SERVER-8710 check balancer is stopped before upgrading to nonzero config version

1 files changed, 46 insertions, 2 deletions

diff --git a/src/mongo/s/config_upgrade.cpp b/src/mongo/s/config_upgrade.cpp
index 1ac1d72d1c8..a68ff7bf6d9 100644
--- a/src/mongo/s/config_upgrade.cpp
+++ b/src/mongo/s/config_upgrade.cpp
@@ -25,6 +25,7 @@
 #include "mongo/s/mongo_version_range.h"
 #include "mongo/s/type_config_version.h"
 #include "mongo/s/type_database.h"
+#include "mongo/s/type_settings.h"
 #include "mongo/s/type_shard.h"
 #include "mongo/util/assert_util.h"
 #include "mongo/util/version.h"
@@ -277,6 +278,30 @@ namespace mongo {
         return VersionStatus_NeedUpgrade;
     }
 
+    // Returns true if we can confirm the balancer is stopped
+    bool _isBalancerStopped(const ConnectionString& configLoc, string* errMsg) {
+        
+        // Get the balancer information
+        scoped_ptr<ScopedDbConnection> connPtr;
+        
+        BSONObj balancerDoc;
+        try {
+            connPtr.reset(ScopedDbConnection::getInternalScopedDbConnection(configLoc, 30));
+            ScopedDbConnection& conn = *connPtr;
+            
+            balancerDoc = conn->findOne(SettingsType::ConfigNS,
+                                        BSON(SettingsType::key("balancer")));
+        }
+        catch (const DBException& e) {
+            *errMsg = e.toString();
+            return false;
+        }
+
+        connPtr->done();
+        
+        return balancerDoc[SettingsType::balancerStopped()].trueValue();
+    }
+
     // Checks that all config servers are online
     bool _checkConfigServersAlive(const ConnectionString& configLoc, string* errMsg) {
         
@@ -429,8 +454,11 @@ namespace mongo {
         // if possible.
         //
 
+        // The first empty version is technically an upgrade, but has special semantics
+        bool isEmptyVersion = versionInfo->getCurrentVersion() == UpgradeHistory_EmptyVersion;
+
         // First check for the upgrade flag (but no flag is needed if we're upgrading from empty)
-        if (!versionInfo->getCurrentVersion() == UpgradeHistory_EmptyVersion && !upgrade) {
+        if (!isEmptyVersion && !upgrade) {
 
             *errMsg = stream() << "newer version " << CURRENT_CONFIG_VERSION
                                << " of mongo config metadata is required, " << "current version is "
@@ -443,8 +471,24 @@ namespace mongo {
         // Contact the config servers to make sure all are online - otherwise we wait a long time
         // for locks.
         if (!_checkConfigServersAlive(configLoc, errMsg)) {
+
+            if (isEmptyVersion) {
+                *errMsg = stream() << "all config servers must be reachable for initial"
+                                   << " config database creation" << causedBy(errMsg);
+            }
+            else {
+                *errMsg = stream() << "all config servers must be reachable for config upgrade"
+                                   << causedBy(errMsg);
+            }
+            
+            return false;
+        }
+
+        // Check whether or not the balancer is online, if it is online we will not upgrade
+        // (but we will initialize the config server)
+        if (!isEmptyVersion && !_isBalancerStopped(configLoc, errMsg)) {
             
-            *errMsg = stream() << "all config servers must be reachable for config upgrade"
+            *errMsg = stream() << "balancer must be stopped for config upgrade"
                                << causedBy(errMsg);
             
             return false;