Continuous Deployment with whiskey_disk

Continuous deployment rocks. Whiskey_disk makes it super easy. Here's how to set it up on your servers.

Step 1: Install whiskey_disk on your deployment machine

gem install whiskey_disk

Make sure to take note of your gem install location, as we'll need to be explicit about the location of the wd binary for the cron task in the next step. Hint: If you're using rvm on your deployment machine, it probably won't be /usr/local/bin/wd. Whatever the install location, knowing the exact install path is important because Cron runs with an extremely minimal envionment setup, so it's best to assume that your $PATH variable is not set at all.

The easiest way to do this is simply to run which wd, and use this in the cron task in the next step (the crontab below assumes the which wd output is /usr/local/bin/wd).

Step 2: Set up a cron task

When logged in as the user who performs the deploys, edit that user's crontab:

crontab -e

# Run every minute
* * * * * /usr/local/bin/wd --check --only=myapp.com --path=/var/www/shared/config/deploy.yml deploy

Let's walk through what's going on in the crontab.

The first part (prior to /usr/local/bin/wd) is the cron interval specification. I won't attempt to explain in entirety cron's archaeic interval specification format here, but plenty of documentation exists on this topic. The relevant part for our purposes is the first *, which indicates to cron, "run this every minute". If you wanted to run this say, every five minutes, simply change this to */5.

The --check flag tells whiskey_disk to check if HEAD in the remote repository is different from the local HEAD. If it is, whiskey_disk runs a deploy, per the instructions defined in the deploy.yml config file. Otherwise it does nothing.

The --only flag is how you tell wd to do a "local" deploy to the specified domain. "Local" means that wd won't attempt to ssh into the specified domain -- it will execute the deployment on the local filesystem. Note: The --only flag is also useful if you have multiple domains specified for a single deployment target (i.e. you're deploying to multiple servers) and you only want to deploy to one of them.

The --path flag is the path to the application's deploy.yml file.

Step 3: git push!!

Now, all you have to do is push to the remote specified in your deploy.yml, and whiskey will check every minute and deploy if anything has changed. That's it. Seriously. Happy hacking!