Here is a small example of how to write a typical deploy script with Python Fabric:

First, define your various servers which you need to deploy to. Ideally, you’ll have a test, staging and live server. Thus you’ll set them up as follows.

def test():
    config.fab_user = 'test_user_name'
    config.fab_hosts = ['test.yourserver.com']

def staging():
    config.fab_user = 'staging_user_name'
    config.fab_hosts = ['staging.yourserver.com']

def live():
    config.fab_user = 'live_user_name'
    config.fab_hosts = ['www1.yourserver.com', \
'www2.yourserver.com', 'www3.yourserver.com']

This allows you to deploy your code to the various servers. Please note, you need to setup automatic login for your different servers. See here how to do automatic logins.

Next, write the steps you would take to deploy your site manually:

def deploy():
    "Deploy code to servers"
    msg = "deploying"
    require('fab_hosts', provided_by = [test,staging,live])
    local('svn ci -m "$(msg)"')
    run('svn export repos /path/to/repository/export/')
    run('cp -R /path/to/repository/export/* /path/to/your/site/')

To deploy to the staging server you can run the following command:

$ fab staging let:msg="Reason for check in" deploy

To deploy to the 3 live servers, all you do is:

$ fab live let:msg="Reason for check in" deploy

The command works as follows: fab is the command. live/stating/test are the environments you would like to load. If you said staging, it will do the commands in deploy for the staging server. The last part is the command you want to run. In this instance, deploy.

The let:msg=”Reason for check in” is the coolest bit! It basically allow you to override Fabric variables. If you look closely, in my deploy script I’ve set a variable msg to just say “deploy”. Now that is a stupid SVN message for a commit. In order to commit with meaningful messages, I override the msg variable with my own message. Simple, yet very effective!

You may want to write a number of different functions in a single fabfile. If you have 100 commands and you’re not one hundred percent sure, just do a:

$ fab list

and all the commands available to you will be printed with their description. Fabric rocks! Seriously.

In all fairness, its not that I believe it is crap, its just that there is so much better ways to update sites. My preference at the moment is:

• Subversion
• Capistrano or Python Fabric
• or SSH and SCP if you don’t want to or cannot use the above

I do understand that if you host sites on a shared host you don’t always have these options and in lots of instances FTP is the only option available to you. I feel your pain :(

Today I came across Fabric, which is a Python version of Capistrano. Now, for the record, my use of Capistrano has been limited. I use it for what I need it. Nothing more. What I’m trying to say is I didn’t go into a very advanced setup of Capistrano, so I’m not really qualified to say which is better. On the Fabric page it says:

It is a bit like a dumbed down Capistrano, except it’s in Python

I like it. Its simple and it is easier than Capistrano IMHO. In the end, it comes down to which tool suits you best! Capistrano does support commits and rollbacks which, by the looks of it, Fabric don’t.

Setting up Capistrano was painless. All I had to do was

sudo gem install capistrano

Fabric had a few dependency issues, which I had to meet first before I could

sudo easy_install Fabric

It was looking for pycrypto which I had to install before I could setup Fabric.

Once installed, using it is as straight forward as Capistrano. All you need to do is to create a fabfile which is a simple python file which holds all the config options and commands to execute remotely. The syntax is plain and simple and clean. Here is a simple example executing a directory listing on a remote server:

def listing():
    "Outputs a directory listing on the remote server."
    set(fab_user = 'stii')
    set(fab_hosts = ['stii.co.za'])
    run('ls -l /usr/bin')

Simple. Apart from the run command to execute remote queries, there are also a sudo (execute remote commands as a privileged user), local (execute commands on your local machine) and put (upload files to the remote servers) which is very handy.

I’m going to use it a bit more and would give you more feedback in a while. If you want, you can check it out!

Update: Here is an example of how to upgrade WordPress using Python Fabric