coder
diff --git a/‎enterprise/tailnet/coordinator.go
+60-14 b/‎enterprise/tailnet/coordinator.go
+60-14
@@ -13,6 +13,7 @@ import (
 	"time"
 
 	"github.com/google/uuid"
+	lru "github.com/hashicorp/golang-lru/v2"
 	"golang.org/x/xerrors"
 
 	"cdr.dev/slog"
@@ -24,15 +25,22 @@ import (
 // that uses PostgreSQL pubsub to exchange handshakes.
 func NewCoordinator(logger slog.Logger, pubsub database.Pubsub) (agpl.Coordinator, error) {
 	ctx, cancelFunc := context.WithCancel(context.Background())
+
+	nameCache, err := lru.New[uuid.UUID, string](512)
+	if err != nil {
+		panic("make lru cache: " + err.Error())
+	}
+
 	coord := &haCoordinator{
 		id:                       uuid.New(),
 		log:                      logger,
 		pubsub:                   pubsub,
 		closeFunc:                cancelFunc,
 		close:                    make(chan struct{}),
 		nodes:                    map[uuid.UUID]*agpl.Node{},
-		agentSockets:             map[uuid.UUID]net.Conn{},
-		agentToConnectionSockets: map[uuid.UUID]map[uuid.UUID]net.Conn{},
+		agentSockets:             map[uuid.UUID]*agpl.TrackedConn{},
+		agentToConnectionSockets: map[uuid.UUID]map[uuid.UUID]*agpl.TrackedConn{},
+		agentNameCache:           nameCache,
 	}
 
 	if err := coord.runPubsub(ctx); err != nil {
@@ -53,10 +61,14 @@ type haCoordinator struct {
 	// nodes maps agent and connection IDs their respective node.
 	nodes map[uuid.UUID]*agpl.Node
 	// agentSockets maps agent IDs to their open websocket.
-	agentSockets map[uuid.UUID]net.Conn
+	agentSockets map[uuid.UUID]*agpl.TrackedConn
 	// agentToConnectionSockets maps agent IDs to connection IDs of conns that
 	// are subscribed to updates for that agent.
-	agentToConnectionSockets map[uuid.UUID]map[uuid.UUID]net.Conn
+	agentToConnectionSockets map[uuid.UUID]map[uuid.UUID]*agpl.TrackedConn
+
+	// agentNameCache holds a cache of agent names. If one of them disappears,
+	// it's helpful to have a name cached for debugging.
+	agentNameCache *lru.Cache[uuid.UUID, string]
 }
 
 // Node returns an in-memory node by ID.
@@ -94,12 +106,18 @@ func (c *haCoordinator) ServeClient(conn net.Conn, id uuid.UUID, agent uuid.UUID
 	c.mutex.Lock()
 	connectionSockets, ok := c.agentToConnectionSockets[agent]
 	if !ok {
-		connectionSockets = map[uuid.UUID]net.Conn{}
+		connectionSockets = map[uuid.UUID]*agpl.TrackedConn{}
 		c.agentToConnectionSockets[agent] = connectionSockets
 	}
 
-	// Insert this connection into a map so the agent can publish node updates.
-	connectionSockets[id] = conn
+	now := time.Now().Unix()
+	// Insert this connection into a map so the agent
+	// can publish node updates.
+	connectionSockets[id] = &agpl.TrackedConn{
+		Conn:      conn,
+		Start:     now,
+		LastWrite: now,
+	}
 	c.mutex.Unlock()
 
 	defer func() {
@@ -176,7 +194,9 @@ func (c *haCoordinator) handleNextClientMessage(id, agent uuid.UUID, decoder *js
 
 // ServeAgent accepts a WebSocket connection to an agent that listens to
 // incoming connections and publishes node updates.
-func (c *haCoordinator) ServeAgent(conn net.Conn, id uuid.UUID, _ string) error {
+func (c *haCoordinator) ServeAgent(conn net.Conn, id uuid.UUID, name string) error {
+	c.agentNameCache.Add(id, name)
+
 	// Tell clients on other instances to send a callmemaybe to us.
 	err := c.publishAgentHello(id)
 	if err != nil {
@@ -196,21 +216,41 @@ func (c *haCoordinator) ServeAgent(conn net.Conn, id uuid.UUID, _ string) error
 		}
 	}
 
+	// This uniquely identifies a connection that belongs to this goroutine.
+	unique := uuid.New()
+	now := time.Now().Unix()
+	overwrites := int64(0)
+
 	// If an old agent socket is connected, we close it
 	// to avoid any leaks. This shouldn't ever occur because
 	// we expect one agent to be running.
 	c.mutex.Lock()
 	oldAgentSocket, ok := c.agentSockets[id]
 	if ok {
+		overwrites = oldAgentSocket.Overwrites + 1
 		_ = oldAgentSocket.Close()
 	}
-	c.agentSockets[id] = conn
+	c.agentSockets[id] = &agpl.TrackedConn{
+		ID:   unique,
+		Conn: conn,
+
+		Name:       name,
+		Start:      now,
+		LastWrite:  now,
+		Overwrites: overwrites,
+	}
 	c.mutex.Unlock()
+
 	defer func() {
 		c.mutex.Lock()
 		defer c.mutex.Unlock()
-		delete(c.agentSockets, id)
-		delete(c.nodes, id)
+
+		// Only delete the connection if it's ours. It could have been
+		// overwritten.
+		if idConn, ok := c.agentSockets[id]; ok && idConn.ID == unique {
+			delete(c.agentSockets, id)
+			delete(c.nodes, id)
+		}
 	}()
 
 	decoder := json.NewDecoder(conn)
@@ -576,8 +616,14 @@ func (c *haCoordinator) formatAgentUpdate(id uuid.UUID, node *agpl.Node) ([]byte
 	return buf.Bytes(), nil
 }
 
-func (*haCoordinator) ServeHTTPDebug(w http.ResponseWriter, _ *http.Request) {
+func (c *haCoordinator) ServeHTTPDebug(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
-	fmt.Fprintf(w, "<h1>coordinator</h1>")
-	fmt.Fprintf(w, "<h2>ha debug coming soon</h2>")
+
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+
+	fmt.Fprintln(w, "<h1>high-availability wireguard coordinator debug</h1>")
+	fmt.Fprintln(w, "<h4 style=\"margin-top:-25px\">warning: this only provides info from the node that served the request, if there are multiple replicas this data may be incomplete</h4>")
+
+	agpl.CoordinatorHTTPDebug(c.agentSockets, c.agentToConnectionSockets, c.agentNameCache)(w, r)
 }