[AWS

1. Create a Lambda function, because we want to work with Application Load Balancer, we need to give a different response from Lambda

Check: https://docs.aws.amazon.com/lambda/latest/dg/services-alb.html

exports.handler = async (event) => {
    console.log('event', event);
    // TODO implement
    const response = {
        "statusCode": 200,
        "statusDescription": "200 OK",
        "isBase64Encoded": false,
        "headers": {
            "Content-Type": "text/html"
        },
        "body": "<h1>Hello from Lambda!</h1>"
    };
    return response;
};

2. Create "Target Groups", because Lambda must be inside a Target Group in order to work with ALB.

3. After Target Group becomes `Active`, we can open DNS name in broswer and we should see `Hello from Lambda!` in the page

4. Enable "Multi-values header" in Target Group

5. in browser, we can enable url like `http://myalb-labmda-xxxxxx.us-east-1.elb.amazonaws.com/?name=foo&name=bar`

Noice that it downs the response, but actually we don't want that, we need to modify Lambda response according to:

https://docs.aws.amazon.com/elasticloadbalancing/latest/application/lambda-functions.html#multi-value-headers-response

exports.handler = async (event) => {
    console.log('event', event);
    // TODO implement
    const response = {
        "statusCode": 200,
        "statusDescription": "200 OK",
        "isBase64Encoded": false,
        "headers": {
            "Content-Type": "text/html"
        },
        "multiValueHeaders": {
              "Set-cookie": ["cookie-name=cookie-value;Domain=myweb.com;Secure;HttpOnly","cookie-name=cookie-value;Expires=May 8, 2019"],
              "Content-Type": ["text/html"]
        },
        "body": "<h1>Hello from Lambda!</h1>"
    };
    return response;
};

6. Check from CloudWatch:

2021-06-03T05:43:17.696Z    5f01fe7f-b7bb-4906-8af7-77579b189a55    INFO    event {
  requestContext: {
    elb: {
      targetGroupArn: 'arn:aws:elasticloadbalancing:us-east-1:xxxxxxxx:targetgroup/myTG-ALB/03b5bf1b78f9e5ac'
    }
  },
  httpMethod: 'GET',
  path: '/',
  multiValueQueryStringParameters: { name: [ 'foo', 'bar' ] },
  multiValueHeaders: {
    accept: [
      'text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9'
    ],
    'accept-encoding': [ 'gzip, deflate' ],
    'accept-language': [ 'en-GB,en;q=0.9' ],
   ....

  },
  body: '',
  isBase64Encoded: false
}