Forward requests to internal service lambda AWS - node.js

Question

I need to forward a http request recieved to a lambda function to another url (ECS service) and send back the response.
I manage to achieve this behaviour with the following code:
exports.handler = async (event) => {
const response = {
statusCode: 302, // also tried 301
headers: {
Location: 'http://ec2-xx-yy-zz-ww.us-west-x.compute.amazonaws.com:2222/healthcheck'
}
};
return response;
};
It seems to work, but this changes the original url (which is like toing.co:5500) to the redirected aws url.
So I tried to create an async request inside lambda that would query and return the response:
const http = require('http');
const doPostRequest = () => {
const data = {};
return new Promise((resolve, reject) => {
const options = {
host: 'http://ec2-xx-yy-zz-ww.us-west-x.compute.amazonaws.com:5112/healthcheck',
port: "2222",
path: '/healthcheck',
method: 'POST'
};
const req = http.request(options, (res) => {
resolve(JSON.stringify(res.statusCode));
});
req.on('error', (e) => {
reject(e.message);
});
//do the request
req.write(JSON.stringify(data));
req.end();
});
};
exports.handler = async (event) => {
await doPostRequest()
.then(result => console.log(`Status code: ${result}`))
.catch(err => console.error(`Error doing the request for the event: ${JSON.stringify(event)} => ${err}`));
};
but I get a bad gateway (502) error for this. How can I implment a simple forwarder for post requests (with a message body)?

Answer 1

The issue was that the response from the lambda function was a plain json string and not html (as pointed out by #acorbel), hence the load balancer could not process the response, resulting in a 502 error.
The solution was to add http headers and a status code to the response:
const http = require('http')
let response = {
statusCode: 200,
headers: {'Content-Type': 'application/json'},
body: ""
}
let requestOptions = {
timeout: 10,
host: "ec2-x-xxx-xx-xxx.xx-xx-x.compute.amazonaws.com",
port: 2222,
path: "/healthcheck",
method: "POST"
}
let request = async (httpOptions, data) => {
return new Promise((resolve, reject) => {
let req = http.request(httpOptions, (res) => {
let body = ''
res.on('data', (chunk) => { body += chunk })
res.on('end', () => { resolve(body) })
})
req.on('error', (e) => {
reject(e)
})
req.write(data)
req.end()
})
}
exports.handler = async (event, context) => {
try {
let result = await request(requestOptions, JSON.stringify({v: 1}))
response.body = JSON.stringify(result)
return response
} catch (e) {
response.body = `Internal server error: ${e.code ? e.code : "Unspecified"}`
return response
}
}