Fix missing replication link re-connection when primary's IP/port is …

…updated in `clusterProcessGossipSection` (#965)

`clusterProcessGossipSection` currently doesn't trigger a check and call `replicationSetPrimary` when `myself`'s primary node’s IP/port is updated. This fix ensures that after every node address update, `replicationSetPrimary` is called if the updated node is `myself`'s primary. This prevents missed updates and ensures that replicas reconnect properly to maintain their replication link with the primary.

Signed-off-by: Ping Xie <pingxie@google.com>

src/cluster_legacy.c

@@ -2275,6 +2275,23 @@ void clusterProcessGossipSection(clusterMsg *hdr, clusterLink *link) {
                 node->tls_port = msg_tls_port;
                 node->cport = ntohs(g->cport);
                 node->flags &= ~CLUSTER_NODE_NOADDR;
+
+                serverLog(LL_NOTICE, "Address updated for node %.40s (%s), now %s:%d", node->name, node->human_nodename,
+                          node->ip, getNodeDefaultClientPort(node));
+
+                /* Check if this is our primary and we have to change the
+                 * replication target as well.
+                 *
+                 * This is needed in case the check in nodeUpdateAddressIfNeeded
+                 * failed due to a race condition. For example, if the replica just
+                 * received a packet from another node that contains new address
+                 * about the primary, we will update primary node address in here,
+                 * when the replica receive the packet from the primary, the check
+                 * in nodeUpdateAddressIfNeeded will fail since the address has been
+                 * updated correctly, and we will not have the opportunity to call
+                 * replicationSetPrimary and update the primary host. */
+                if (nodeIsReplica(myself) && myself->replicaof == node)
+                    replicationSetPrimary(node->ip, getNodeDefaultReplicationPort(node), 0);
             }
         } else if (!node) {
             /* If it's not in NOADDR state and we don't have it, we