How can i invoke lambda function correctly? [closed] - node.js

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I'm trying to create my first Lambda function on AWS.
I'm following a YouTube tutorial and I wrote the following code in order to get some Users from the DynamoDB online service.
const aws = require('aws-sdk')
aws.config.update({
region : "eu-west-3"
})
const dynamodb = new aws.DynamoDB.DocumentClient()
const dynamoUsersTable = "Users"
const usersPath = "/users"
exports.handler = async (event) => {
console.log('Request event : ', event);
let response;
switch (true) {
case event.httpMethod === 'GET' && event.path === usersPath:
response = await getAllUsers();
break;
default:
break;
}
// UPDATED ANSWER - ADDED RETURN RESPONSE LIGNE ! -> New error : Missing Authentication Token
return response;
}
const buildResponse = (statusCode, body) => {
return {
statusCode : statusCode,
headers : {
"content-type" : "application/json"
},
body : JSON.stringify(body)
}
}
const scanDynamoRecords = async (scanParams, itemArray ) => {
try {
const dynamoData = await dynamodb.scan(scanParams).promise();
itemArray = itemArray.concat(dynamoData.Items);
if (dynamoData.LastEvaluatedKey) {
scanParams.ExclusiveStartkey = dynamoData.LastEvaluatedKey;
return await scanDynamoRecords(scanParams, itemArray);
}
return itemArray;
} catch(error) {
console.error('Do your custom error handling here. I am just gonna log it: ', error);
}
}
const getAllUsers = async () => {
const params = {
TableName: dynamoUsersTable
}
const allUsers = await scanDynamoRecords(params, []);
const body = {
users: allUsers
}
return buildResponse(200, body);
}
But apparently, I get Internal Server Error when I make my GET Request on Postman :
PS: The function has DynamoDBFullAccess Policy and CloudWatch Policy, and I can't find the error message log on cloud watch.
UPDATE: The error was that I had a missing "return" statement after the switch, however and after the fix, "Missing Authentication Token" message is returned as a response from a GET request on Postman. I'm suspecting that IAM has a say in this since I'm using multiple AWS services.

Answer 1

When you create an Lambda function, you define an IAM role that is used to run the Lambda function. If your Lambda function is going to invoke other AWS Services, then you need to create an IAM role that has permissions to invoke those given services. If you do not correctly setup the IAM role permissions, then your Lambda function is not successful.
See this AWS tutorial. Although it is implemented in Java, it covers important information such as setting up an IAM role to invoke AWS services from the Lambda function, and so on.
Creating scheduled events to invoke Lambda functions

Answer 2

You need to return the response variable in your handler method.