__init__.py

from fabric.api import env

env.use_ssh_config = True
env.forward_agent = True

env.roledefs = {
    # key   # hostname from config
    'foo': ['foo.production'],
}

config

ForwardAgent yes

Host foo.production
    User username
    HostName foo.com
    IdentityFile /path/to/.ssh/keyname_rsa

test.py

from fabric.api import local, run, task, roles

@task
def local_uname():
    local('uname -a')

@roles('foo')
@task
def remote_uname():
    run('uname -a')