Ever done a site migration and not been sure which server you were seeing in the browser? Here are a few steps you can do to verify:
We’ll assume you’re changing the site at example.com is currently at 10.0.0.10 and you’re moving it to 172.16.0.11. First let’s check that the DNS changes you made are available:
$ nslookup example.com
should return something like:
server: 22.214.171.124 Address: 126.96.36.199#53 Non-authoritative answer: Name: example.com Address: 172.16.0.11
So here we see the new IP address. But we’re still seeing the old address in the browser. Well, let’s clear the OS level DNS cache:
For Linux - it depends. Many systems don’t cache DNS records. Others do so via
ncsd. You’ll need to check your distribution / installation to find the correct way.
So now we’ve changed the DNS successfully, flushed our OS level cache (or we aren’t using a cache). Surely the new site will show up now. Wait… what?? It doesn’t?!? What could be going on? Oh… the browser. Let’s clear the browser cache. Still no?
Well, if you’re using Chrome, try going to
chrome://net-internals/#dns and hitting the
Clear host cache button.
If you’re using Firefox put
about:config in the address bar and hit enter. In the search bar type
network.dns and the entries will be filtered down. Find the entry that says
network.dnsCacheExpiration and make note of the value (3600). Change the value to 0. Now go back and change it to the original value.
As far as I can tell, Safari uses the OS level DNS cache. I haven’t used Opera or IE for a while so I don’t know about those.