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is_leader requires juju 1.22.0 or better #16

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merged 5 commits into from Aug 10, 2015
Merged

is_leader requires juju 1.22.0 or better #16

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5d4e1cc
is_leader requires juju 1.22.0 or better
Aug 10, 2015
e374801
Refactor the implementation away from semver check
Aug 10, 2015
23d17ca
Refactored is_leader
Aug 10, 2015
a2efbc1
refactor the error message, and properly scope to a CRITICAL warning
Aug 10, 2015
e9efc9b
Add a blurb to the README about Juju minimum version
Aug 10, 2015
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21 changes: 21 additions & 0 deletions hooks/hooks.py
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Expand Up @@ -24,6 +24,10 @@

@hooks.hook('config-changed')
def config_changed():
if not isleader_available:
hookenv.log('This charm requires Juju 1.22.0 or greater. Panic and exit!'
'CRITICAL')
sys.exit(1)
if not db.get('installed') or hookenv.config().changed('source-sum'):
install_etcd()
if leader_status:
Expand Down Expand Up @@ -152,6 +156,23 @@ def install_etcd():
hookenv.open_port(4001)
db.set('installed', True)

def isleader_available():
"""Attempt to locate is_leader

predicate method to determine if we are on a Juju revision that maintains
the leader election codebase.
"""
cmd = ['which', 'is_leader']
try:
ret = subprocess.call(cmd, universal_newlines=True)
if ret == 0:
return True
else:
return False
except OSError as e:
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I'd remove the entire try block here, since OSError will simply raise just like any other exception. There really isn't any exception handling here. You can also simplify the if block with

return ret == 0

Finally, it appears that charmhelpers has some way of translating whether or not is-leader is available. Doing this

from charmhelpers.core.hookenv import is_leader

try:
    is_leader()
except NotImplementedError:
    print("panic message")

would achieve the same goal.

# If we aren't finding the which command, we have bigger issues.
raise

if __name__ == '__main__':
with hook_data():
hooks.execute(sys.argv)