--spin can be passed multiple hosts, and it will provision each host in turn.

Note that if it fails to spin a host, it will stop. I think this is better
than continuing to the next, because there might be a reason to spin hosts
in some specific order (ie, update dns first and then use it).

debian/changelog

@@ -6,6 +6,8 @@ propellor (1.0.1) UNRELEASED; urgency=medium
   * --spin target --via relay causes propellor to bounce through an
     intermediate relay host, which handles any necessary uploads
     when provisioning the target host.
+  * --spin can be passed multiple hosts, and it will provision each host
+    in turn.
   * Hostname parameters not containing dots are looked up in the DNS to
     find the full hostname.
   * Added group-related properties. Thanks, Félix Sipma.

doc/usage.mdwn

@@ -20,12 +20,18 @@ action as needed to satisfy the configured properties of the local host.
 
 # OPTIONS
 
-* --spin targethost [--via relayhost]
+* --spin targethost [targethost ...] [--via relayhost]
 
   Causes propellor to automatically install itself on the specified target
   host, or if it's already installed there, push any updates. Propellor is
   then run on the target host, to satisfy its configured properties.
 
+  A signed git commit is made by --spin, so that any changes you have made
+  get propigated to the target host.
+
+  Multiple target hosts can be specified; propellor will run on each of
+  them in sequence.
+
   When run with --via, propellor sshes to the relay host and runs
   `propellor --spin hostname` from there. This can be useful when
   propellor is installing itself, since most of the data transfer

src/Propellor/CmdLine.hs

@@ -39,8 +39,11 @@ usageError ps = do
 processCmdLine :: IO CmdLine
 processCmdLine = go =<< getArgs
   where
-	go ("--spin":h:[]) = Spin <$> hostname h <*> pure Nothing
+	go ("--spin":ps) = case reverse ps of
-	go ("--spin":h:"--via":r:[]) = Spin <$> hostname h <*> pure (Just r)
+		(r:"--via":hs) -> Spin 
+			<$> mapM hostname (reverse hs) 
+			<*> pure (Just r)
+		_ -> Spin <$> mapM hostname ps <*> pure Nothing
 	go ("--add-key":k:[]) = return $ AddKey k
 	go ("--set":f:c:[]) = withprivfield f c Set
 	go ("--dump":f:c:[]) = withprivfield f c Dump
@@ -97,12 +100,14 @@ defaultMain hostlist = do
 	go _ (Update (Just h)) = forceConsole >> fetchFirst (update (Just h))
 	go True cmdline@(Spin _ _) = buildFirst cmdline $ go False cmdline
 	go True cmdline = updateFirst cmdline $ go False cmdline
-	go False (Spin hn r) = withhost hn $ spin hn r
+	go False (Spin hs r) = do
+		commitSpin
+		forM_ hs $ \hn -> withhost hn $ spin hn r
 	go False cmdline@(SimpleRun hn) = buildFirst cmdline $
 		go False (Run hn)
 	go False (Run hn) = ifM ((==) 0 <$> getRealUserID)
 		( onlyprocess $ withhost hn mainProperties
-		, go True (Spin hn Nothing)
+		, go True (Spin [hn] Nothing)
 		)
 
 	withhost :: HostName -> (Host -> IO ()) -> IO ()

src/Propellor/Spin.hs

@@ -1,4 +1,5 @@
 module Propellor.Spin (
+	commitSpin,
 	spin,
 	update,
 	gitPushHelper
@@ -23,9 +24,8 @@ import qualified Propellor.Shim as Shim
 import Utility.FileMode
 import Utility.SafeCommand
 
-spin :: HostName -> Maybe HostName -> Host -> IO ()
+commitSpin :: IO ()
-spin target relay hst = do
+commitSpin = do
-	unless relaying $ do
 	void $ actionMessage "Git commit" $
 		gitCommit [Param "--allow-empty", Param "-a", Param "-m", Param "propellor spin"]
 	-- Push to central origin repo first, if possible.
@@ -35,6 +35,8 @@ spin target relay hst = do
 		void $ actionMessage "Push to central git repository" $
 			boolSystem "git" [Param "push"]
 
+spin :: HostName -> Maybe HostName -> Host -> IO ()
+spin target relay hst = do
 	cacheparams <- if viarelay
 		then pure ["-A"]
 		else toCommand <$> sshCachingParams hn
@@ -78,7 +80,7 @@ spin target relay hst = do
 
 	runcmd = "cd " ++ localdir ++ " && ./propellor " ++ cmd
 	cmd = if viarelay
-		then "--serialized " ++ shellEscape (show (Spin target (Just target)))
+		then "--serialized " ++ shellEscape (show (Spin [target] (Just target)))
 		else "--continue " ++ shellEscape (show (SimpleRun target))
 
 -- Update the privdata, repo url, and git repo over the ssh

src/Propellor/Types.hs

@@ -142,7 +142,7 @@ instance ActionResult Result where
 
 data CmdLine
 	= Run HostName
-	| Spin HostName (Maybe HostName)
+	| Spin [HostName] (Maybe HostName)
 	| SimpleRun HostName
 	| Set PrivDataField Context
 	| Dump PrivDataField Context