Iis – Redirect to another web server if current page is down

The simple question to ask here is;

What IP is returned when you ping mydomain.com or www.mydomain.com?

Is it the correct address?

If not, then you've either cached a response, have not reloaded the zone or have not edited correctly.

I'd assume the response should now be a public IP rather than a private.

You should also query the DNS server directly as opposed to 'pinging';

dig @dns_server_ip mydomain.com A

Just to let you know, there are records, and they are propagating. Firstly the domain registration and delegation of the nameservers is OK:

[madhatta@www ~]$ whois alexchen.co @whois.nic.co
[Querying whois.nic.co]
[whois.nic.co]
Domain Name:                                 ALEXCHEN.CO
[...]
Name Server:                                 NS1.DREAMHOST.COM
Name Server:                                 NS2.DREAMHOST.COM
Name Server:                                 NS3.DREAMHOST.COM

Secondly, at least one nameserver at dreamhost is serving an A record for you:

[madhatta@www ~]$ dig alexchen.co @ns1.dreamhost.com
[...]
;; ANSWER SECTION:
alexchen.co.        14400   IN  A   173.236.220.66

So that much is working. It seems to me that if you put up the alexchen.co site on 173.236.220.66, and the webserver there is configured to serve it, everything should work. I must also add that, when I point a web browser at alexchen.co, I see nice, shiny wordpress site looking back at me. What do you see?

What interests me is that your old domain is on a different address:

[madhatta@kiev systems]$ dig alexchen.info
[...]
;; ANSWER SECTION:
alexchen.info.      14400   IN  A   173.236.217.156

I don't know the details of what you're trying to do, but is that what you expected? If so, can you confirm that you're still having the problems, and they weren't - as others have sensibly suggested - propagation delays?

You say you're on ubuntu, which should have both the tools I've used above, dig and whois; they're invaluable for trying to debug DNS issues.