[NET-3865] [Supportability] Additional Information in the output of 'consul operator raft list-peers'

.changelog/17582.txt

@@ -0,0 +1,3 @@
+```release-note:feature
+cli: `consul operator raft list-peers` command shows the number of commits each follower is trailing the leader by to aid in troubleshooting.
+```

agent/consul/operator_raft_endpoint.go

@@ -48,6 +48,12 @@ func (op *Operator) RaftGetConfiguration(args *structs.DCSpecificRequest, reply
 		serverMap[raft.ServerAddress(addr)] = member
 	}
 
+	serverIDLastIndexMap := make(map[raft.ServerID]uint64)
+
+	for _, serverState := range op.srv.autopilot.GetState().Servers {
+		serverIDLastIndexMap[serverState.Server.ID] = serverState.Stats.LastIndex
+	}
+
 	// Fill out the reply.
 	leader := op.srv.raft.Leader()
 	reply.Index = future.Index()
@@ -66,6 +72,7 @@ func (op *Operator) RaftGetConfiguration(args *structs.DCSpecificRequest, reply
 			Leader:          server.Address == leader,
 			Voter:           server.Suffrage == raft.Voter,
 			ProtocolVersion: raftProtocolVersion,
+			LastIndex:       serverIDLastIndexMap[server.ID],
 		}
 		reply.Servers = append(reply.Servers, entry)
 	}

agent/consul/operator_raft_endpoint_test.go

@@ -50,6 +50,13 @@ func TestOperator_RaftGetConfiguration(t *testing.T) {
 	if len(future.Configuration().Servers) != 1 {
 		t.Fatalf("bad: %v", future.Configuration().Servers)
 	}
+
+	serverIDLastIndexMap := make(map[raft.ServerID]uint64)
+
+	for _, serverState := range s1.autopilot.GetState().Servers {
+		serverIDLastIndexMap[serverState.Server.ID] = serverState.Stats.LastIndex
+	}
+
 	me := future.Configuration().Servers[0]
 	expected := structs.RaftConfigurationResponse{
 		Servers: []*structs.RaftServer{
@@ -60,6 +67,7 @@ func TestOperator_RaftGetConfiguration(t *testing.T) {
 				Leader:          true,
 				Voter:           true,
 				ProtocolVersion: "3",
+				LastIndex:       serverIDLastIndexMap[me.ID],
 			},
 		},
 		Index: future.Index(),
@@ -113,6 +121,10 @@ func TestOperator_RaftGetConfiguration_ACLDeny(t *testing.T) {
 	if len(future.Configuration().Servers) != 1 {
 		t.Fatalf("bad: %v", future.Configuration().Servers)
 	}
+	serverIDLastIndexMap := make(map[raft.ServerID]uint64)
+	for _, serverState := range s1.autopilot.GetState().Servers {
+		serverIDLastIndexMap[serverState.Server.ID] = serverState.Stats.LastIndex
+	}
 	me := future.Configuration().Servers[0]
 	expected := structs.RaftConfigurationResponse{
 		Servers: []*structs.RaftServer{
@@ -123,6 +135,7 @@ func TestOperator_RaftGetConfiguration_ACLDeny(t *testing.T) {
 				Leader:          true,
 				Voter:           true,
 				ProtocolVersion: "3",
+				LastIndex:       serverIDLastIndexMap[me.ID],
 			},
 		},
 		Index: future.Index(),

agent/structs/operator.go

@@ -34,6 +34,9 @@ type RaftServer struct {
 	// it's a non-voting server, which will be added in a future release of
 	// Consul.
 	Voter bool
+
+	// LastIndex is the last log index this server has a record of in its Raft log.
+	LastIndex uint64
 }
 
 // RaftConfigurationResponse is returned when querying for the current Raft

api/operator_raft.go

@@ -28,6 +28,9 @@ type RaftServer struct {
 	// it's a non-voting server, which will be added in a future release of
 	// Consul.
 	Voter bool
+
+	// LastIndex is the last log index this server has a record of in its Raft log.
+	LastIndex uint64
 }
 
 // RaftConfiguration is returned when querying for the current Raft configuration.

command/operator/raft/listpeers/operator_raft_list.go

@@ -70,8 +70,24 @@ func raftListPeers(client *api.Client, stale bool) (string, error) {
 		return "", fmt.Errorf("Failed to retrieve raft configuration: %v", err)
 	}
 
+	leaderLastCommitIndex := uint64(0)
+	serverIdLastIndexMap := make(map[string]uint64)
+
+	for _, raftServer := range reply.Servers {
+		serverIdLastIndexMap[raftServer.ID] = raftServer.LastIndex
+	}
+
+	for _, s := range reply.Servers {
+		if s.Leader {
+			lastIndex, ok := serverIdLastIndexMap[s.ID]
+			if ok {
+				leaderLastCommitIndex = lastIndex
+			}
+		}
+	}
+
 	// Format it as a nice table.
-	result := []string{"Node\x1fID\x1fAddress\x1fState\x1fVoter\x1fRaftProtocol"}
+	result := []string{"Node\x1fID\x1fAddress\x1fState\x1fVoter\x1fRaftProtocol\x1fCommit Index\x1fTrails Leader By"}
 	for _, s := range reply.Servers {
 		raftProtocol := s.ProtocolVersion
 
@@ -82,8 +98,20 @@ func raftListPeers(client *api.Client, stale bool) (string, error) {
 		if s.Leader {
 			state = "leader"
 		}
-		result = append(result, fmt.Sprintf("%s\x1f%s\x1f%s\x1f%s\x1f%v\x1f%s",
-			s.Node, s.ID, s.Address, state, s.Voter, raftProtocol))
+
+		trailsLeaderByText := "-"
+		serverLastIndex, ok := serverIdLastIndexMap[s.ID]
+		if ok {
+			trailsLeaderBy := leaderLastCommitIndex - serverLastIndex
+			trailsLeaderByText = fmt.Sprintf("%d commits", trailsLeaderBy)
+			if s.Leader {
+				trailsLeaderByText = "-"
+			} else if trailsLeaderBy == 1 {
+				trailsLeaderByText = fmt.Sprintf("%d commit", trailsLeaderBy)
+			}
+		}
+		result = append(result, fmt.Sprintf("%s\x1f%s\x1f%s\x1f%s\x1f%v\x1f%s\x1f%v\x1f%s",
+			s.Node, s.ID, s.Address, state, s.Voter, raftProtocol, serverLastIndex, trailsLeaderByText))
 	}
 
 	return columnize.Format(result, &columnize.Config{Delim: string([]byte{0x1f})}), nil

command/operator/raft/listpeers/operator_raft_list_test.go

@@ -28,7 +28,7 @@ func TestOperatorRaftListPeersCommand(t *testing.T) {
 	a := agent.NewTestAgent(t, ``)
 	defer a.Shutdown()
 
-	expected := fmt.Sprintf("%s  %s  127.0.0.1:%d  leader  true   3",
+	expected := fmt.Sprintf("%s  %s  127.0.0.1:%d  leader  true   3             1             -",
 		a.Config.NodeName, a.Config.NodeID, a.Config.ServerPort)
 
 	// Test the list-peers subcommand directly

website/content/commands/operator/raft.mdx

@@ -70,7 +70,7 @@ configuration.
 
 - `-stale` - Enables non-leader servers to provide cluster state information.
   If the cluster is in an outage state without a leader,
-  we recommend setting this option to `true.
+  we recommend setting this option to `true`.
   Default is `false`.
 
 ## remove-peer