Monday 21 July 2008

Perhaps extra keys on a keyboard aren't that bad an idea...

on the newfound use of useless keys

Whilst my work is nowadays mostly done on my macbook (running windows, much to my lament), at home I usually drop the laptop besides my desktop, boot it into mac os x, and use it as a communications central with email and IM open while working on some other thing on the desktop. Call it a strange dual-head, quad-core computing station.

Instead of switching around keyboards when I need to pass from one computer to the other, I use (and profoundly adore) synergy, which allows one keyboard+mouse combo to control more than one computer, via the network. But until now, to change from one computer to another (let's say to talk to someone on IM) my hand had to leave the home keys of the keyboard to use the mouse to move from one computer to the other (since synergy uses the edges of the monitor to cross control from one computer to another).

But no more! Remembering some button with "hotkeys" on the label on the configuration manager, I managed to bind two keys, one to move left, other to move right. But then the dilema... which keys?

I didn't want a hard, multiple key, emacs-like, binding. I was looking for a short stroke to allow for quick back-and-forth, since that was the most common scenario (coding on the desktop, and going to the laptop to spout nonsense on im and back again to serious business).

Enter the most useless keys on my current keyboard, a logitech internet navigator. A fine keyboard all in all, with a wheel on the left side (which I tend to use quite often, as a matter of fact) and two keys below it, go and back.

Previously useless keys

Bind go for left, back to right and we've got a pan-computer Alt-Tab.


Saturday 5 July 2008

Using capistrano to deploy a python application

At weListen we have a small python web application that we use as a time tracker and status keeper. Something akin to twitter, but with less social and more tracking. It lives in a Linux server together with a couple of our other services, and tends to be something I work on from time to time to improve small details or to fix small bugs.

Now, most of the time the development of this app is rather iterative. I think up of something new to try or a small improvement, code it on my local workstation, test it with live data taken from the production environment and if I'm happy with the results, I commit the change and deploy it on the production server. It's a small app, with a couple of services running, so the upgrade protocol is direct. It is still a couple of steps, and sometimes I tend to forget one of them (usually the one where I refresh the source code from subversion).

So, that looks like a good excuse to try out capistrano, of which I've heard many things, mostly coming from the ruby on rails community.

In a nutshell, what I wanted was for a library to take care of the connection and execution of commands on remote servers with minimal fuss. And that's what I got.

The Good

After installing the one click version, ruby was setup and ready to go. The gems library was already included, and installing capistrano was a matter of invoking the stanza featured on the project's home page.

Creating a script to perform the same steps I previously did manually was straightforward enough, and rather "obvious", apart from the trick to get sudo not to complain:

task :update, :hosts => "<server>" do
  default_run_options[:pty] = true # required so that sudo doesn't complain
  run "svn update ~/<directory>"
  sudo "/etc/init.d/<service 1> restart"
  sudo "/etc/init.d/<service 2> restart"

The server can use the standard username@host:post format, and the ssh framework plays nice with pageant, making passwordless logins updates real easy.

The Bad

No documentation, apart from a getting started tutorial, which is completely geared to deploying ruby on rails applications according to their methodology. Both seem to be a known problem, as a quick Google search for "capistrano documentation" gives us some pages with a call for help, and a mailing list post for it, and the getting started page warns us about it being devoted to ruby on rails.

Still, It leaves the rest of the world in the dark about how to use cap to deploy other kind of applications. Also, there isn't much in the way of explaining what is their methodology, and how can a user skip or customize some of the steps.  I ended up just running the commands with no automatic error checking. Which works for now, but leaves me a bit unsure as to how solid it is.

The Ugly

Since I use a private/public key combo to login to the server with a non-root user (standard Linux sysadmin practice), and sudo requires a password by default, the script didn't work out as well as I wanted it to be on the first try. I could either type the password each time I wanted to deploy the app, get ssh to pass through my private key from pageant to sudo, or tell sudo that the services don't require a password.

I ended up compromising and going with the last choice. It means that an attacker which gains access to the server via the normal user can restart the services and do a bit of damage, but if he's already inside, then a couple of services going down is the least of my worries.


If I already had ruby installed, adding capistrano to the list of dependencies is not a big deal. The library is small and easy to install using gems. The problem was simple, and with the right tools the solution was equally direct. The lack of documentation wasn't that big a deal, but mostly because the problem was small.

Sadly, capistrano is the only reason for me to have ruby installed, so far, making the dependency a large and difficult one to explain. I might have a look in the future for python based alternatives.

Also, I'm starting to wonder if I could use the idea behind capistrano to deploy windows based applications. The biggest problem would be the remote connection, but I believe that Windows Server 2008 already has some support for console based remote connections. If this were possible, deployments could be more easily automated, which would most likely reduce the overhead of getting a new version of a web based application live.