[Fab-user] Providing a fallback for roles at runtime

[Paul Walsh]

I have a setup like this:

env.roledefs = {'default': ['1.2.3.4'], 'db': ['5.6.7.8']},
env.roles: ['default', 'db']
# other custom keys on env

@roles('db')
@task
def drop():
utilities.alert(u'Dropping the database.')
run('dropdb {name}'.format(name=env.db_name))


This is fine: the task only executes for the 'db' role, as expected.

But, this is part of a larger set of tasks that I have. And, what I actually want to do is say:

"execute this task on db if db is in roles, otherwise, execute on default."

So, to achieve that, I tried:

import utilities

@roles(utilities.get_role('db'))
@task
def drop():
utilities.alert(u'Dropping the database.')
run('dropdb {name}'.format(name=env.db_name))


# utilities.py
def get_role(target_role):
if target_role in env.roles:
return target_role
else:
return 'default'


However, the task still attempts to run on roles['default']. I'm diving in but I'm also wondering if there is another way I could, in the fabfile itself, dynamically set the role for a task like this.

[Michael Gliwinski]

On Thursday 19 Dec 2013 08:44:15 Paul Walsh wrote:
...

Post by Paul Walsh
"execute this task on db if db is in roles, otherwise, execute on default."
import utilities
@roles(utilities.get_role('db'))
@task
utilities.alert(u'Dropping the database.')
run('dropdb {name}'.format(name=env.db_name))
# utilities.py
return target_role
return 'default'
However, the task still attempts to run on roles['default']. I'm diving in
but I'm also wondering if there is another way I could, in the fabfile
itself, dynamically set the role for a task like this.

I'm not sure how you set env.roles, but note that utilities.get_role will be
executed when your fabfile is loaded.

Roles can actually be callables, so you could do something like:

def db_or_default():
if ...: return ['5.6.7.8']
return env.roledefs['default']

env.roledefs = {'default': ['1.2.3.4'], 'db': db_or_default}


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