SERVER-45080 ignore voteRequest from nodes with lower configs

5 files changed, 173 insertions, 49 deletions

diff --git a/src/mongo/db/repl/repl_set_request_votes_args.cpp b/src/mongo/db/repl/repl_set_request_votes_args.cpp
index 57256d71554..3c8538606ed 100644
--- a/src/mongo/db/repl/repl_set_request_votes_args.cpp
+++ b/src/mongo/db/repl/repl_set_request_votes_args.cpp
@@ -33,6 +33,7 @@
 #include "mongo/bson/util/bson_extract.h"
 #include "mongo/db/jsobj.h"
 #include "mongo/db/repl/bson_extract_optime.h"
+#include "mongo/db/server_options.h"
 
 namespace mongo {
 namespace repl {
@@ -41,6 +42,7 @@ namespace {
 const std::string kCandidateIndexFieldName = "candidateIndex";
 const std::string kCommandName = "replSetRequestVotes";
 const std::string kConfigVersionFieldName = "configVersion";
+const std::string kConfigTermFieldName = "configTerm";
 const std::string kDryRunFieldName = "dryRun";
 // The underlying field name is inaccurate, but changing it requires a fair amount of cross
 // compatibility work for no real benefit.
@@ -56,6 +58,7 @@ const std::string kLegalArgsFieldNames[] = {
     kCandidateIndexFieldName,
     kCommandName,
     kConfigVersionFieldName,
+    kConfigTermFieldName,
     kDryRunFieldName,
     kLastDurableOpTimeFieldName,
     kSetNameFieldName,
@@ -84,6 +87,13 @@ Status ReplSetRequestVotesArgs::initialize(const BSONObj& argsObj) {
     if (!status.isOK())
         return status;
 
+    // In order to be compatible with FCV 4.2, default the config term to -1 if we are unable
+    // parse a configTerm field from the args.
+    status = bsonExtractIntegerFieldWithDefault(
+        argsObj, kConfigTermFieldName, OpTime::kUninitializedTerm, &_cfgterm);
+    if (!status.isOK())
+        return status;
+
     status = bsonExtractStringField(argsObj, kSetNameFieldName, &_setName);
     if (!status.isOK())
         return status;
@@ -115,6 +125,10 @@ long long ReplSetRequestVotesArgs::getConfigVersion() const {
     return _cfgver;
 }
 
+long long ReplSetRequestVotesArgs::getConfigTerm() const {
+    return _cfgterm;
+}
+
 OpTime ReplSetRequestVotesArgs::getLastDurableOpTime() const {
     return _lastDurableOpTime;
 }
@@ -130,6 +144,12 @@ void ReplSetRequestVotesArgs::addToBSON(BSONObjBuilder* builder) const {
     builder->append(kTermFieldName, _term);
     builder->appendIntOrLL(kCandidateIndexFieldName, _candidateIndex);
     builder->appendIntOrLL(kConfigVersionFieldName, _cfgver);
+    // Only append the config term field if we are in FCV 4.4
+    if (serverGlobalParams.featureCompatibility.isVersionInitialized() &&
+        serverGlobalParams.featureCompatibility.getVersion() ==
+            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44) {
+        builder->appendIntOrLL(kConfigTermFieldName, _cfgterm);
+    }
     _lastDurableOpTime.append(builder, kLastDurableOpTimeFieldName);
 }
 
diff --git a/src/mongo/db/repl/repl_set_request_votes_args.h b/src/mongo/db/repl/repl_set_request_votes_args.h
index dfecbdba4d4..1dc74eb4f12 100644
--- a/src/mongo/db/repl/repl_set_request_votes_args.h
+++ b/src/mongo/db/repl/repl_set_request_votes_args.h
@@ -47,6 +47,7 @@ public:
     long long getTerm() const;
     long long getCandidateIndex() const;
     long long getConfigVersion() const;
+    long long getConfigTerm() const;
     OpTime getLastDurableOpTime() const;
     bool isADryRun() const;
 
@@ -58,7 +59,9 @@ private:
     long long _term = -1;  // Current known term of the command issuer.
     // replSet config index of the member who sent the replSetRequestVotesCmd.
     long long _candidateIndex = -1;
-    long long _cfgver = -1;     // replSet config version known to the command issuer.
+    long long _cfgver = -1;  // replSet config version known to the command issuer.
+    // replSet config term known to the command issuer.
+    long long _cfgterm = OpTime::kUninitializedTerm;
     OpTime _lastDurableOpTime;  // The last known durable op of the command issuer.
     bool _dryRun = false;       // Indicates this is a pre-election check when true.
 };
diff --git a/src/mongo/db/repl/topology_coordinator.cpp b/src/mongo/db/repl/topology_coordinator.cpp
index df4e7132293..8f7dca8cdcd 100644
--- a/src/mongo/db/repl/topology_coordinator.cpp
+++ b/src/mongo/db/repl/topology_coordinator.cpp
@@ -2748,41 +2748,60 @@ void TopologyCoordinator::processReplSetRequestVotes(const ReplSetRequestVotesAr
         return;
     }
 
+    // If either config term is -1, ignore the config term entirely and compare config versions.
+    bool compareConfigTerms = args.getConfigTerm() != -1 && _rsConfig.getConfigTerm() != -1;
+
     if (args.getTerm() < _term) {
         response->setVoteGranted(false);
-        response->setReason(str::stream() << "candidate's term (" << args.getTerm()
-                                          << ") is lower than mine (" << _term << ")");
-    } else if (args.getConfigVersion() != _rsConfig.getConfigVersion()) {
+        response->setReason(str::stream() << "candidate's term ({}) is lower than mine ({})"_format(
+                                args.getTerm(), _term));
+    } else if (compareConfigTerms && args.getConfigTerm() < _rsConfig.getConfigTerm()) {
+        response->setVoteGranted(false);
+        response->setReason(str::stream()
+                            << "candidate's term in config(term, version): ({}, {}) is lower "
+                               "than mine ({}, {})"_format(args.getConfigTerm(),
+                                                           args.getConfigVersion(),
+                                                           _rsConfig.getConfigTerm(),
+                                                           _rsConfig.getConfigVersion()));
+    } else if ((!compareConfigTerms || args.getConfigTerm() == _rsConfig.getConfigTerm()) &&
+               args.getConfigVersion() < _rsConfig.getConfigVersion()) {
+        // If the terms should not be compared or if the terms are equal, fall back to version
+        // comparison.
         response->setVoteGranted(false);
         response->setReason(str::stream()
-                            << "candidate's config version (" << args.getConfigVersion()
-                            << ") differs from mine (" << _rsConfig.getConfigVersion() << ")");
+                            << "ignoring term of -1 for comparison, candidate's version in "
+                               "config(term, version): ({}, {}) is lower than mine ({}, {})"_format(
+                                   args.getConfigTerm(),
+                                   args.getConfigVersion(),
+                                   _rsConfig.getConfigTerm(),
+                                   _rsConfig.getConfigVersion()));
     } else if (args.getSetName() != _rsConfig.getReplSetName()) {
         response->setVoteGranted(false);
         response->setReason(str::stream()
-                            << "candidate's set name (" << args.getSetName()
-                            << ") differs from mine (" << _rsConfig.getReplSetName() << ")");
+                            << "candidate's set name ({}) differs from mine ({})"_format(
+                                   args.getSetName(), _rsConfig.getReplSetName()));
     } else if (args.getLastDurableOpTime() < getMyLastAppliedOpTime()) {
         response->setVoteGranted(false);
-        response
-            ->setReason(str::stream()
-                        << "candidate's data is staler than mine. candidate's last applied OpTime: "
-                        << args.getLastDurableOpTime().toString()
-                        << ", my last applied OpTime: " << getMyLastAppliedOpTime().toString());
+        response->setReason(str::stream()
+                            << "candidate's data is staler than mine. candidate's last applied "
+                               "OpTime: {}, my last applied OpTime: {}"_format(
+                                   args.getLastDurableOpTime().toString(),
+                                   getMyLastAppliedOpTime().toString()));
     } else if (!args.isADryRun() && _lastVote.getTerm() == args.getTerm()) {
         response->setVoteGranted(false);
-        response->setReason(str::stream()
-                            << "already voted for another candidate ("
-                            << _rsConfig.getMemberAt(_lastVote.getCandidateIndex()).getHostAndPort()
-                            << ") this term (" << _lastVote.getTerm() << ")");
+        response->setReason(
+            str::stream() << "already voted for another candidate ({}) this "
+                             "term ({})"_format(_rsConfig.getMemberAt(_lastVote.getCandidateIndex())
+                                                    .getHostAndPort(),
+                                                _lastVote.getTerm()));
     } else {
         int betterPrimary = _findHealthyPrimaryOfEqualOrGreaterPriority(args.getCandidateIndex());
         if (_selfConfig().isArbiter() && betterPrimary >= 0) {
             response->setVoteGranted(false);
-            response->setReason(str::stream()
-                                << "can see a healthy primary ("
-                                << _rsConfig.getMemberAt(betterPrimary).getHostAndPort()
-                                << ") of equal or greater priority");
+            response
+                ->setReason(str::stream()
+                            << "can see a healthy primary ({}) of equal or greater priority"_format(
+                                   _rsConfig.getMemberAt(betterPrimary).getHostAndPort()));
         } else {
             if (!args.isADryRun()) {
                 _lastVote.setTerm(args.getTerm());
diff --git a/src/mongo/db/repl/topology_coordinator_v1_test.cpp b/src/mongo/db/repl/topology_coordinator_v1_test.cpp
index 5a6da50ee33..54519ab8390 100644
--- a/src/mongo/db/repl/topology_coordinator_v1_test.cpp
+++ b/src/mongo/db/repl/topology_coordinator_v1_test.cpp
@@ -2484,7 +2484,8 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantVotesToTwoDifferentNodesInTheSameTerm) {
     args.initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 1LL << "candidateIndex" << 0LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
@@ -2498,7 +2499,8 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantVotesToTwoDifferentNodesInTheSameTerm) {
         .initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 1LL << "candidateIndex" << 1LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response2;
@@ -2562,7 +2564,7 @@ TEST_F(TopoCoordTest, DryRunVoteRequestShouldNotPreventSubsequentDryRunsForThatT
                                                << "rs0"
                                                << "dryRun" << true << "term" << 1LL
                                                << "candidateIndex" << 0LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
@@ -2578,7 +2580,7 @@ TEST_F(TopoCoordTest, DryRunVoteRequestShouldNotPreventSubsequentDryRunsForThatT
                                                << "rs0"
                                                << "dryRun" << true << "term" << 1LL
                                                << "candidateIndex" << 0LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response2;
@@ -2594,7 +2596,7 @@ TEST_F(TopoCoordTest, DryRunVoteRequestShouldNotPreventSubsequentDryRunsForThatT
                                                << "rs0"
                                                << "dryRun" << false << "term" << 1LL
                                                << "candidateIndex" << 0LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response3;
@@ -2610,7 +2612,7 @@ TEST_F(TopoCoordTest, DryRunVoteRequestShouldNotPreventSubsequentDryRunsForThatT
                                                << "rs0"
                                                << "dryRun" << false << "term" << 1LL
                                                << "candidateIndex" << 0LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response4;
@@ -2640,7 +2642,7 @@ TEST_F(TopoCoordTest, VoteRequestShouldNotPreventDryRunsForThatTerm) {
                                                << "rs0"
                                                << "dryRun" << false << "term" << 1LL
                                                << "candidateIndex" << 0LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
@@ -2656,7 +2658,7 @@ TEST_F(TopoCoordTest, VoteRequestShouldNotPreventDryRunsForThatTerm) {
                                                << "rs0"
                                                << "dryRun" << false << "term" << 1LL
                                                << "candidateIndex" << 0LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response2;
@@ -2685,7 +2687,8 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantVoteWhenReplSetNameDoesNotMatch) {
     args.initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "wrongName"
                                                << "term" << 1LL << "candidateIndex" << 0LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
@@ -2695,10 +2698,10 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantVoteWhenReplSetNameDoesNotMatch) {
     ASSERT_FALSE(response.getVoteGranted());
 }
 
-TEST_F(TopoCoordTest, NodeDoesNotGrantVoteWhenConfigVersionDoesNotMatch) {
+TEST_F(TopoCoordTest, NodeDoesNotGrantVoteWhenConfigVersionIsLower) {
     updateConfig(BSON("_id"
                       << "rs0"
-                      << "version" << 1 << "members"
+                      << "version" << 1 << "term" << 1LL << "members"
                       << BSON_ARRAY(BSON("_id" << 10 << "host"
                                                << "hself")
                                     << BSON("_id" << 20 << "host"
@@ -2713,13 +2716,47 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantVoteWhenConfigVersionDoesNotMatch) {
     args.initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 1LL << "candidateIndex" << 1LL
-                                               << "configVersion" << 0LL << "lastCommittedOp"
+                                               << "configVersion" << 0LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
+                                               << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
+        .transitional_ignore();
+    ReplSetRequestVotesResponse response;
+
+    getTopoCoord().processReplSetRequestVotes(args, &response);
+    ASSERT_EQUALS(
+        "ignoring term of -1 for comparison, candidate's version in config(term, version): (1, 0) "
+        "is lower than mine (1, 1)",
+        response.getReason());
+    ASSERT_FALSE(response.getVoteGranted());
+}
+
+TEST_F(TopoCoordTest, NodeDoesNotGrantVoteWhenConfigTermIsLower) {
+    updateConfig(BSON("_id"
+                      << "rs0"
+                      << "version" << 1 << "term" << 2LL << "members"
+                      << BSON_ARRAY(BSON("_id" << 10 << "host"
+                                               << "hself")
+                                    << BSON("_id" << 20 << "host"
+                                                  << "h2")
+                                    << BSON("_id" << 30 << "host"
+                                                  << "h3"))),
+                 0);
+    setSelfMemberState(MemberState::RS_SECONDARY);
+
+    // lower configTerm
+    ReplSetRequestVotesArgs args;
+    args.initialize(BSON("replSetRequestVotes" << 1 << "setName"
+                                               << "rs0"
+                                               << "term" << 1LL << "candidateIndex" << 1LL
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
 
     getTopoCoord().processReplSetRequestVotes(args, &response);
-    ASSERT_EQUALS("candidate's config version (0) differs from mine (1)", response.getReason());
+    ASSERT_EQUALS("candidate's term in config(term, version): (1, 1) is lower than mine (2, 1)",
+                  response.getReason());
     ASSERT_FALSE(response.getVoteGranted());
 }
 
@@ -2745,7 +2782,8 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantVoteWhenTermIsStale) {
     args.initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 1LL << "candidateIndex" << 1LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
@@ -2775,7 +2813,8 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantVoteWhenOpTimeIsStale) {
     args.initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 3LL << "candidateIndex" << 1LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
@@ -2811,7 +2850,8 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenReplSetNameDoesNotMatch) {
         .initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 1LL << "candidateIndex" << 0LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse responseForRealVote;
@@ -2827,7 +2867,7 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenReplSetNameDoesNotMatch) {
                                                << "wrongName"
                                                << "dryRun" << true << "term" << 2LL
                                                << "candidateIndex" << 0LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
@@ -2838,10 +2878,10 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenReplSetNameDoesNotMatch) {
     ASSERT_FALSE(response.getVoteGranted());
 }
 
-TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenConfigVersionDoesNotMatch) {
+TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenConfigVersionIsLower) {
     updateConfig(BSON("_id"
                       << "rs0"
-                      << "version" << 1 << "members"
+                      << "version" << 1 << "term" << 1LL << "members"
                       << BSON_ARRAY(BSON("_id" << 10 << "host"
                                                << "hself")
                                     << BSON("_id" << 20 << "host"
@@ -2859,7 +2899,8 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenConfigVersionDoesNotMatch) {
         .initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 1LL << "candidateIndex" << 0LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse responseForRealVote;
@@ -2875,13 +2916,16 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenConfigVersionDoesNotMatch) {
                                                << "rs0"
                                                << "dryRun" << true << "term" << 2LL
                                                << "candidateIndex" << 1LL << "configVersion" << 0LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
 
     getTopoCoord().processReplSetRequestVotes(args, &response);
-    ASSERT_EQUALS("candidate's config version (0) differs from mine (1)", response.getReason());
+    ASSERT_EQUALS(
+        "ignoring term of -1 for comparison, candidate's version in config(term, version): (1, 0) "
+        "is lower than mine (1, 1)",
+        response.getReason());
     ASSERT_EQUALS(1, response.getTerm());
     ASSERT_FALSE(response.getVoteGranted());
 }
@@ -2907,7 +2951,8 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenTermIsStale) {
         .initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 1LL << "candidateIndex" << 0LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse responseForRealVote;
@@ -2922,7 +2967,7 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenTermIsStale) {
                                                << "rs0"
                                                << "dryRun" << true << "term" << 0LL
                                                << "candidateIndex" << 1LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
@@ -2933,6 +2978,40 @@ TEST_F(TopoCoordTest, NodeDoesNotGrantDryRunVoteWhenTermIsStale) {
     ASSERT_FALSE(response.getVoteGranted());
 }
 
+TEST_F(TopoCoordTest, NodeGrantsVoteWhenTermIsHigherButConfigVersionIsLower) {
+    updateConfig(BSON("_id"
+                      << "rs0"
+                      << "version" << 2 << "term" << 1LL << "members"
+                      << BSON_ARRAY(BSON("_id" << 10 << "host"
+                                               << "hself")
+                                    << BSON("_id" << 20 << "host"
+                                                  << "h2")
+                                    << BSON("_id" << 30 << "host"
+                                                  << "h3"))),
+                 0);
+    setSelfMemberState(MemberState::RS_SECONDARY);
+
+    // set term to 2
+    ASSERT(TopologyCoordinator::UpdateTermResult::kUpdatedTerm ==
+           getTopoCoord().updateTerm(2, now()));
+
+    // mismatched configVersion
+    ReplSetRequestVotesArgs args;
+    args.initialize(BSON("replSetRequestVotes" << 1 << "setName"
+                                               << "rs0"
+                                               << "term" << 2LL << "candidateIndex" << 1LL
+                                               << "configVersion" << 1LL << "configTerm" << 2LL
+                                               << "lastCommittedOp"
+                                               << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
+        .transitional_ignore();
+    ReplSetRequestVotesResponse response;
+
+    getTopoCoord().processReplSetRequestVotes(args, &response);
+    // Candidates config(t, v) is (2, 1) and our config is (1, 2). Even though the candidate's
+    // config version is lower, we grant our vote because the candidate's config term is higher.
+    ASSERT_TRUE(response.getVoteGranted());
+}
+
 TEST_F(TopoCoordTest, GrantDryRunVoteEvenWhenTermHasBeenSeen) {
     updateConfig(BSON("_id"
                       << "rs0"
@@ -2954,7 +3033,8 @@ TEST_F(TopoCoordTest, GrantDryRunVoteEvenWhenTermHasBeenSeen) {
         .initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 1LL << "candidateIndex" << 0LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse responseForRealVote;
@@ -2970,7 +3050,7 @@ TEST_F(TopoCoordTest, GrantDryRunVoteEvenWhenTermHasBeenSeen) {
                                                << "rs0"
                                                << "dryRun" << true << "term" << 1LL
                                                << "candidateIndex" << 1LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
@@ -3002,7 +3082,8 @@ TEST_F(TopoCoordTest, DoNotGrantDryRunVoteWhenOpTimeIsStale) {
         .initialize(BSON("replSetRequestVotes" << 1 << "setName"
                                                << "rs0"
                                                << "term" << 1LL << "candidateIndex" << 0LL
-                                               << "configVersion" << 1LL << "lastCommittedOp"
+                                               << "configVersion" << 1LL << "configTerm" << 1LL
+                                               << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse responseForRealVote;
@@ -3018,7 +3099,7 @@ TEST_F(TopoCoordTest, DoNotGrantDryRunVoteWhenOpTimeIsStale) {
                                                << "rs0"
                                                << "dryRun" << true << "term" << 3LL
                                                << "candidateIndex" << 1LL << "configVersion" << 1LL
-                                               << "lastCommittedOp"
+                                               << "configTerm" << 1LL << "lastCommittedOp"
                                                << BSON("ts" << Timestamp(10, 0) << "term" << 0LL)))
         .transitional_ignore();
     ReplSetRequestVotesResponse response;
diff --git a/src/mongo/db/repl/vote_requester.cpp b/src/mongo/db/repl/vote_requester.cpp
index ad29d5f5725..fbef232b5b2 100644
--- a/src/mongo/db/repl/vote_requester.cpp
+++ b/src/mongo/db/repl/vote_requester.cpp
@@ -87,6 +87,7 @@ std::vector<RemoteCommandRequest> VoteRequester::Algorithm::getRequests() const
     requestVotesCmdBuilder.append("term", _term);
     requestVotesCmdBuilder.append("candidateIndex", _candidateIndex);
     requestVotesCmdBuilder.append("configVersion", _rsConfig.getConfigVersion());
+    requestVotesCmdBuilder.append("configTerm", _rsConfig.getConfigTerm());
 
     _lastDurableOpTime.append(&requestVotesCmdBuilder, "lastCommittedOp");