AWS VPC instance doesn't resolve public DNS name

Question

The problem:

My url xyz.co is getting resolved into an ugly AWS public DNS name such as ec2-11-22-33-44.ap-southeast-2.compute.amazonaws.com. It doesn't stick to xyz.co.

Here's what I did:

I have set up my Route 53 configuration according to http://docs.aws.amazon.com/Route53/latest/DeveloperGuide/MigratingDNS.html, so I created an A record pointing to the IP address and a CNAME alias record to allow for www.xyz.co. The domain is sitting with godaddy and the name servers are configured to the AWS delegation set.

The instance itself sits in the default VPC. I double-checked and DNS resolution and DNS host names are both active.

I'm a bit stuck here with this. Any help would be highly appreciated!

Cheers, Bruno

Answer 1

What you are seeing isn't actually related to name resolution.

It's impossible for DNS to change what appears in the address bar of the web browser -- DNS and web browsers simply do not interact in a way that makes such behavior possible. Your URL is not "getting resolved to" this new value via anything DNS-related, since DNS, configured correctly or incorrectly, can't impact what shows up there, on its own.

The fact that navigating to the IP address has the same impact backs up this assertion.

What you are seeing is not related in any way to DNS or Route 53 or even EC2 or VPC. Your web server is, for whatever reason, configured to redirect incoming requests with any other hostname... over to the hostname you are subsequently seeing in the address bar (which is the one you don't like).

You should notice this in your web server's log. It will be issuing a 301 or 302 redirect on the initial request.

You should also be able to verify this yourself with the curl command line utility. Here, a server accessed as "www.example.com" is redirecting the browser to use its preferred address, "example.com." (Hostnames and addresses are sanitized, but the output is otherwise unmodified.)

$ curl -v www.example.com
* Rebuilt URL to: www.example.com/
* Hostname was NOT found in DNS cache
*   Trying 203.0.113.139...
* Connected to www.example.com (203.0.113.139) port 80 (#0)

The next block of output is the request sent to the web server.

> GET / HTTP/1.1
> User-Agent: curl/7.35.0
> Host: www.example.com
> Accept: */*
>

The http response from the web server includes a redirect.

< HTTP/1.1 301 Moved Permanently
< Content-length: 0
< Location: http://example.com/
< Connection: close
<
* Closing connection 0

If we were using a browser instead of a command line tool, this would cause the address bar to change to the new value, and establish a new connection to the web server (which might actually be the same one, or a different one... in this case, it's the same).

In spite of the fact that I had typed http://www.example.com into my browser, it would now show only http://example.com/. The same thing would happen if I typed in the IP address if my server was configured to redirect everything to one hostname, as yours appears to be. In my case, it's deliberately configured to do something else.

The above should illustrate that you do not actually have a DNS issue, and explain the mechanism that's causing this to occur (because you may find this to be something useful to do deliberately in the future, as my web servers do -- any www.* request gets stripped and rewritten without the www).

The issue is with your web server, telling the browser to use a different hostname. How to fix that will depend on what web server you are running and why it thinks the redirect is necessary.