DNS name and IP address do not resolve the same - amazon-ec2

Question

I have checked it at: http://www.ipchecking.com/ and they say they are the same. but when I visit each of them they are different
ec2-54-206-38-225.ap-southeast-2.compute.amazonaws.com - 404 error Problem accessing /. Reason: Not Found
54.206.38.225 - returns apache default page
ec2-54-206-38-225.ap-southeast-2.compute.amazonaws.com/jenkins - jenkins launchs
54.206.38.225/jenkins - not found
My understanding was that the host name should resolve to the ip address and thus they shouldboth take me to the same place?

Answer 1

What you are probably seeing is due to named based virtual hosts.
When your browser makes an HTTP request, it includes a header that says what host it is looking for. This allows a server to have more than 1 site hosted on a single IP address and port.
This can also allow a load balancer to redirect your traffic to different machines on its network for handling.
You can find more information at
https://en.wikipedia.org/wiki/Virtual_hosting
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

Answer 2

Check this:
# curl -I -s http://ec2-54-206-38-225.ap-southeast-2.compute.amazonaws.com | head -3
HTTP/1.1 404 Not Found
Date: Tue, 05 Jan 2016 06:15:49 GMT
Server: Jetty(winstone-2.9)
# curl -I -s http://54.206.38.225 | head -3
HTTP/1.1 200 OK
Date: Tue, 05 Jan 2016 06:16:00 GMT
Server: Apache/2.4.7 (Ubuntu)
# curl -I -s http://ec2-54-206-38-225.ap-southeast-2.compute.amazonaws.com/jenkins | head -3
HTTP/1.1 302 Found
Date: Tue, 05 Jan 2016 06:16:18 GMT
Server: Jetty(winstone-2.9)
# curl -I -s http://54.206.38.225/jenkins | head -3
HTTP/1.1 404 Not Found
Date: Tue, 05 Jan 2016 06:16:28 GMT
Server: Apache/2.4.7 (Ubuntu)
From above commands (look at the HTTP response code closely),
When FQDN is used, the HTTP request is responded by JeTTy.
When IP Address is used, the HTTP request is responded by Apache.
Jetty is aware of /jenkins path
Apache is not aware of /jenkins path.
So this implies that, You have JeTTy acting as Reverse_Proxy/Load_Balancer. So the connection looks like this:
USER --> JeTTy --> Apache
Now, you need to figure out how JeTTy is configured for redirecting/denying requests. This link might be helpful.
However, Usually, I have seen that an application server is fronted by a web server as Reverse_Proxy/Load_Balancer. So, you might find that your setup looks like below:
USER --> Apache --> JeTTy
If this is the case then figure out how Apache is configured for redirecting/denying requests.