pov-fabric-helpers 0.1

Usage

For now add this repository as a git submodule

cd ~/src/project
git submodule add https://github.com/ProgrammersOfVilnius/pov-fabric-helpers
git submodule init

and in your fabfile.py add

sys.path.insert(0, os.path.join(os.path.dirname(__file__), 'pov-fabric-helpers'))
from pov_fabric import ...

Then remind your users to run git submodule init after they clone the repo with the fabfile.

Instance management

All of my fabfiles can manage several instances of a particular service. Externally this looks like

fab instance1 task1 task2 instance2 task3

which executes Fabric tasks task1 and task2 on instance instance1 and then executes task3 on instance2.

An instance defines various parameters, such as

• what server hosts it

• where on the filesystem it lives

• what Unix user IDs are used

• what database is used for this instance

• etc.

To facilitate this pov_fabric provides three things:

1. An Instance class that should be subclassed to provide your own instances

   from pov_fabric import Instance as BaseInstance
   
   class Instance(BaseInstance):
       def __init__(self, name, host, home='/opt/sentry', user='sentry',
                    dbname='sentry'):
           super(Instance, self).Instance.__init__(name, host)
           self.home = home
           self.user = user
           self.dbname = dbname

   and since that’s a bit repetitive there’s a helper

   from pov_fabric import Instance as BaseInstance
   
   Instance = BaseInstance.with_params(
       home='/opt/sentry',
       user='sentry',
       dbname='sentry',
   )

   which is equivalent to the original manual subclassing.

2. Instance.define() that defines new instances and creates tasks for selecting them

   Instance.define(
       name='testing',
       host='root@vagrantbox',
   )
   Instance.define(
       name='production',
       host='server1.pov.lt',
   )
   Instance.define(
       name='staging',
       host='server1.pov.lt',
       home='/opt/sentry-staging',
       user='sentry-staging',
       dbname='sentry-staging',
   )

3. A get_instance() method that returns the currently selected instance (or aborts with an error if the user didn’t select one)

   from pov_fabric import get_instance
   
   @task
   def look_around():
       instance = get_instance()
       with settings(host_string=instance.host):
           run('hostname')

Previously I used a slightly different command style

fab task1:instance1 task2:instance1 task3:instance2

and this can still be supported if you write your tasks like this

@task
def look_around(instance=None):
    instance = get_instance(instance)
    with settings(host_string=instance.host):
        run('hostname')

Be careful if you mix styles, e.g.

fab instance1 task1 task2:instance2 task3

will run task1 and task3 on instance1 and it will run task2 on instance2.

Testing Fabfiles with Vagrant

I don’t know about you, but I was never able to write a fabfile.py that worked on the first try. Vagrant was very useful for testing fabfiles without destroying real servers in the process. Here’s how:

• Create a Vagrantfile somewhere with

  Vagrant.configure("2") do |config|
    config.vm.box = "precise64"  # Ubuntu 12.04
    config.vm.box_url = "http://files.vagrantup.com/precise64.box"
    config.vm.provider :virtualbox do |vb|
      vb.customize ["modifyvm", :id, "--memory", "1024"]
    end
  end

• Run vagrant up

• Run vagrant ssh-config and copy the snippet to your ~/.ssh/config, but change the name to vagrantbox, e.g.

  Host vagrantbox
    HostName 127.0.0.1
    User vagrant
    Port 2222
    UserKnownHostsFile /dev/null
    StrictHostKeyChecking no
    PasswordAuthentication no
    IdentityFile /home/mg/.vagrant.d/insecure_private_key
    IdentitiesOnly yes
    LogLevel FATAL

• Test that ssh vagrantbox works

• In your fabfile.py create a testing instance

  Instance.define(
      name='testing',
      host='vagrant@vagrantbox',
      ...
  )

• Test with fab testing install etc.