code, if you don't need them.
const bucket = event.Records[0].s3.bucket.name;
const key = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, ' '));
I feel like you are confusing how the event object should look like when your Lambda is triggered by an S3 event, compared to what it would look like if the Lambda would be triggered by API Gateway proxy integration. If you want to know the how the event object is structured when the API Gateway invokes it, you may want to check out this page from the AWS docs.

Answer 2

As per the execution logs your API Gateway is not able to transform response received from lambda.
You need to provide your API a model defining response structure such that it can transform responses.
This falls under Mapping templates.
https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-gateway-response-using-the-console.html