[cluster-bus] Send a MEET packet to a node if there is no inbound link

In some cases, when meeting a new node, if the handshake times out, we can end up with an inconsistent view of the cluster where the new node knows about all the nodes in the cluster, but the cluster does not know about this new node (or vice versa). To detect this inconsistency, we now check if a node has an outbound link but no inbound link, in this case it probably means this node does not know us. In this case we (re-)send a MEET packet to this node to do a new handshake with it. Signed-off-by: Pierre Turin <[email protected]>
valkey-io · Nov 14, 2024 · 6b64975 · 6b64975
1 parent 32f7541
commit 6b64975
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Showing 4 changed files with 214 additions and 13 deletions.
diff --git a/src/cluster_legacy.c b/src/cluster_legacy.c
@@ -1335,6 +1335,10 @@ clusterLink *createClusterLink(clusterNode *node) {
  * with this link will have the 'link' field set to NULL. */
 void freeClusterLink(clusterLink *link) {
     serverAssert(link != NULL);
+    serverLog(LL_DEBUG, "Freeing cluster link for node: %.40s:%s",
+              link->node ? link->node->name : "<unknown>",
+              link->inbound ? "inbound" : "outbound");
+
     if (link->conn) {
         connClose(link->conn);
         link->conn = NULL;
@@ -1350,6 +1354,7 @@ void freeClusterLink(clusterLink *link) {
         } else if (link->node->inbound_link == link) {
             serverAssert(link->inbound);
             link->node->inbound_link = NULL;
+            link->node->inbound_link_freed_time = mstime();
         }
     }
     zfree(link);
@@ -1489,6 +1494,7 @@ clusterNode *createClusterNode(char *nodename, int flags) {
     node->fail_time = 0;
     node->link = NULL;
     node->inbound_link = NULL;
+    node->inbound_link_freed_time = node->ctime;
     memset(node->ip, 0, sizeof(node->ip));
     node->announce_client_ipv4 = sdsempty();
     node->announce_client_ipv6 = sdsempty();
@@ -1695,6 +1701,9 @@ void clusterAddNode(clusterNode *node) {
  *    it is a replica node.
  */
 void clusterDelNode(clusterNode *delnode) {
+    serverAssert(delnode != NULL);
+    serverLog(LL_DEBUG, "Deleting node %s from cluster view", delnode->name);
+
     int j;
     dictIterator *di;
     dictEntry *de;
@@ -2077,7 +2086,7 @@ void clearNodeFailureIfNeeded(clusterNode *node) {
 /* Return 1 if we already have a node in HANDSHAKE state matching the
  * specified ip address and port number. This function is used in order to
  * avoid adding a new handshake node for the same address multiple times. */
-int clusterHandshakeInProgress(char *ip, int port, int cport) {
+static int clusterHandshakeInProgress(char *ip, int port, int cport) {
     dictIterator *di;
     dictEntry *de;
 
@@ -2099,7 +2108,7 @@ int clusterHandshakeInProgress(char *ip, int port, int cport) {
  *
  * EAGAIN - There is already a handshake in progress for this address.
  * EINVAL - IP or port are not valid. */
-int clusterStartHandshake(char *ip, int port, int cport) {
+static int clusterStartHandshake(char *ip, int port, int cport) {
     clusterNode *n;
     char norm_ip[NET_IP_STR_LEN];
     struct sockaddr_storage sa;
@@ -3224,12 +3233,12 @@ int clusterProcessPacket(clusterLink *link) {
             setClusterNodeToInboundClusterLink(node, link);
             clusterAddNode(node);
             clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
-        }
 
-        /* If this is a MEET packet from an unknown node, we still process
-         * the gossip section here since we have to trust the sender because
-         * of the message type. */
-        if (!sender && type == CLUSTERMSG_TYPE_MEET) clusterProcessGossipSection(hdr, link);
+            /* If this is a MEET packet from an unknown node, we still process
+             * the gossip section here since we have to trust the sender because
+             * of the message type. */
+            clusterProcessGossipSection(hdr, link);
+        }
 
         /* Anyway reply with a PONG */
         clusterSendPing(link, CLUSTERMSG_TYPE_PONG);
@@ -3240,7 +3249,7 @@ int clusterProcessPacket(clusterLink *link) {
         serverLog(LL_DEBUG, "%s packet received: %.40s", clusterGetMessageTypeString(type),
                   link->node ? link->node->name : "NULL");
 
-        if (sender && (sender->flags & CLUSTER_NODE_MEET)) {
+        if (sender && nodeIsMeeting(sender)) {
             /* Once we get a response for MEET from the sender, we can stop sending more MEET. */
             sender->flags &= ~CLUSTER_NODE_MEET;
             serverLog(LL_NOTICE, "Successfully completed handshake with %.40s (%s)", sender->name,
@@ -3665,7 +3674,7 @@ void clusterLinkConnectHandler(connection *conn) {
      * of a PING one, to force the receiver to add us in its node
      * table. */
     mstime_t old_ping_sent = node->ping_sent;
-    clusterSendPing(link, node->flags & CLUSTER_NODE_MEET ? CLUSTERMSG_TYPE_MEET : CLUSTERMSG_TYPE_PING);
+    clusterSendPing(link, nodeIsMeeting(node) ? CLUSTERMSG_TYPE_MEET : CLUSTERMSG_TYPE_PING);
     if (old_ping_sent) {
         /* If there was an active ping before the link was
          * disconnected, we want to restore the ping time, otherwise
@@ -3685,6 +3694,9 @@ void clusterLinkConnectHandler(connection *conn) {
      */
 
     serverLog(LL_DEBUG, "Connecting with Node %.40s at %s:%d", node->name, node->ip, node->cport);
+    if (nodeIsMeeting(node)) {
+        serverLog(LL_DEBUG, "Sending MEET packet on connection to node %.40s", node->name);
+    }
 }
 
 /* Performs sanity check on the message signature and length depending on the type. */
@@ -3744,7 +3756,9 @@ void clusterReadHandler(connection *conn) {
 
         if (nread <= 0) {
             /* I/O error... */
-            serverLog(LL_DEBUG, "I/O error reading from node link: %s",
+            serverLog(LL_DEBUG, "I/O error reading from node link (%.40s:%s): %s",
+                      link->node ? link->node->name : "<unknown>",
+                      link->inbound ? "inbound" : "outbound",
                       (nread == 0) ? "connection closed" : connGetLastError(conn));
             handleLinkIOError(link);
             return;
@@ -4909,9 +4923,21 @@ static int clusterNodeCronHandleReconnect(clusterNode *node, mstime_t handshake_
     /* A Node in HANDSHAKE state has a limited lifespan equal to the
      * configured node timeout. */
     if (nodeInHandshake(node) && now - node->ctime > handshake_timeout) {
+        serverLog(LL_NOTICE, "Clusterbus handshake timeout [%s]:%d after a timeout of %lld",
+                  node->ip, node->cport, handshake_timeout);
         clusterDelNode(node);
         return 1;
     }
+    if (node->link != NULL && node->inbound_link == NULL &&
+        !nodeInHandshake(node) && !nodeIsMeeting(node) && !nodeTimedOut(node) &&
+        now - node->inbound_link_freed_time > handshake_timeout) {
+        /* Node has an outbound link, but no inbound link for more than the handshake timeout.
+         * This probably means this node does not know us yet, wherease we know it.
+         * So we send it a MEET packet to do a handshake with it and correct the inconsistent cluster view. */
+        node->flags |= CLUSTER_NODE_MEET;
+        serverLog(LL_NOTICE, "Sending MEET packet to node %.40s because there is no inbound link for it", node->name);
+        clusterSendPing(node->link, CLUSTERMSG_TYPE_MEET);
+    }
 
     if (node->link == NULL) {
         clusterLink *link = createClusterLink(node);
@@ -4934,6 +4960,7 @@ static int clusterNodeCronHandleReconnect(clusterNode *node, mstime_t handshake_
             return 0;
         }
     }
+
     return 0;
 }
 

diff --git a/src/cluster_legacy.h b/src/cluster_legacy.h
@@ -60,6 +60,7 @@ typedef struct clusterLink {
 #define nodeIsPrimary(n) ((n)->flags & CLUSTER_NODE_PRIMARY)
 #define nodeIsReplica(n) ((n)->flags & CLUSTER_NODE_REPLICA)
 #define nodeInHandshake(n) ((n)->flags & CLUSTER_NODE_HANDSHAKE)
+#define nodeIsMeeting(n) ((n)->flags & CLUSTER_NODE_MEET)
 #define nodeHasAddr(n) (!((n)->flags & CLUSTER_NODE_NOADDR))
 #define nodeTimedOut(n) ((n)->flags & CLUSTER_NODE_PFAIL)
 #define nodeFailed(n) ((n)->flags & CLUSTER_NODE_FAIL)
@@ -341,6 +342,8 @@ struct _clusterNode {
     mstime_t voted_time;                    /* Last time we voted for a replica of this primary */
     mstime_t repl_offset_time;              /* Unix time we received offset for this node */
     mstime_t orphaned_time;                 /* Starting time of orphaned primary condition */
+    mstime_t inbound_link_freed_time;       /* Last time we freed the inbound link for this node.
+                                               If it was never freed, it is the same as ctime */
     long long repl_offset;                  /* Last known repl offset for this node. */
     char ip[NET_IP_STR_LEN];                /* Latest known IP address of this node */
     sds announce_client_ipv4;               /* IPv4 for clients only. */

diff --git a/tests/support/cluster_util.tcl b/tests/support/cluster_util.tcl
@@ -322,6 +322,15 @@ proc get_cluster_nodes {id {status "*"}} {
     return $nodes
 }
 
+# Returns the parsed myself node entry as a dictionary.
+proc get_myself id {
+    set nodes [get_cluster_nodes $id]
+    foreach n $nodes {
+        if {[cluster_has_flag $n myself]} {return $n}
+    }
+    return {}
+}
+
 # Returns 1 if no node knows node_id, 0 if any node knows it.
 proc node_is_forgotten {node_id} {
     for {set j 0} {$j < [llength $::servers]} {incr j} {

diff --git a/tests/unit/cluster/cluster-reliable-meet.tcl b/tests/unit/cluster/cluster-reliable-meet.tcl
@@ -3,6 +3,12 @@ set old_singledb $::singledb
 set ::singledb 1
 
 tags {tls:skip external:skip cluster} {
+    set CLUSTER_PACKET_TYPE_PING 0
+    set CLUSTER_PACKET_TYPE_PONG 1
+    set CLUSTER_PACKET_TYPE_MEET 2
+    set CLUSTER_PACKET_TYPE_NONE -1
+    set CLUSTER_PACKET_TYPE_ALL -2
+
     set base_conf [list cluster-enabled yes]
     start_multiple_servers 2 [list overrides $base_conf] {
         test "Cluster nodes are reachable" {
@@ -22,9 +28,6 @@ tags {tls:skip external:skip cluster} {
             wait_for_cluster_state fail
         }
 
-        set CLUSTER_PACKET_TYPE_MEET 2
-        set CLUSTER_PACKET_TYPE_NONE -1
-
         test "Cluster nodes haven't met each other" {
             assert {[llength [get_cluster_nodes 1]] == 1}
             assert {[llength [get_cluster_nodes 0]] == 1}
@@ -75,3 +78,162 @@ tags {tls:skip external:skip cluster} {
 
 set ::singledb $old_singledb
 
+proc cluster_get_first_node_in_handshake id {
+    set nodes [get_cluster_nodes $id]
+    foreach n $nodes {
+        if {[cluster_has_flag $n handshake]} {
+            return [dict get $n id]
+        }
+    }
+    return {}
+}
+
+start_cluster 2 0 {tags {external:skip cluster} overrides {cluster-node-timeout 4000 cluster-replica-no-failover yes}} {
+    set CLUSTER_PACKET_TYPE_PING 0
+    set CLUSTER_PACKET_TYPE_PONG 1
+    set CLUSTER_PACKET_TYPE_MEET 2
+    set CLUSTER_PACKET_TYPE_NONE -1
+    set CLUSTER_PACKET_TYPE_ALL -2
+
+    test "Handshake eventually succeeds after node handshake timeout on both sides with inconsistent view of the cluster" {
+        set cluster_port [find_available_port $::baseport $::portcount]
+        start_server [list overrides [list cluster-enabled yes cluster-node-timeout 4000 cluster-port $cluster_port]] {
+            # In this test we will trigger a handshake timeout on both sides of the handshake.
+            # Node 1 and 2 already know each other, then we make node 1 meet node 0:
+            #
+            # Node 1 -- MEET -> Node 0 [Node 0 might learn about Node 2 from the gossip section of the msg]
+            # Node 1 <- PONG -- Node 0 [we drop this message, so Node 1 will eventually mark the handshake as timed out]
+            # Node 1 <- PING -- Node 0 [we drop this message, so Node 1 will never send a PONG and Node 0 will eventually mark the handshake as timed out]
+            #
+            # After the handshake is timed out, we allow all cluster bus messages to go through.
+            # Eventually Node 0 should send a MEET packet to the other nodes to complete the handshake.
+
+            # Drop all cluster bus messages
+            R 1 DEBUG DROP-CLUSTER-PACKET-FILTER $CLUSTER_PACKET_TYPE_ALL
+            # Drop MEET cluster bus messages, so that Node 0 cannot start a handshake with Node 2.
+            R 2 DEBUG DROP-CLUSTER-PACKET-FILTER $CLUSTER_PACKET_TYPE_MEET
+
+            R 1 CLUSTER MEET [srv 0 host] [srv 0 port] $cluster_port
+
+            # We want Node 0 to learn about Node 2 through the gossip section of the MEET message
+            set meet_retry 0
+            set node2_id [dict get [get_myself 2] id]
+            while {[cluster_get_node_by_id 0 $node2_id] eq {}} {
+                if {$meet_retry == 10} {
+                    error "assertion: Retried to meet Node 0 too many times"
+                }
+                # If Node 0 doesn't know about Node 1 & 2, it means Node 1 did not gossip about node 2 in its MEET message.
+                # So we kill the outbound link from Node 1 to Node 0, to force a reconnect and a re-send of the MEET message.
+                after 100
+                # Since we are in handshake, we use a randomly generated ID we have to find
+                R 1 DEBUG CLUSTERLINK KILL ALL [cluster_get_first_node_in_handshake 1]
+                incr meet_retry 1
+            }
+
+            # Wait for Node 1's handshake to timeout
+            wait_for_condition 50 100 {
+                [cluster_get_first_node_in_handshake 1] eq {}
+            } else {
+                fail "Node 1 never exited handshake state"
+            }
+
+            # Wait for Node 0's handshake to timeout
+            wait_for_condition 50 100 {
+                [cluster_get_first_node_in_handshake 1] eq {}
+            } else {
+                fail "Node 0 never exited handshake state"
+            }
+
+            # At this point Node 0 knows Node 1 & 2 through the gossip, but they don't know Node 0.
+            wait_for_condition 50 100 {
+                [llength [R 0 CLUSTER NODES]] == 25 &&
+                [llength [R 1 CLUSTER NODES]] == 18 &&
+                [llength [R 2 CLUSTER NODES]] == 18
+            } else {
+                fail "Unexpected CLUSTER NODES output, nodes 1 & 2 should not know node 0."
+            }
+
+            # Allow all messages to go through again
+            R 1 DEBUG DROP-CLUSTER-PACKET-FILTER $CLUSTER_PACKET_TYPE_NONE
+            R 2 DEBUG DROP-CLUSTER-PACKET-FILTER $CLUSTER_PACKET_TYPE_NONE
+
+            # Now Node 0 will send a MEET packet to Node 1 & 2 since it has an outbound link to these nodes but no inblound link.
+            # Handshake should now complete successfully.
+            wait_for_condition 50 200 {
+                [llength [R 0 CLUSTER NODES]] == 26 &&
+                [llength [R 1 CLUSTER NODES]] == 26 &&
+                [llength [R 2 CLUSTER NODES]] == 26
+            } else {
+                fail "Unexpected CLUSTER NODES output, all nodes should know each other."
+            }
+        } ;# stop Node 0
+    } ;# test
+} ;# stop cluster
+
+start_cluster 2 0 {tags {external:skip cluster} overrides {cluster-node-timeout 4000 cluster-replica-no-failover yes}} {
+    set CLUSTER_PACKET_TYPE_PING 0
+    set CLUSTER_PACKET_TYPE_PONG 1
+    set CLUSTER_PACKET_TYPE_MEET 2
+    set CLUSTER_PACKET_TYPE_NONE -1
+    set CLUSTER_PACKET_TYPE_ALL -2
+
+    test "Handshake eventually succeeds after node handshake timeout on one side with inconsistent view of the cluster" {
+        set cluster_port [find_available_port $::baseport $::portcount]
+        start_server [list overrides [list cluster-enabled yes cluster-node-timeout 4000 cluster-port $cluster_port]] {
+            # In this test we will trigger a handshake timeout on one side of the handshake.
+            # Node 1 and 2 already know each other, then we make node 0 meet node 1:
+            #
+            # Node 0 -- MEET -> Node 1
+            # Node 0 <- PONG -- Node 1
+            # Node 0 <- PING -- Node 1 [Node 0 will mark the handshake as successful]
+            # Node 0 -- PONG -> Node 1 [we drop this message, so node 1 will eventually mark the handshake as timed out]
+            #
+            # After the handshake is timed out, we allow all cluster bus messages to go through.
+            # Eventually Node 0 should send a MEET packet to the other nodes to complete the handshake.
+
+            # Drop PONG messages
+            R 1 DEBUG DROP-CLUSTER-PACKET-FILTER $CLUSTER_PACKET_TYPE_PONG
+            # Drop MEET cluster bus messages, so that Node 0 cannot start a handshake with Node 2.
+            R 2 DEBUG DROP-CLUSTER-PACKET-FILTER $CLUSTER_PACKET_TYPE_MEET
+
+            # Node 0 meets node 1
+            R 0 CLUSTER MEET [srv -1 host] [srv -1 port]
+
+            # Wait for node 0 to know about the other nodes in the cluster
+            wait_for_condition 50 100 {
+                [llength [R 0 CLUSTER NODES]] == 26
+            } else {
+                fail "Node 0 never learned about node 1 and 2"
+            }
+            # At this point, node 0 learned about the other nodes in the cluster from meeting node 1.
+            wait_for_condition 50 100 {
+                [cluster_get_first_node_in_handshake 0] eq {}
+            } else {
+                fail "Node 1 never exited handshake state"
+            }
+            # At this point, from node 0 point of view, the handshake with node 1 succeeded.
+
+            wait_for_condition 50 100 {
+                [cluster_get_first_node_in_handshake 1] eq {}
+            } else {
+                fail "Node 1 never exited handshake state"
+            }
+            assert {[llength [R 1 CLUSTER NODES]] == 18}
+            # At this point, from node 1 point of view, the handshake with node 0 timed out.
+
+            # Allow all messages
+            R 1 DEBUG DROP-CLUSTER-PACKET-FILTER $CLUSTER_PACKET_TYPE_NONE
+            R 2 DEBUG DROP-CLUSTER-PACKET-FILTER $CLUSTER_PACKET_TYPE_NONE
+
+            # Now Node 0 will send a MEET packet to Node 1 & 2 since it has an outbound link to these nodes but no inblound link.
+            # Handshake should now complete successfully.
+            wait_for_condition 50 200 {
+                [llength [R 0 CLUSTER NODES]] == 26 &&
+                [llength [R 1 CLUSTER NODES]] == 26 &&
+                [llength [R 2 CLUSTER NODES]] == 26
+            } else {
+                fail "Unexpected CLUSTER NODES output, all nodes should know each other."
+            }
+        } ;# stop Node 0
+    } ;# test
+} ;# stop cluster