When one shard, sole primary node marks potentially failed replica as FAIL instead of PFAIL (#12824)

Fixes issue where a single primary cannot mark a replica as failed in a
single-shard cluster.

src/cluster_legacy.c

@@ -959,7 +959,7 @@ void clusterInit(void) {
     server.cluster->myself = NULL;
     server.cluster->currentEpoch = 0;
     server.cluster->state = CLUSTER_FAIL;
-    server.cluster->size = 1;
+    server.cluster->size = 0;
     server.cluster->todo_before_sleep = 0;
     server.cluster->nodes = dictCreate(&clusterNodesDictType);
     server.cluster->shards = dictCreate(&clusterSdsToListType);
@@ -4691,10 +4691,13 @@ void clusterCron(void) {
             /* Timeout reached. Set the node as possibly failing if it is
              * not already in this state. */
             if (!(node->flags & (CLUSTER_NODE_PFAIL|CLUSTER_NODE_FAIL))) {
-                serverLog(LL_DEBUG,"*** NODE %.40s possibly failing",
-                    node->name);
                 node->flags |= CLUSTER_NODE_PFAIL;
                 update_state = 1;
+                if (clusterNodeIsMaster(myself) && server.cluster->size == 1) {
+                    markNodeAsFailingIfNeeded(node);                    
+                } else {
+                    serverLog(LL_DEBUG,"*** NODE %.40s possibly failing", node->name);
+                }
             }
         }
     }

tests/support/cluster_util.tcl

@@ -199,3 +199,30 @@ proc are_hostnames_propagated {match_string} {
     }
     return 1
 }
+
+proc wait_node_marked_fail {ref_node_index instance_id_to_check} {
+    wait_for_condition 1000 50 {
+        [check_cluster_node_mark fail $ref_node_index $instance_id_to_check]
+    } else {
+        fail "Replica node never marked as FAIL ('fail')"
+    }
+}
+
+proc wait_node_marked_pfail {ref_node_index instance_id_to_check} {
+    wait_for_condition 1000 50 {
+        [check_cluster_node_mark fail\? $ref_node_index $instance_id_to_check]
+    } else {
+        fail "Replica node never marked as PFAIL ('fail?')"
+    }
+}
+
+proc check_cluster_node_mark {flag ref_node_index instance_id_to_check} {
+    set nodes [get_cluster_nodes $ref_node_index]
+
+    foreach n $nodes {
+        if {[dict get $n id] eq $instance_id_to_check} {
+            return [cluster_has_flag $n $flag]
+        }
+    }
+    fail "Unable to find instance id in cluster nodes. ID: $instance_id_to_check"
+}

tests/test_helper.tcl

@@ -104,6 +104,7 @@ set ::all_tests {
     unit/cluster/slot-ownership
     unit/cluster/links
     unit/cluster/cluster-response-tls
+    unit/cluster/failure-marking
 }
 # Index to the next test to run in the ::all_tests list.
 set ::next_test 0

tests/unit/cluster/failure-marking.tcl

@@ -0,0 +1,53 @@
+# Test a single primary can mark replica as `fail`
+start_cluster 1 1 {tags {external:skip cluster}} {
+
+    test "Verify that single primary marks replica as failed" {
+        set primary [srv -0 client]
+
+        set replica1 [srv -1 client]
+        set replica1_pid [srv -1 pid]
+        set replica1_instance_id [dict get [cluster_get_myself 1] id]
+
+        assert {[lindex [$primary role] 0] eq {master}}
+        assert {[lindex [$replica1 role] 0] eq {slave}}
+
+        wait_for_sync $replica1
+
+        pause_process $replica1_pid
+
+        wait_node_marked_fail 0 $replica1_instance_id
+    }
+}
+
+# Test multiple primaries wait for a quorum and then mark a replica as `fail`
+start_cluster 2 1 {tags {external:skip cluster}} {
+
+    test "Verify that multiple primaries mark replica as failed" {
+        set primary1 [srv -0 client]
+
+        set primary2 [srv -1 client]
+        set primary2_pid [srv -1 pid]
+
+        set replica1 [srv -2 client]
+        set replica1_pid [srv -2 pid]
+        set replica1_instance_id [dict get [cluster_get_myself 2] id]
+
+        assert {[lindex [$primary1 role] 0] eq {master}}
+        assert {[lindex [$primary2 role] 0] eq {master}}
+        assert {[lindex [$replica1 role] 0] eq {slave}}
+
+        wait_for_sync $replica1
+
+        pause_process $replica1_pid
+
+        # Pause other primary to allow time for pfail flag to appear
+        pause_process $primary2_pid
+
+        wait_node_marked_pfail 0 $replica1_instance_id
+
+        # Resume other primary and wait for to show replica as failed
+        resume_process $primary2_pid
+
+        wait_node_marked_fail 0 $replica1_instance_id
+    }
+}