[Fab-user] external role definitions

[Michael Gliwinski]

Hello fab(ulous) people!

I've been using Fabric for a while now but am new to the list.  I'm just 
catching up with archives and I've noticed that the question of loading roles 
from external sources sometimes pops up.

I have this class which I use in my fabfiles that I thought could be useful to 
some, and if it would, I can submit a patch to put it in contrib or even 
directly in fabric.state.

Basically, the class inherits from the builtin dict and behaves like a normal 
dictionary with additional option to load data from external source.  A list 
of sources can be passed to load_from method and the first available (i.e. 
first one which returns without raising exception) will be used.

A source can be a local path to file, a URL or a callable which should return 
a mapping of roles to host lists.

In my implementation data from file or URL is expected to be in YAML format, 
but since this would mean additional dependency I can change it to something 
else.

In any case the source_loader attribute can also be reassigned to a custom 
function that loads other formats.

For example, given a file 'roles.yml' with contents: 'foo: [bar, baz]\n':

  >>> r = RoleDefs()
  >>> r.load_from(['nonexistent.yml', 'roles.yml'])
  >>> r['foo']
  ['bar', 'baz']

The source is loaded "lazily" - only when the first missing key is accessed 
which means an instance of RoleDefs can be assigned to env.roledefs without 
causing delay on every fab invocation.

My usecase for this is that I usually export the roles (or access them 
directly) from Spacewalk/Cobbler, but sometimes e.g. when I'm working over VPN 
I have to connect through SSH tunnels (port redirs) through a gateway, so I 
have a local file with some roles redefined in terms of those redirections.

Anyways, if you're interested I can do something about getting that into 
Fabric.  Let me know sure.

Thanks for the great work!

Michael


-- 
Michael Gliwinski
Henderson Group Information Services
9-11 Hightown Avenue, Newtownabby, BT36 4RT
Phone: 028 9034 3319

-- 
Michael Gliwinski
Henderson Group Information Services
9-11 Hightown Avenue, Newtownabby, BT36 4RT
Phone: 028 9034 3319

**********************************************************************************************
The information in this email is confidential and may be legally privileged.  
It is intended solely for the addressee and access to the email by anyone else 
is unauthorised.
If you are not the intended recipient, any disclosure, copying, distribution or 
any action taken or omitted to be taken in reliance on it, is prohibited and 
may be unlawful.
When addressed to our clients, any opinions or advice contained in this e-mail 
are subject to the terms and conditions expressed  in the governing client 
engagement leter or contract.
If you have received this email in error please notify address@hidden

John Henderson (Holdings) Ltd
Registered office: 9 Hightown Avenue, Mallusk, County Antrim, Northern Ireland, 
BT36 4RT.
Registered in Northern Ireland
Registration Number NI010588
Vat No.: 814 6399 12
*********************************************************************************