Redirect URL through AWS Lambda and CloudFront - node.js

Question

I have a lambda function and I wish to perform a 301 redirect from https://foo.test.com/user_id/bar/ to https://app.test.com/user_id/new
The user's request has an user_id that set as a variable (${userId}) and passed to the target URI (${newUri}).
The value of the user_id is numbers and letters (12-qw12)
I wrote the following code, which sets the ID as a variable and passes it to the Response Headers:
exports.handler = function handler(event, context, callback) {
let request = event.Records[0].cf.request;
let uri = request.uri;
let userId = uri.split('/')[3];
let newUri = `https://app.test.com/` + userId + `/new`;
const response = {
headers: {
'location': [{
key: 'Location',
value: newUri,
}],
},
status: '301',
statusDescription: 'Moved Permanently',
};
callback(null,response);
};
Unfortunately, I get an empty value from the ${userId} that passed to the Response headers:
https://app.test.com//new
If I write the value in the response headers as a string (value: 'https://app.test.com/12-qw12/new') then it works properly.
How can I pass a variable (${userId}) to the response headers without getting an empty value?

Answer 1

You can view the Request Event structure
here:
You can see the actual value of the request URI field by using console.log and checking the respective logs in Cloudwatch.
To print request uri add the folowing the following line before the last two lines in your code:
console.log(Request uri is "${request.uri}");
Then you can know in which index you read userid value.