SERVER-43904: Filter unelectable nodes during election handoff

(cherry picked from commit bf614cb57059c74830633855e28b3f4677cd4f8d)

3 files changed, 31 insertions, 6 deletions

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..2e773d4c471
--- /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 6728a245bbe..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.
@@ -27,11 +27,8 @@ var testMoveChunkWithSession = function(
     checkRetryResultFunc(result, assert.commandWorked(testDB.runCommand(cmdObj)));
     checkDocumentsFunc(coll);
 
-    try {
-        st.rs1.getPrimary().adminCommand({replSetStepDown: 60, secondaryCatchUpPeriodSecs: 30});
-    } catch (excep) {
-        print('Expected exception due to step down: ' + tojson(excep));
-    }
+    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/topology_coordinator.cpp b/src/mongo/db/repl/topology_coordinator.cpp
index 506b0928416..7742c42cdb5 100644
--- a/src/mongo/db/repl/topology_coordinator.cpp
+++ b/src/mongo/db/repl/topology_coordinator.cpp
@@ -928,6 +928,9 @@ Status TopologyCoordinator::prepareHeartbeatResponseV1(Date_t now,
         return Status::OK();
     }
 
+    response->setElectable(
+        !_getMyUnelectableReason(now, StartElectionReasonEnum::kElectionTimeout));
+
     const long long v = _rsConfig.getConfigVersion();
     response->setConfigVersion(v);
     // Deliver new config if caller's version is older than ours