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{-# LANGUAGE FlexibleInstances #-}
module Propellor.Property.Spin (Controlled(..), controller) where
import Propellor.Base
import Propellor.Spin (spin)
import Propellor.Types.CmdLine (ControllerChain(..))
import Propellor.Types.Info
class Controlled t where
toHosts :: t -> [Host]
instance Controlled Host where
toHosts h = [h]
instance Controlled [Host] where
toHosts = id
-- | The Host that has this Property is in control of some other Hosts.
--
-- Making a host a controller eliminates the need to manually run
-- propellor --spin to update the controlled hosts. Each time
-- propellor is run on the controller host, it will in turn run
-- propellor on the controlled Hosts.
--
-- Multiple controllers can control the same hosts. However, if
-- propellor is already running on a host, its controller will fail
-- to run it a second time. So, if two controllers both try to
-- control the same host at the same time, one will fail.
--
-- Chains of controllers are supported; host A can control host B which
-- controls host C. Loops of controllers are automatically prevented.
controller :: Controlled h => h -> Property NoInfo
controller h = propertyList "controller" (map controller' (toHosts h))
controller' :: Host -> Property NoInfo
controller' h = property ("controller for " ++ hostName h) $ do
ControllerChain cc <- getControllerChain
if hostName h `elem` cc
then noChange -- avoid loop
else do
liftIO $ spin (hostName h) Nothing (ControllerChain cc) h
-- Don't know if the spin made a change to the
-- remote host or not, but in any case, the
-- local host was not changed.
noChange
getControllerChain :: Propellor ControllerChain
getControllerChain = do
hn <- hostName <$> ask
ControllerChain cc <- fromMaybe (ControllerChain []) . fromInfoVal <$> askInfo
return (ControllerChain (hn:cc))
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