In a previous post I described some of the initial magic that I use to automate this site. That initial magic is using virtual python environments through the use of virtualenv and virtualenvwrapper. See that post for more.

In this post, I’m gonna describe a more general purpose tool that allows automation through Python scripts across hosts, Fabric.

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Fabric

Fabric has got to be one of the greatest Python tools I’ve come across in a long time. I’ve written similar code that used an XML-RPC mechanism, but Fabric does it right. And I’m really glad I found it when I did. I was actually starting to work on something very similar from the ground up for my own usage.

What Fabric provides for me in the context of authoring this website is automated build and publishing capability. In the most general sense, Fabric provides a way to script administrative tasks on local and remote machine(s) using a local Python script.

It performs these actions using SSH, rsync, some UNIX shell utilities like sed, and even some Django integration for some backend automation. I’ve certainly seen most usage of Fabric used in conjunction with website management, but I’m working on some scripts that will provide some administrative functionality for managing routers and switches over SSH — things like pulling configs, running stats, and pushing quick fixes like a logging server change.

Example

So I’ll run through just the simple script that this site currently uses. The heart of any Fabric deployment is the fabfile.py. The command on your path that you use is fab. fab travels up the directory tree until it finds a fabfile that it can use. While I use a flat fabfile.py Python module, you can also use a fabfile/ directory containing an __init__.py file. Optionally, you can point fab to any other Python module.

So fab will import your fabfile and generate a list of tasks to perform. These tasks have certain properties that you can modify on the command line. One property is the hosts. Fabric will run each specified task on each host specified in env.hosts, which is a Python list of host strings. A host string contains a username and host definition (optionally a port number). An example is user@www.example.com or author@10.10.10.10:22.