Using etc/Hosts to Assist in Testing

A coworker and I were in the process of migrating a client’s web server from old hardware to new hardware last week, and we needed to be able to test the system before turning it on to live traffic. The web applications called web services, and the configuration of the web app included the URL for the web services.

We needed to be careful what we were doing here, because the web services were also migrating to a new server, and on this new server, were pointing to a new database server as well. We didn’t want to change all the configuration settings on the new servers, and we couldn’t change the public DNS entry.

I’ve done this before, but not everyone knows about the following trick, so here it is:

On Windows, if you go into your %WinDir%\System32\drivers\etc directory, you’ll find a file called hosts, often referred to as “etc\hosts” or “Etsy Hosts”. Open this file with notepad running as administrator on your machine. The instructions for changing this file are right in there, and it’s pretty easy. We added a new line to file on the new server, (and on the test client) like:

127.0.0.1       www.palador.com

We saved our changes, and then restarted IIS on the box. And presto…

But it didn’t work.

We reset IIS again, and did an ipconfig /flushdns from the command prompt.

And it still pointed to the old domain.

We went back to the Hosts file and everything looked fine. I scratched my head. Then I realized that we had forgotten to put a carriage return after the new line. We added the hard-return, restarted IIS and flushed DNS, and now everything worked.

I’m pretty sure I had run into this exact same issue a few years ago, and that’s why I knew to look for it. Hopefully this will help someone else avoid this issue.