# Deploying with Fabric & Mercurial

Posted on January 15, 2009.

Earlier tonight I added support for the Mint Bird Feeder plugin to my site’s RSS feeds. Bird Feeder isn’t designed to work with Django so I had to change a few things to get it up and running. I mostly followed the instructions on Hicks-Wright.net with a few tweaks.

While I was trying to get things running smoothly I had to redeploy the site a bunch of times so I could test the changes I made. If I were simply FTP’ing the files over each time I wanted to redeploy it would have been a huge pain. Fortunately, I have another way to do it that cuts down on my typing.

## My Basic Deployment Steps

The code for my site is stored in a Mercurial repository. There are actually three copies of the repository that I use:

• One is on my local machine, which I commit to as I make changes.
• One is on BitBucket, which I use to share the code with the public.
• One is on my host’s webserver, and is what actually gets served as the website.

When I’m ready to deploy a new version of the site, I push the changes I’ve made on my local repository to the one on BitBucket, then pull the changes from BitBucket down to the server. Using push/pull means I don’t have to worry about transferring the files myself. Using BitBucket in the middle (instead of going right from my local machine to the server) means I don’t have to worry about serving either repository myself and dealing with port forwarding or security issues.

## Putting BitBucket in the Middle

Using BitBucket as an intermediate repository is actually fairly simple. Here are the basic steps I use to get a project up and running like this.

First, create a new repository on BitBucket. Make sure the name is what you want. Feel free to make it private if you just want it for this, or public if you want to go open source.

### Set Up Your Local Machine

Clone this new, empty repository to your local machine. If you already have code written you’ll need to copy it into this folder after cloning. I don’t know if there’s a way to push a brand-new repository to BitBucket; if you know how please tell me.

On your local machine, edit the .hg/hgrc file in the repository and change the default path to:

default = ssh://hg@bitbucket.org/username/repositoryname/


That will let you push/pull to and from BitBucket over SSH. Doing it that way means you can use public/private key authentication and avoid typing your password every single time. A fairly comprehensive guide to that can be found here. You can ignore the server-side configuration; you just need to add your public key on BitBucket’s account settings page and you should be set.

UPDATE: I didn’t realize it before, but BitBucket has a guide to using SSH with BitBucket. It’s definitely worth looking at.

Now you should be able to use hg push and hg pull on your local machine to push and pull changes to and from the BitBucket repository. The next step is getting it set up on the server side.

On your server, use hg clone to clone the BitBucket repository to wherever you want to serve it from. Edit the .hg/hgrc file in that one and change the default path to the same value as before:

default = ssh://hg@bitbucket.org/username/repositoryname/


Once again, set up public/private key authentication; this time between the server and BitBucket. You can either copy your public and private keys from your local machine to the server (if you trust/own it) or you can create a new pair and add its public key to your BitBucket account as well.

While you’re at it, set up public/private key authentication to go from your local machine to your server too. It’ll pay off in the long run.

Now that you’ve got both sides working, you can develop and deploy like so:

• Make changes on your local machine, committing as you go.
• Push the changes to BitBucket.
• SSH into your server and pull the changes down.
• Restart the web server process if necessary.

Not too bad! Instead of manually managing file transfers you can let Mercurial do it for you. It’ll only pull down the files that have changed, and will always put them in exactly the right spot. That’s pretty convenient, but we can do better.

## Weaving it All Together with Fabric

Being able to push and pull is all well and good, but that’s still a lot of typing. You need to enter a command to push your changes, a command to SSH to the server, a command to change to the deploy directory, a command to pull the changes, and a command to restart the server process. That’s five commands, which is four commands too many for me.

To automate the process, I use the wonderful Fabric tool. If you haven’t seen it before you should take a look. To follow along with the rest of the section you should read the examples on the site and install Fabric on your local machine.

### My Current Setup

Here’s the fabfile I use for deploying my site to my host (WebFaction). It’s pretty specific to my needs but I’m sure it will give you an idea of where to start.

def prod():
"""Set the target to production."""
set(fab_hosts=['sjl.webfactional.com'])
set(fab_key_filename='/Users/sjl/.ssh/stevelosh')
set(remote_app_dir='~/webapps/stevelosh/stevelosh')
set(remote_apache_dir='~/webapps/stevelosh/apache2')

def deploy():
"""Deploy the site."""
require('fab_hosts', provided_by = [prod,])
local("hg push")
run("cd $(remote_app_dir); hg pull; hg update") run("cd$(remote_app_dir); python2.5 manage.py syncdb")
run("$(remote_apache_dir)/bin/stop; sleep 1;$(remote_apache_dir)/bin/start")

def debugon():
"""Turn debug mode on for the production server."""
require('fab_hosts', provided_by = [prod,])
run("cd $(remote_app_dir); sed -i -e 's/DEBUG = .*/DEBUG = True/' deploy.py") run("$(remote_apache_dir)/bin/stop; sleep 1; $(remote_apache_dir)/bin/start") def debugoff(): """Turn debug mode off for the production server.""" require('fab_hosts', provided_by = [prod,]) run("cd$(remote_app_dir); sed -i -e 's/DEBUG = .*/DEBUG = False/' deploy.py")
run("$(remote_apache_dir)/bin/stop; sleep 1;$(remote_apache_dir)/bin/start")


When I’m finished committing to my local repository and I want to deploy the site, I just use the command fab prod deploy on my local machine. Fabric pushes my local repository to BitBucket, logs into the server (with my public key—no typing in passwords), pulls down the new changes from BitBucket and restarts the server process.

I also set up a couple of debug commands so I can type fab prod debugon and fab prod debugoff to change the settings.DEBUG option of my Django app. Sometimes it’s useful to turn on debug to find out exactly why a page is breaking on the server.

### Extending It

The reason I split off the prod command is so I can set up a separate test app (on the server) in the future and reuse the deploy and debug commands. All I’d need to do is add a test command, which might look something like this:

def test():
"""Set the target to test."""
set(fab_hosts=['sjl.webfactional.com'])
set(fab_key_filename='/Users/sjl/.ssh/stevelosh')
set(remote_app_dir = '~/webapps/stevelosh-test/stevelosh')
set(remote_apache_dir = '~/webapps/stevelosh-test/apache2')


Deploying the test site would then be a simple fab test deploy command.

## Why Should You Try This?

After you’ve gotten all of this set up the first time it will start saving you time every time you deploy. It also prevents stupid mistakes like FTP’ing your files to the wrong directory on the server. It frees you from those headaches and lets you concentrate on the real work to be done instead of the busywork. Plus setting it up again for a second project is a breeze after you’ve done it once.

Obviously the exact details of this won’t be a perfect fit for everyone. Maybe you prefer using git and GitHub for version control. I’m sure there’s a similar way to automate the process on that side of the fence. If you decide to write something about the details of that please let me know and I’ll link it here.

My hope is that this will at least give you some ideas about saving yourself some time. If that helps you create better websites, I’ll be happy. Please feel free to find me on Twitter with any questions or thoughts you have!

## Update

It’s been over a year since I originally wrote this entry and I’ve learned quite a bit since then. I don’t have the time right now to go back and rewrite the entire article, but here are some of the main things that have changed:

• I now use virtualenv and pip when deploying Django sites. It sandboxes each site very nicely and makes it easy to deploy.

• I no longer go “through” BitBucket when deploying — I push directly from my local machine to the server. This eliminates an extra step, and I can always push to BitBucket once I’m done with a series of changes.

• Fabric is completely different. “Ownership/maintenance” of the project has transferred to a new person and the format of fabfiles has drastically changed.

Here’s a sample fabfile from one of the projects I’m working on now. There are no comments, but I think most things should be self-explanitory. If you have any questions just find me on Twitter and I’ll be glad to answer them.

from fabric.api import *

REMOTE_HG_PATH = '/home/sjl/bin/hg'

def prod():
"""Set the target to production."""
env.hosts = ['sjl.webfactional.com']
env.remote_app_dir = 'webapps/SAMPLE/SAMPLE'
env.remote_apache_dir = '~/webapps/SAMPLE/apache2'
env.local_settings_file = 'local_settings-prod.py'
env.remote_push_dest = 'ssh://webf/%s' % env.remote_app_dir
env.tag = 'production'
env.venv_name = 'SAMPLE_prod'

def test():
"""Set the target to test."""
env.hosts = ['sjl.webfactional.com']
env.remote_app_dir = 'webapps/SAMPLE_test/lindyhub'
env.remote_apache_dir = '~/webapps/SAMPLE_test/apache2'
env.local_settings_file = 'local_settings-test.py'
env.remote_push_dest = 'ssh://webf/%s' % env.remote_app_dir
env.tag = 'test'
env.venv_name = 'SAMPLE_test'

def deploy():
"""Deploy the site.

This will also add a local Mercurial tag with the name of the environment
(test or production) to your the local repository, and then sync it to
the remote repo as well.

This is nice because you can easily see which changeset is currently
deployed to a particular environment in 'hg glog'.
"""
require('hosts', provided_by=[prod, test])
require('remote_app_dir', provided_by=[prod, test])
require('remote_apache_dir', provided_by=[prod, test])
require('local_settings_file', provided_by=[prod, test])
require('remote_push_dest', provided_by=[prod, test])
require('tag', provided_by=[prod, test])
require('venv_name', provided_by=[prod, test])

local("hg tag --local --force %s" % env.tag)
local("hg push %s --remotecmd %s" % (env.remote_push_dest, REMOTE_HG_PATH))
put(".hg/localtags", "%s/.hg/localtags" % env.remote_app_dir)
run("cd %s; hg update -C %s" % (env.remote_app_dir, env.tag))
put("%s" % env.local_settings_file, "%s/local_settings.py" % env.remote_app_dir)

run("workon %s; cd %s; python manage.py syncdb" % (env.venv_name, env.remote_app_dir))
restart()

def restart():
"""Restart apache on the server."""
require('hosts', provided_by=[prod, test])
require('remote_apache_dir', provided_by=[prod, test])

run("%s/bin/stop; sleep 2; %s/bin/start" % (env.remote_apache_dir, env.remote_apache_dir))

def debugon():
"""Turn debug mode on for the server."""
require('hosts', provided_by=[prod, test])
require('remote_app_dir', provided_by=[prod, test])
require('remote_apache_dir', provided_by=[prod, test])

run("cd %s; sed -i -e 's/DEBUG = .*/DEBUG = True/' local_settings.py" % env.remote_app_dir)
restart()

def debugoff():
"""Turn debug mode off for the server."""
require('hosts', provided_by=[prod, test])
require('remote_app_dir', provided_by=[prod, test])
require('remote_apache_dir', provided_by=[prod, test])

run("cd %s; sed -i -e 's/DEBUG = .*/DEBUG = False/' local_settings.py" % env.remote_app_dir)
restart()