AWS Lambda - unable to make call to 3rd resource - node.js

Question

I have Lambda Node function behind API Gateway, what I am trying to do is:
Make call to API
Do some logic
Send a message to Slack
Problem:
When I run default test request, the function finishes successfully but it doesn't send a message to Slack (logs only print Slack and not HAHA1/2),however, it does when I run this function from local machine which leads me to believe that AWS stops any none client-server traffic. My function is not in VPC. What can I do to allow outgoing traffic to Slack? Thanks.
const AWS = require('aws-sdk');
const Slack = require('slack-node');
const dynamo = new AWS.DynamoDB.DocumentClient();
/**
* Demonstrates a simple HTTP endpoint using API Gateway. You have full
* access to the request and response payload, including headers and
* status code.
*
* To scan a DynamoDB table, make a GET request with the TableName as a
* query string parameter. To put, update, or delete an item, make a POST,
* PUT, or DELETE request respectively, passing in the payload to the
* DynamoDB API as a JSON body.
*/
sendSlack()
function sendSlack() {
webhookUri = "https://hooks.slack.com/services/....";
slack = new Slack();
slack.setWebhook(webhookUri);
console.log('Slack');
slack.webhook({
channel: "...",
username: "...",
text: "..."
}, function(err, response) {
console.log("HAHA1");
console.log(response);
console.log("HAHA2");
});
}
exports.handler = async (event, context) => {
console.log('Received event:', JSON.stringify(event, null, 2));
sendSlack()
let body;
let statusCode = '200';
const headers = {
'Content-Type': 'application/json',
};
try {
switch (event.httpMethod) {
case 'DELETE':
body = await dynamo.delete(JSON.parse(event.body)).promise();
break;
case 'GET':
body = await dynamo.scan({ TableName: event.queryStringParameters.TableName }).promise();
break;
case 'POST':
body = await dynamo.put(JSON.parse(event.body)).promise();
break;
case 'PUT':
body = await dynamo.update(JSON.parse(event.body)).promise();
break;
default:
throw new Error(`Unsupported method "${event.httpMethod}"`);
}
} catch (err) {
statusCode = '400';
body = err.message;
} finally {
body = JSON.stringify(body);
}
return {
statusCode,
body,
headers,
};
};

Answer 1

You will need to wait for the slack call by either providing a callback or promisifying it:
function sendSlack() {
return new Promise((resolve, reject) => {
webhookUri = "https://hooks.slack.com/services/....";
slack = new Slack();
slack.setWebhook(webhookUri);
console.log('Slack');
slack.webhook({
channel: "...",
username: "...",
text: "..."
}, function(err, response) {
if(err) return reject(err)
resolve(response)
});
})
}
Then in your code
await sendSlack()

Answer 2

It could be that your lambda handler is completing before your call to Slack is successfully executed.
Since the call to Slack is async, I would suggest you try to await its response before your handler returns a response.
I'm not 100% certain, by my guess is that the async Slack call gets scheduled but not run until the main body of the function has completed, at which point the lambda is "spun down" and nothing further is run.