I’ve been using account_location for a couple of applications recently. It’s a really nice way to give individual ‘clients’ of an application their own domain and when we come to scaling up, it’s a really easy way of splitting customers across several hosts. So, yeah, very nice. And it’s dead easy to deploy in the first instance – a couple of DNS records along the lines of:

@ IN A
* IN A

There you go, every host in that domain points to

However, it’s a pest for setting up in your development environment. OK, so you can edit /etc/hosts and add an entry for every single account you happen to create. This hinders development for me – each domain has to be unique, so whenever I want to create a new account, I have to do so in Rails, and in /etc/hosts. It’s also irritating when I’m having to maintain an /etc/hosts file on multiple machines. Unfortunately, the hosts file doesn’t support wildcard records, so we have to put every single entry in.

I’m sure there’s a better solution on Mac OS X – maybe there’s something smart I could do with the NetInfo database, or maybe I could play with Bonjour in some way – but the easiest thing for me was to set up a name server on my local machine. It’s really dead simple. Handily enough, BIND is already installed in the base system, just not configured and switched on. So we just have to do a little configuration. First of all, create the rndc configuration to control the name server:

mathie@bowmore:mathie$ sudo -s
bowmore:/Users/mathie root# rndc-confgen > /etc/rndc.conf
bowmore:/Users/mathie root# head -n5 /etc/rndc.conf |tail -n4 > /etc/rndc.key

This creates a key in /etc/rndc.conf which allows the rndc client to talk to the name server and control it. We then need to tweak the server configuration a little. In the controls section, change the port from 54 to 953 (I don’t know why it’s different by default, since it doesn’t seem to work!). Next up we need to create a stanza in /etc/named.conf for the Rails application zone. Add something along the lines of:

zone "rails" IN {
        type master;
        file "rails.zone";
        allow-update { none; };

around the other zone stanzas. Save that and move on. Next thing is to create /var/named/rails.zone. I started by copying the default localhost.zone, winding up with something along the lines of:

$TTL    86400
$ORIGIN rails.
@                       1D IN SOA       @ root (
                                        42              ; serial (d. adams)
                                        3H              ; refresh
                                        15M             ; retry
                                        1W              ; expiry
                                        1D )            ; minimum

                        1D IN NS        @
                        1D IN A

*.app1 IN A
*.app2 IN A

Save that and quit. Finally, we need to convince BIND to start up at boot. Since I’m on Tiger, we have the benefit of launchd to handle such mundane tasks. Simply run:

mathie@bowmore:mathie$ sudo launchctl load -w /System/Library/LaunchDaemons/org.isc.named.plist

BIND will start now, and will automatically start from now on at launch. if you’re on anything older, I gather it’s a case of adding:


to /etc/hostconfig. You can then restart your computer for it to take effect (it would be a good idea to verify it works) or cheat and run:

sudo /usr/sbin/named

to start it for now.

Finally, you need to tell your computer to use the newly setup name server. In System Preferences, go to the Network pane. For every one of the connections you use, in every one of the locations you have set up, go to the TCP/IP settings and add as the first DNS server.

Now every time you do a lookup for foo.app1.rails, bar.app2.rails or, well, anything at either domain, it will resolve to So you can happily browse to http://rubaidh.app1.rails:3000/ and account_subdomain will be set to ‘rubaidh’. Neat, huh?

A Sneak Peek at
The Internet

If you enjoyed this article, you might be interested in my new project, A Sneak Peek at The Internet. What happens when you enter www.facebook.com into your web browser and hit return? A Sneak Peek at The Internet will take you on a deep dive through the network stack, from HTTP, SSL, TCP and IP, all the way down through the data link layer, back up to Facebook's data centres, and then on the return journey back to the browser.

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