Hello everyone. I'm taking my first steps in Cloud Haskell and got some unexpected behaviors. I used the code from Raspberry Pi in a Haskell Cloud [1] as a first example. Did try to switch the code to use Template Haskell with no luck, stick with the verbose style. I changed some of the code, from ProcessId-based messaging to typed channel to receive the Pong; using "startSlave" to start the worker nodes; and changed the master node to loop forever sending pings to the worker nodes. The unexpected behaviors: - Dropping a worker node while the master is running makes the master node to crash. - Master node do not see worker nodes started after the master process. In order to fix this, I tried to "findSlaves" at the start of the master process and send ping to only these ones, ignoring the list of NodeId enforced by the type signature of "startMaster". Now the master finds new slaves. The bad thing is that when I close one of the workers, the master process freezes. It simply stop doing anything. No more messages and no more Pings to other slaves. :( My view of Cloud Haskell usage would be something similar to this: a master node sending work to slaves; slave instances getting up or down based on demand. So, the master node should be slave-failure-proof and also find new slaves somehow. Am I misunderstanding the big picture of Cloud Haskell or doing anything wrong in the following code? Code (skipped imports and wiring stuff): -- newtype Ping = Ping (SendPort Pong) deriving (Typeable, Binary, Show) newtype Pong = Pong ProcessId deriving (Typeable, Binary, Show) worker :: Ping -> Process () worker (Ping sPong) = do wId <- getSelfPid say "Got a Ping!" sendChan sPong (Pong wId) master :: Backend -> [NodeId] -> Process () master backend _ = forever $ do workers <- findSlaves backend say $ "Slaves: " ++ show workers (sPong, rPong) <- newChan forM_ workers $ \w -> do say $ "Sending a Ping to " ++ (show w) ++ "..." spawn w (workerClosure (Ping sPong)) say $ "Waiting for reply from " ++ (show (length workers)) ++ " worker(s)" replicateM_ (length workers) $ do (Pong wId) <- receiveChan rPong say $ "Got back a Pong from " ++ (show $ processNodeId wId) ++ "!" (liftIO . threadDelay) 2000000 -- Wait a bit before return main = do prog <- getProgName args <- getArgs case args of ["master", host, port] -> do backend <- initializeBackend host port remoteTable startMaster backend (master backend) ["worker", host, port] -> do backend <- initializeBackend host port remoteTable startSlave backend _ -> putStrLn $ "usage: " ++ prog ++ " (master | worker) host port" -- [1] http://alenribic.com/writings/post/raspberry-pi-in-a-haskell-cloud