1. fabric
Control your linux nodes with python

2. What is it?
• Command-line tool for deployment automation and system
administration as a ssh wrapper
• Executes to local or remote
✓ local: not a ssh connection. uses python subprocess
module.
✓ run or sudo: when executing against remote, it can
execute as the current user or as current user with
sudo rights.

3. What is it?
• Simply specify python functions in fabfile.py
• Install it
✓ pip install fabric
✓ Once installed, fab command is available in your system
path.
✓ Start writing your python function in fabfile.py

4. automation
• Daily tasks
• Server setup
• System update and maintenance
• New project creation
• Deployment processes

5. get started
• Download and install virtualbox https://www.virtualbox.org
• Download and install vagrant http://www.vagrantup.com
cd ~/VirtualBoxVMs
mkdir debsqueeze64
cd debsqueeze64
vagrant init debsqueeze64 http://www.emken.biz/vagrant-
boxes/debsqueeze64.box
vagrant up

6. get started
• This downloads and creates an image of debian 64-bit on
your computer.
• We will use fabric on our local machine to interact with
this debian virtual machine
• See http://www.vagrantbox.es to download other prepared
boxes.

7. PythonVirtualenv
• Create an isolated python project environment
Mac OS X: package management with port or brew
sudo port -v install virtualenv_select py27-virtualenv
sudo port -v install py27-virtualenvwrapper
sudo port select --set virtualenv virtualenv27
(optional)

8. PythonVirtualenv
• Edit your ~/.bash_profile
export WORKON_HOME=$HOME/.virtualenvs
export PROJECT_HOME=$HOME/work
source `which virtualenvwrapper.sh`
• $HOME -- this refers to your user home or “~”
(i.e., on my computer,“~” means “/Users/calvin” directory)
(optional)

9. PythonVirtualenv
• Create our python virtualenv for our fabric tutorial
mkvirtualenv --distribute --no-site-packages learnfabric
cd $PROJECT_HOME
git clone git://github.com/calvinchengx/learnfabric.git
cd learnfabric
pip install -r requirements.txt
(optional)

10. learn fabric
• Once we have our debian virtual machine and optionally
our python virtualenv ready, we begin
git clone git://github.com/calvinchengx/learnfabric.git
cd learnfabric
pip install -r requirements.txt
cp -rf ~/VirtualBoxVMs/debsqueeze64/.vagrant .
• This installs fabric and installs python-vagrant (a wrapper
around vagrant commands so we can programmatically
control our vagrant instance)

11. learn fabric
• Once we have our debian virtual machine and optionally
our python virtualenv ready, we begin
git clone git://github.com/calvinchengx/learnfabric.git
cd learnfabric
pip install -r requirements.txt
cp -rf ~/VirtualBoxVMs/debsqueeze64/.vagrant .
• This installs fabric and installs python-vagrant (a wrapper
around vagrant commands so we can programmatically
control our vagrant instance)

12. fabric function
fab mytask
[vagrant@127.0.0.1:2222] Executing task 'mytask'
[vagrant@127.0.0.1:2222] run: echo $USER
[vagrant@127.0.0.1:2222] out: vagrant[vagrant@127.0
.0.1:2222] out:
Done.
Disconnecting from vagrant@127.0.0.1:2222... done.

13. the code
import vagrantfrom fabric.api import env, task, runv =
vagrant.Vagrant()v.up()env.hosts =
[v.user_hostname_port()]env.key_filename =
v.keyfile()env.disable_known_hosts = True # useful when vagrant box ip
changes.
# our first fabric function@taskdef mytask(): run('echo $USER')
@taskdef mytask(): run('echo $USER')

14. fabric core
• local() runs a command locally, via python subprocess
• run() runs a command remotely, via ssh
• sudo() runs a command remotely as sudo, via ssh
• put() copies a file from local to remote, via ssh
• get() copies a file from remote to local, via ssh

15. fabric AUth
• All authentication is ssh-based
• SSH keys help us avoid typing in passwords - place fabric
ssh user (env.user)’s public key in remote node’s
authorized_keys
• Avoid directly using root user
• Give your fabric ssh user sudo rights instead (env.user)

16. fabric config
• from fabric.api import env
• fabric environment is simply a dictionary containing host
information, roles, user (env.user); and
• any other custom information you would like to include.
• $HOME/.fabricrc allows custom configuration, e.g.
user = ssh_user_name
where “ssh_user_name” is any value you so desire to pass
in to env.user when a fab function runs.

17. Fabric ROLEDEFS
# code
from fabric.api import env
env.roledefs = {
‘web’: [‘100.0.0.1’, ‘100.0.0.2’],
‘db’: [‘100.0.0.3’],
‘media’: [‘100.0.0.4’]
}
# command line
fab -R web mytask

18. Fabric host(S)
# code
from fabric.api import env
env.roledefs = {
‘web’: [‘100.0.0.1’, ‘100.0.0.2’],
‘db’: [‘100.0.0.3’],
‘media’: [‘100.0.0.4’]
}
# command line
fab -H 100.0.0.1,100.0.0.2 mytask

19. map roles to tasks
# code
from fabric.api import env
from fabric.decorators import roles
env.roledefs = {
‘web’: [‘100.0.0.1’, ‘100.0.0.2’],
‘db’: [‘100.0.0.3’],
‘media’: [‘100.0.0.4’]
}
@roles(‘web’)
def mytask():
run(‘uptime’)
# command line
fab mytask # already mapped to -R web

20. handling failures
• Do not abort upon failure; just give a warning
# code
from fabric.context_managers import settings
def mytask():
with settings(warn_only=True):
run(‘rm /var/www/proj/releases/current’)
run(‘ln -s /var/www/proj/releases/deployed
/var/www/proj/releases/current’)

21. Lazy sysadmin
• A generic command
# code
@roles(‘all’)
def invoke(command):
“””
Invoke an arbitrary command
“””
sudo(command)
# command line
fab invoke:“aptitude update”
fab invoke:”aptitude upgrade”

22. parallel execution
• A generic command
# code
@roles(‘all’)
def invoke(command):
“””
Invoke an arbitrary command
“””
sudo(command)
# command line
fab -P invoke:“aptitude update”
fab -P invoke:”aptitude upgrade”

23. python web app

24. Example deploy
@task(default=True)@set_target_envdef deploy(email=False): """ `fab -R all deploy` or fab -H mysite.com deploy`.
Execute a deployment to the given groups of hosts or host """ if not chk_req(): return if git_branch_check()
or test_host_check(): manage_release('Deployment start') git_archive_and_upload_tar()
pip_requirements() collectstatic(deploy=True) symlink_current() webserver()
migrate_db() # post-deployment tasks manage_release('Deployment end') _releases_cleanup()
email_on_success(trigger=email)
# command line
fab -R all deploy

25. quick refErence
• fab -H host1.com task
• fab -H host1.com task:arg1,arg2
• fab -P -H localhost, host1.com, host2.com task
• fab -R web task # roles defined by env.roledefs
• fab -R web task:arg1,arg2
• fab -P -R web task
• fab -l
• more options explained via fab --help

26. devops
• Bridging the gap between code implementation by
developers and deployment to staging and/or live servers
by sysadmin
• Automation leads to continuous integration (e.g. Jenkins CI
Server) and continuous delivery
• Support heterogeneous development environment in
combination with vagrant (developers test against vagrant,
which has same distro as staging and production hosts)

27. referenceS
• My reusable fabric functions
https://github.com/fabric-colors/fabric-colors
https://fabric-colors.readthedocs.org/en/latest/index.html
• Code that accompanies this set of slides
https://github.com/calvinchengx/learnfabric
• Fabric code and documentation
https://github.com/fabric/fabric
http://fabric.readthedocs.org
• Multiple vagrant boxes for testing your server config
http://awaseroot.wordpress.com/2012/05/06/script-for-

28. q&A
• Get in touch @calvinchengx
• http://calvinx.com