SERVER-34465 Add a testing parameter to choose a permanent sync source

2 files changed, 77 insertions, 0 deletions

diff --git a/jstests/replsets/force_sync_source_candidate.js b/jstests/replsets/force_sync_source_candidate.js
new file mode 100644
index 00000000000..4be7b3bb668
--- /dev/null
+++ b/jstests/replsets/force_sync_source_candidate.js
@@ -0,0 +1,40 @@
+/*
+ * Tests that the 'forceSyncSourceCandidate' failpoint correctly forces a sync source.
+ *
+ * @tags: [requires_replication]
+ */
+
+(function() {
+    "use strict";
+
+    const failpointName = "forceSyncSourceCandidate";
+
+    const rst = new ReplSetTest({
+        nodes:
+            [{}, {rsConfig: {priority: 0}}, {rsConfig: {priority: 0}}, {rsConfig: {priority: 0}}],
+        // Allow many initial sync attempts. Initial sync may fail if the sync source does not have
+        // an oplog yet because it has not conducted its own initial sync yet.
+        // We turn on the noop writer to encourage successful sync source selection.
+        nodeOptions: {setParameter: {numInitialSyncAttempts: 100, writePeriodicNoops: true}}
+    });
+    const nodes = rst.startSet();
+
+    function setFailPoint(node, syncSource) {
+        const dataObj = {hostAndPort: syncSource.host};
+        assert.commandWorked(node.adminCommand(
+            {configureFailPoint: failpointName, mode: "alwaysOn", data: dataObj}));
+    }
+
+    setFailPoint(nodes[1], nodes[0]);
+    setFailPoint(nodes[2], nodes[1]);
+    setFailPoint(nodes[3], nodes[2]);
+
+    rst.initiate();
+    const primary = rst.getPrimary();
+
+    rst.awaitSyncSource(nodes[1], nodes[0]);
+    rst.awaitSyncSource(nodes[2], nodes[1]);
+    rst.awaitSyncSource(nodes[3], nodes[2]);
+
+    rst.stopSet();
+})();
diff --git a/src/mongo/db/repl/topology_coordinator.cpp b/src/mongo/db/repl/topology_coordinator.cpp
index fe52da99b42..5ca660a2012 100644
--- a/src/mongo/db/repl/topology_coordinator.cpp
+++ b/src/mongo/db/repl/topology_coordinator.cpp
@@ -63,6 +63,8 @@
 namespace mongo {
 namespace repl {
 
+MONGO_FP_DECLARE(forceSyncSourceCandidate);
+
 const Seconds TopologyCoordinator::VoteLease::leaseTime = Seconds(30);
 
 // Controls how caught up in replication a secondary with higher priority than the current primary
@@ -205,6 +207,41 @@ HostAndPort TopologyCoordinator::chooseNewSyncSource(Date_t now,
         return HostAndPort();
     }
 
+    MONGO_FAIL_POINT_BLOCK(forceSyncSourceCandidate, customArgs) {
+        const auto& data = customArgs.getData();
+        const auto hostAndPortElem = data["hostAndPort"];
+        if (!hostAndPortElem) {
+            severe() << "'forceSyncSoureCandidate' parameter set with invalid host and port: "
+                     << data;
+            fassertFailed(50835);
+        }
+
+        const auto hostAndPort = HostAndPort(hostAndPortElem.checkAndGetStringData());
+        const int syncSourceIndex = _rsConfig.findMemberIndexByHostAndPort(hostAndPort);
+        if (syncSourceIndex < 0) {
+            log() << "'forceSyncSourceCandidate' failed due to host and port not in "
+                     "replica set config: "
+                  << hostAndPort.toString();
+            fassertFailed(50836);
+        }
+
+
+        if (_memberIsBlacklisted(_rsConfig.getMemberAt(syncSourceIndex), now)) {
+            log() << "Cannot select a sync source because forced candidate is blacklisted: "
+                  << hostAndPort.toString();
+            _syncSource = HostAndPort();
+            return _syncSource;
+        }
+
+        _syncSource = _rsConfig.getMemberAt(syncSourceIndex).getHostAndPort();
+        log() << "choosing sync source candidate due to 'forceSyncSourceCandidate' parameter: "
+              << _syncSource;
+        std::string msg(str::stream() << "syncing from: " << _syncSource.toString()
+                                      << " by 'forceSyncSourceCandidate' parameter");
+        setMyHeartbeatMessage(now, msg);
+        return _syncSource;
+    }
+
     // if we have a target we've requested to sync from, use it
     if (_forceSyncSourceIndex != -1) {
         invariant(_forceSyncSourceIndex < _rsConfig.getNumMembers());