Topology configuration update via unix signals!

Updated Network Topology configuration to use optional top level fields

Added tracing to signal handler local config changes

Added explanation on how to update local configuration on the fly to the docs

cardano-node/src/Cardano/Node/Configuration/TopologyP2P.hs

@@ -144,9 +144,9 @@ data NetworkTopology = RealNodeTopology !LocalRootPeersGroups ![PublicRootPeers]
 
 instance FromJSON NetworkTopology where
   parseJSON = withObject "NetworkTopology" $ \o ->
-                RealNodeTopology <$> o .: "LocalRoots"
-                                 <*> o .: "PublicRoots"
-                                 <*> (o .:? "useLedgerAfterSlot" .!= (UseLedger DontUseLedger))
+                RealNodeTopology <$> (o .:? "LocalRoots"     .!= LocalRootPeersGroups [])
+                                 <*> (o .:? "PublicRoots"    .!= [])
+                                 <*> (o .:? "useLedgerAfterSlot" .!= UseLedger DontUseLedger)
 
 instance ToJSON NetworkTopology where
   toJSON top =

cardano-node/src/Cardano/Node/Run.hs

@@ -36,12 +36,13 @@ import           System.Environment (lookupEnv)
 #ifdef UNIX
 import           System.Posix.Files
 import           System.Posix.Types (FileMode)
+import qualified System.Posix.Signals as Signals
 #else
 import           System.Win32.File
 #endif
 
 import           Cardano.BM.Data.LogItem (LOContent (..), LogObject (..), PrivacyAnnotation (..),
-                     mkLOMeta)
+                     mkLOMeta, LOMeta)
 import           Cardano.BM.Data.Tracer (ToLogObject (..), TracingVerbosity (..))
 import           Cardano.BM.Data.Transformers (setHostname)
 import           Cardano.BM.Trace
@@ -230,6 +231,16 @@ handleSimpleNode p trace nodeTracers nc onKernel = do
   publicRootsVar <- newTVarIO publicRoots
   useLedgerVar <- newTVarIO (useLedgerAfterSlot nt)
 
+#ifdef UNIX
+  _ <- Signals.installHandler
+        Signals.sigHUP
+        (updateVars meta localRootsVar publicRootsVar useLedgerVar)
+        Nothing
+#endif
+  traceNamedObject
+          (appendName "signal-handler" trace)
+          (meta, LogMessage (Text.pack "Installed signal handler"))
+
   let
       diffusionArguments :: DiffusionArguments IO
       diffusionArguments =
@@ -257,6 +268,9 @@ handleSimpleNode p trace nodeTracers nc onKernel = do
   traceNamedObject
     (appendName "public-roots" trace)
     (meta, LogMessage . Text.pack . show $ publicRoots)
+  traceNamedObject
+    (appendName "use-ledger-after-slot" trace)
+    (meta, LogMessage . Text.pack . show $ useLedgerAfterSlot nt)
   traceNamedObject
     (appendName "local-socket" trace)
     (meta, LogMessage . Text.pack . show $ localSocketOrPath)
@@ -315,6 +329,39 @@ handleSimpleNode p trace nodeTracers nc onKernel = do
     forM_ basicInfoItems $ \(LogObject nm mt content) ->
       traceNamedObject (appendName nm tr) (mt, content)
 
+#ifdef UNIX
+  updateVars :: LOMeta
+             -> StrictTVar IO [(Int, Map RelayAddress PeerAdvertise)]
+             -> StrictTVar IO [RelayAddress]
+             -> StrictTVar IO UseLedgerAfter
+             -> Signals.Handler
+  updateVars meta localRootsVar publicRootsVar useLedgerVar =
+    Signals.Catch $ do
+      traceNamedObject
+          (appendName "signal-handler" trace)
+          (meta, LogMessage (Text.pack "SIGHUP signal received - Performing topology configuration update"))
+
+      eitherTopology <- readTopologyFile nc
+      nt <- either (\err -> panic $ "Cardano.Node.Run.handleSimpleNode.readTopologyFile: " <> err) pure eitherTopology
+
+      let (localRoots, publicRoots) = producerAddresses nt
+
+      atomically $ do
+        writeTVar localRootsVar localRoots
+        writeTVar publicRootsVar publicRoots
+        writeTVar useLedgerVar (useLedgerAfterSlot nt)
+
+      traceNamedObject
+        (appendName "local-roots" trace)
+        (meta, LogMessage . Text.pack . show $ localRoots)
+      traceNamedObject
+        (appendName "public-roots" trace)
+        (meta, LogMessage . Text.pack . show $ publicRoots)
+      traceNamedObject
+        (appendName "use-ledger-after-slot" trace)
+        (meta, LogMessage . Text.pack . show $ useLedgerAfterSlot nt)
+#endif
+
 --------------------------------------------------------------------------------
 -- Helper functions
 --------------------------------------------------------------------------------

doc/getting-started/understanding-config-files.md

@@ -50,12 +50,15 @@ Tells your node to which nodes in the network it should talk to. A minimal versi
     dns domain `y.y.y.y` (assuming they are), and try to maintain a connection with at least `1` of the
     resolved ips.
 
-* `isDomain` tells if a given address is a dns address or not. If true and object `domain: { domain, port }` should be specified instead.
-
 * `valency` tells the node how many connections your node should try to pick from the given group. If a dns address is given, valency governs to how many resolved ip addresses should we maintain active (hot) connection.
 
 Your __block-producing__ node must __ONLY__ talk to your __relay nodes__, and the relay node should talk to other relay nodes in the network.
 
+You __can__ tell the node that the topology configuration file changed by sending a SIGHUP
+signal to the `cardano-node` process, e.g. `pkill -HUP cardano-node`. After receiving the
+signal, `cardano-node` will re-read the file and restart all dns resolution. Please
+**note** that this only applies to the topology configuration file!
+
 #### The genesis.json file
 
 The genesis file is generated with the `cardano-cli` by reading a `genesis.spec.json` file, which is out of scope for this document.