Implement role switching.

arangod/Cluster/ServerState.cpp

@@ -665,6 +665,36 @@ void ServerState::setDisableDispatcherKickstarter (bool value) {
   _disableDispatcherKickstarter = value;
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// @brief redetermine the server role, we do this after a plan change.
+/// This is needed for automatic failover. This calls determineRole with 
+/// previous values of _info and _id. In particular, the _id will usually
+/// already be set. If the current role cannot be determined from the
+/// agency or is not unique, then the system keeps the old role.
+/// Returns true if there is a change and false otherwise.
+////////////////////////////////////////////////////////////////////////////////
+
+bool ServerState::redetermineRole () {
+  std::string saveIdOfPrimary = _idOfPrimary;
+  RoleEnum role = determineRole(_localInfo, _id);
+  std::string roleString = roleToString(role);
+  LOG_INFO("Redetermined role from agency: %s", roleString.c_str());
+  if (role == ServerState::ROLE_UNDEFINED) {
+    return false;
+  }
+  RoleEnum oldRole = loadRole();
+  if (role != oldRole) {
+    LOG_INFO("Changed role to: %s", roleString.c_str());
+    storeRole(role);
+    return true;
+  }
+  if (_idOfPrimary != saveIdOfPrimary) {
+    LOG_INFO("The ID of our primary has changed!");
+    return true;
+  }
+  return false;
+}
+
 // -----------------------------------------------------------------------------
 // --SECTION--                                                   private methods
 // -----------------------------------------------------------------------------

arangod/Cluster/ServerState.h

@@ -399,6 +399,17 @@ namespace triagens {
 
         void setDisableDispatcherKickstarter (bool);
 
+////////////////////////////////////////////////////////////////////////////////
+/// @brief redetermine the server role, we do this after a plan change.
+/// This is needed for automatic failover. This calls determineRole with 
+/// previous values of _info and _id. In particular, the _id will usually
+/// already be set. If the current role cannot be determined from the
+/// agency or is not unique, then the system keeps the old role.
+/// Returns true if there is a change and false otherwise.
+////////////////////////////////////////////////////////////////////////////////
+
+        bool redetermineRole ();
+
 // -----------------------------------------------------------------------------
 // --SECTION--                                                   private methods
 // -----------------------------------------------------------------------------

arangod/Cluster/v8-cluster.cpp

@@ -1511,6 +1511,28 @@ static void JS_SetRoleServerState (const v8::FunctionCallbackInfo<v8::Value>& ar
   TRI_V8_TRY_CATCH_END
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// @brief redetermines the role from the agency
+////////////////////////////////////////////////////////////////////////////////
+
+static void JS_RedetermineRoleServerState (const v8::FunctionCallbackInfo<v8::Value>& args) {
+  TRI_V8_TRY_CATCH_BEGIN(isolate);
+  v8::HandleScope scope(isolate);
+
+  if (args.Length() != 0) {
+    TRI_V8_THROW_EXCEPTION_USAGE("redetermineRole()");
+  }
+
+  bool changed = ServerState::instance()->redetermineRole();
+  if (changed) {
+    TRI_V8_RETURN_TRUE();
+  }
+  else {
+    TRI_V8_RETURN_FALSE();
+  }
+  TRI_V8_TRY_CATCH_END
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// @brief returns the server state
 ////////////////////////////////////////////////////////////////////////////////
@@ -2201,6 +2223,7 @@ void TRI_InitV8Cluster (v8::Isolate* isolate, v8::Handle<v8::Context> context) {
   TRI_AddMethodVocbase(isolate, rt, TRI_V8_ASCII_STRING("setLocalInfo"), JS_SetLocalInfoServerState, true);
   TRI_AddMethodVocbase(isolate, rt, TRI_V8_ASCII_STRING("setId"), JS_SetIdServerState, true);
   TRI_AddMethodVocbase(isolate, rt, TRI_V8_ASCII_STRING("setRole"), JS_SetRoleServerState, true);
+  TRI_AddMethodVocbase(isolate, rt, TRI_V8_ASCII_STRING("redetermineRole"), JS_RedetermineRoleServerState, true);
   TRI_AddMethodVocbase(isolate, rt, TRI_V8_ASCII_STRING("status"), JS_StatusServerState);
   TRI_AddMethodVocbase(isolate, rt, TRI_V8_ASCII_STRING("getClusterAuthentication"), JS_GetClusterAuthentication);
 

js/server/modules/org/arangodb/cluster.js

@@ -829,13 +829,97 @@ function setupReplication () {
   db._useDatabase("_system");
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// @brief role change from secondary to primary
+////////////////////////////////////////////////////////////////////////////////
+
+function secondaryToPrimary () {
+  console.info("Switching role from secondary to primary...");
+  var db = require("internal").db;
+  var rep = require("org/arangodb/replication");
+  var dbs = db._listDatabases();
+  var i;
+  try {
+    for (i = 0; i < dbs.length; i++) {
+      var database = dbs[i];
+      console.info("Stopping asynchronous replication for db " +
+                   database + "...");
+      db._useDatabase(database);
+      var state = rep.applier.state();
+      if (state.state.running === true) {
+        try {
+          rep.applier.stop();
+        }
+        catch (err) {
+          console.info("Exception caught whilst stopping replication!");
+        }
+      }
+      rep.applier.forget();
+    }
+  }
+  finally {
+    db._useDatabase("_system");
+  }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+/// @brief role change from primary to secondary
+////////////////////////////////////////////////////////////////////////////////
+
+function primaryToSecondary () {
+  console.info("Switching role from primary to secondary...");
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// @brief change handling trampoline function
 ////////////////////////////////////////////////////////////////////////////////
 
 function handleChanges (plan, current) {
-  handleDatabaseChanges(plan, current);
+  var changed = false;
   var role = ArangoServerState.role();
+  if (role === "PRIMARY" || role === "SECONDARY") {
+    // Need to check role change for automatic failover:
+    var myId = ArangoServerState.id();
+    if (role === "PRIMARY") {
+      if (! plan.hasOwnProperty("Plan/DBServers/"+myId)) {
+        // Ooops! We do not seem to be a primary any more!
+        changed = ArangoServerState.redetermineRole();
+      }
+    }
+    else { // role === "SECONDARY"
+      if (plan.hasOwnProperty("Plan/DBServers/"+myId)) {
+        // Ooops! We are now a primary!
+        changed = ArangoServerState.redetermineRole();
+      }
+      else {
+        var found = null;
+        var p;
+        for (p in plan) {
+          if (plan.hasOwnProperty(p) && plan[p] === myId) {
+            found = p;
+            break;
+          }
+        }
+        if (found !== ArangoServerState.idOfPrimary()) {
+          // Note this includes the case that we are not found at all!
+          changed = ArangoServerState.redetermineRole();
+        }
+      }
+    }
+  }
+  var oldRole = role;
+  if (changed) {
+    role = ArangoServerState.role();
+    console.log("Our role has changed to " + role);
+    if (oldRole === "SECONDARY" && role === "PRIMARY") {
+      secondaryToPrimary();
+    }
+    else if (oldRole === "PRIMARY" && role === "SECONDARY") {
+      primaryToSecondary();
+    }
+  }
+
+  handleDatabaseChanges(plan, current);
   if (role === "PRIMARY" || role === "COORDINATOR") {
     // Note: This is only ever called for DBservers (primary and secondary),
     // we keep the coordinator case here just in case...