SERVER-43904: Filter unelectable nodes during election handoff

7 files changed, 70 insertions, 3 deletions

diff --git a/etc/backports_required_for_multiversion_tests.yml b/etc/backports_required_for_multiversion_tests.yml
index 3c56b35a468..f3caa752b68 100644
--- a/etc/backports_required_for_multiversion_tests.yml
+++ b/etc/backports_required_for_multiversion_tests.yml
@@ -86,6 +86,8 @@ all:
     test_file: jstests/replsets/read_operations_during_rollback.js
   - ticket: SERVER-51262
     test_file: jstests/replsets/transactions_on_secondaries_not_allowed.js
+  - ticket: SERVER-43904
+    test_file: jstests/replsets/election_handoff_skips_unelectable_nodes.js
 
 # Tests that should only be excluded from particular suites should be listed under that suite.
 suites:
diff --git a/jstests/replsets/election_handoff_skips_unelectable_nodes.js b/jstests/replsets/election_handoff_skips_unelectable_nodes.js
new file mode 100644
index 00000000000..d2bc8672e4a
--- /dev/null
+++ b/jstests/replsets/election_handoff_skips_unelectable_nodes.js
@@ -0,0 +1,25 @@
+/*
+ * Tests that election handoff will not attempt to step up a node that is unelectable.
+ */
+
+(function() {
+"use strict";
+
+load("jstests/replsets/libs/election_handoff.js");
+
+const rst = new ReplSetTest({name: jsTestName(), nodes: 3});
+rst.startSet();
+
+// Make sure there are no election timeouts firing for the duration of the test. This helps
+// ensure that the test will only pass if the election handoff succeeds.
+rst.initiateWithHighElectionTimeout();
+
+// Freeze one of the secondaries so that it cannot be elected. As a result, the other secondary
+// should always be chosen to run for primary via election handoff.
+const frozenSecondary = rst.getSecondaries()[0];
+assert.commandWorked(frozenSecondary.adminCommand({replSetFreeze: ReplSetTest.kForeverSecs}));
+
+ElectionHandoffTest.testElectionHandoff(rst, 0, 2);
+
+rst.stopSet();
+})();
diff --git a/jstests/sharding/move_chunk_with_session_helper.js b/jstests/sharding/move_chunk_with_session_helper.js
index bf4653eb18a..63d94a81c01 100644
--- a/jstests/sharding/move_chunk_with_session_helper.js
+++ b/jstests/sharding/move_chunk_with_session_helper.js
@@ -6,7 +6,7 @@ load("jstests/replsets/rslib.js");
  * 2. Perform writes.
  * 3. Migrate only chunk to other shard.
  * 4. Retry writes.
- * 5. Step down primary and wait for new primary.
+ * 5. Step up secondary and wait for new primary.
  * 6. Retry writes.
  * 7. Migrate only chunk back to original shard.
  * 8. Retry writes.
@@ -27,8 +27,8 @@ var testMoveChunkWithSession = function(
     checkRetryResultFunc(result, assert.commandWorked(testDB.runCommand(cmdObj)));
     checkDocumentsFunc(coll);
 
-    assert.commandWorked(
-        st.rs1.getPrimary().adminCommand({replSetStepDown: 60, secondaryCatchUpPeriodSecs: 30}));
+    const secondary = st.rs1.getSecondary();
+    st.rs1.stepUp(secondary);
 
     st.rs1.awaitNodesAgreeOnPrimary();
     st.configRS.nodes.concat([st.s]).forEach(function awaitNode(conn) {
diff --git a/src/mongo/db/repl/member_data.h b/src/mongo/db/repl/member_data.h
index b6344838d9b..1903a1b448d 100644
--- a/src/mongo/db/repl/member_data.h
+++ b/src/mongo/db/repl/member_data.h
@@ -151,6 +151,13 @@ public:
         return _hostAndPort;
     }
 
+    /*
+     * Returns true if the last heartbeat data explicilty stated that the node is not electable.
+     */
+    bool isUnelectable() const {
+        return _lastResponse.hasIsElectable() && !_lastResponse.isElectable();
+    }
+
     /**
      * Sets values in this object from the results of a successful heartbeat command.
      * Returns true if the lastApplied/lastDurable values advanced or we've received a newer
diff --git a/src/mongo/db/repl/repl_set_heartbeat_response.cpp b/src/mongo/db/repl/repl_set_heartbeat_response.cpp
index 138f6c84e1e..c77d454f00c 100644
--- a/src/mongo/db/repl/repl_set_heartbeat_response.cpp
+++ b/src/mongo/db/repl/repl_set_heartbeat_response.cpp
@@ -63,6 +63,7 @@ const std::string kReplSetFieldName = "set";
 const std::string kSyncSourceFieldName = "syncingTo";
 const std::string kTermFieldName = "term";
 const std::string kTimestampFieldName = "ts";
+const std::string kIsElectableFieldName = "electable";
 
 }  // namespace
 
@@ -102,6 +103,9 @@ void ReplSetHeartbeatResponse::addToBSON(BSONObjBuilder* builder) const {
         _appliedOpTime.append(builder, kAppliedOpTimeFieldName);
         builder->appendDate(kAppliedWallTimeFieldName, _appliedWallTime);
     }
+    if (_electableSet) {
+        *builder << kIsElectableFieldName << _electable;
+    }
 }
 
 BSONObj ReplSetHeartbeatResponse::toBSON() const {
@@ -180,6 +184,13 @@ Status ReplSetHeartbeatResponse::initialize(const BSONObj& doc, long long term)
     _appliedWallTime = appliedWallTimeElement.Date();
     _appliedOpTimeSet = true;
 
+    status = bsonExtractBooleanField(doc, kIsElectableFieldName, &_electable);
+    if (!status.isOK()) {
+        _electableSet = false;
+    } else {
+        _electableSet = true;
+    }
+
     const BSONElement memberStateElement = doc[kMemberStateFieldName];
     if (memberStateElement.eoo()) {
         _stateSet = false;
@@ -300,5 +311,10 @@ OpTimeAndWallTime ReplSetHeartbeatResponse::getDurableOpTimeAndWallTime() const
     return {_durableOpTime, _durableWallTime};
 }
 
+bool ReplSetHeartbeatResponse::isElectable() const {
+    invariant(_electableSet);
+    return _electable;
+}
+
 }  // namespace repl
 }  // namespace mongo
diff --git a/src/mongo/db/repl/repl_set_heartbeat_response.h b/src/mongo/db/repl/repl_set_heartbeat_response.h
index 44fe581f23f..300e9afb84b 100644
--- a/src/mongo/db/repl/repl_set_heartbeat_response.h
+++ b/src/mongo/db/repl/repl_set_heartbeat_response.h
@@ -115,6 +115,10 @@ public:
     }
     OpTime getDurableOpTime() const;
     OpTimeAndWallTime getDurableOpTimeAndWallTime() const;
+    bool hasIsElectable() const {
+        return _electableSet;
+    }
+    bool isElectable() const;
 
     /**
      * Sets _setName to "name".
@@ -185,6 +189,10 @@ public:
     void setTerm(long long term) {
         _term = term;
     }
+    void setElectable(bool electable) {
+        _electableSet = true;
+        _electable = electable;
+    }
 
 private:
     bool _electionTimeSet = false;
@@ -212,6 +220,9 @@ private:
     bool _primaryIdSet = false;
     long long _primaryId = -1;
     long long _term = -1;
+
+    bool _electableSet = false;
+    bool _electable = false;
 };
 
 }  // namespace repl
diff --git a/src/mongo/db/repl/topology_coordinator.cpp b/src/mongo/db/repl/topology_coordinator.cpp
index 8cefab5e3bc..b81faaab756 100644
--- a/src/mongo/db/repl/topology_coordinator.cpp
+++ b/src/mongo/db/repl/topology_coordinator.cpp
@@ -846,6 +846,9 @@ Status TopologyCoordinator::prepareHeartbeatResponseV1(Date_t now,
         return Status::OK();
     }
 
+    response->setElectable(
+        !_getMyUnelectableReason(now, StartElectionReasonEnum::kElectionTimeout));
+
     const long long v = _rsConfig.getConfigVersion();
     const long long t = _rsConfig.getConfigTerm();
     response->setConfigVersion(v);
@@ -2331,6 +2334,9 @@ TopologyCoordinator::UnelectableReasonMask TopologyCoordinator::_getUnelectableR
     if (hbData.getState() != MemberState::RS_SECONDARY) {
         result |= NotSecondary;
     }
+    if (hbData.up() && hbData.isUnelectable()) {
+        result |= StepDownPeriodActive;
+    }
     invariant(result || memberConfig.isElectable());
     return result;
 }