Optimize Idle CPU/Dash

app.js

@@ -107,11 +107,7 @@ function bindLivePeer(conn) {
   if (conn.capability) entry.capability = conn.capability;
   updateConnectionStatus(topicId, true);
   updateConnectionDisplay(topicId);
-  // Restart per-peer health UI loop (clears itself if peer drops)
+  // Sync health UI from live peer (manager health loop owns pings — no second interval)
-  if (entry.healthCheckInterval) {
-    clearInterval(entry.healthCheckInterval);
-    entry.healthCheckInterval = null;
-  }
   startHealthMonitoring(topicId);
 }
 
@@ -407,14 +403,22 @@ const volumesStore = {
 // Expose volumes store to window for use by other modules
 window.volumesStore = volumesStore;
 let lastStatsUpdate = Date.now();
+/**
+ * Legacy no-ops: live container stats arrive via push:allStats from the server.
+ * Kept as named exports so call sites stay stable without a 500ms wake timer.
+ */
 function stopStatsInterval() {
   if (statsInterval) {
     clearInterval(statsInterval);
     statsInterval = null;
-    console.log('[INFO] Stats interval stopped.');
   }
 }
 
+function startStatsInterval() {
+  // Clear any leftover timer from older sessions; do not schedule a new one.
+  stopStatsInterval();
+}
+
 // Utility functions are now imported from uiUtils.js
 
 
@@ -428,30 +432,6 @@ document.addEventListener('DOMContentLoaded', () => {
     });
   }
 });
-
-function startStatsInterval() {
-  // Guard: stop existing interval before starting a new one
-  stopStatsInterval();
-
-  // Only start if there's an active peer
-  if (!window.activePeer) {
-    console.warn('[WARN] No active peer; not starting stats interval.');
-    return;
-  }
-
-  // Increased interval to 500ms for better performance (was 100ms)
-  statsInterval = setInterval(() => {
-    if (window.activePeer) {
-      const now = Date.now();
-      if (now - lastStatsUpdate >= 500) { // Ensure at least 500ms between updates
-        lastStatsUpdate = now;
-      }
-    } else {
-      console.warn('[WARN] No active peer; skipping stats request.');
-      stopStatsInterval(); // Stop interval if peer is no longer active
-    }
-  }, 500); // Poll every 500ms for better performance (reduced from 100ms)
-}
 const smoothedStats = {}; // Container-specific smoothing storage
 const historicalStats = {}; // Container-specific historical stats for charts
 const MAX_HISTORY_POINTS = 900; // ~30m at 2s broadcast interval
@@ -2577,12 +2557,76 @@ document.addEventListener('DOMContentLoaded', () => {
 // Expose to window for onclick handlers
 window.navigateToView = navigateToView;
 
+/**
+ * Dashboard RPC TTL cache — avoids re-hitting the Docker socket on every
+ * navigation to the dashboard when nothing has changed.
+ * Invalidated on peer switch and on relevant list/event responses.
+ */
+const DASHBOARD_TTL = {
+  systemInfo: 30_000,
+  systemDf: 30_000,
+  containers: 10_000,
+  images: 20_000,
+  networks: 20_000,
+  volumes: 20_000,
+};
+
+/** @type {{ peerId: string, at: Record<string, number> }} */
+const dashboardRpcCache = { peerId: '', at: {} };
+
+function dashboardCachePeerId() {
+  return manager.active?.id || window.activePeer?.id || '';
+}
+
+function touchDashboardCache(key) {
+  const peerId = dashboardCachePeerId();
+  if (!peerId) return;
+  if (dashboardRpcCache.peerId !== peerId) {
+    dashboardRpcCache.peerId = peerId;
+    dashboardRpcCache.at = {};
+  }
+  dashboardRpcCache.at[key] = Date.now();
+}
+
+/**
+ * @param {string} key
+ * @param {number} [ttlMs]
+ */
+function isDashboardCacheFresh(key, ttlMs) {
+  const peerId = dashboardCachePeerId();
+  if (!peerId || dashboardRpcCache.peerId !== peerId) return false;
+  const at = dashboardRpcCache.at[key];
+  if (!at) return false;
+  const ttl = ttlMs ?? DASHBOARD_TTL[key] ?? 15_000;
+  return Date.now() - at < ttl;
+}
+
+/**
+ * @param {string|string[]|'all'} [keys]
+ */
+function invalidateDashboardCache(keys = 'all') {
+  if (keys === 'all') {
+    dashboardRpcCache.at = {};
+    return;
+  }
+  const list = Array.isArray(keys) ? keys : [keys];
+  for (const k of list) delete dashboardRpcCache.at[k];
+}
+
+window.invalidateDashboardCache = invalidateDashboardCache;
+
 // Dashboard Functions
 function loadDashboard() {
   if (!hasActiveConnection() && !window.activePeer) {
     return;
   }
 
+  const peerId = dashboardCachePeerId();
+  if (peerId && dashboardRpcCache.peerId !== peerId) {
+    dashboardRpcCache.peerId = peerId;
+    dashboardRpcCache.at = {};
+  }
+  
   // Set up volumes subscription early to catch broadcasts
   if (!volumesStoreSubscription) {
     volumesStoreSubscription = volumesStore.subscribe((volumes) => {
@@ -2628,22 +2672,27 @@ function loadDashboard() {
     })
     .catch(() => {});
 
-  // Load system info
+  // Only re-fetch slices that are stale — same data when fresh, less Docker socket load.
+  // When fresh, rely on event pushes + auto-refresh for updates.
+  if (!isDashboardCacheFresh('systemInfo')) {
     sendCommand('getSystemInfo');
+  }
+  if (!isDashboardCacheFresh('systemDf')) {
     sendCommand('getSystemDf');
-  
+  }
-  // Load container stats for counts
+  if (!isDashboardCacheFresh('containers')) {
     sendCommand('listContainers');
-  
+  }
-  // Load images count
+  if (!isDashboardCacheFresh('images')) {
     sendCommand('listImages');
-  
+  }
-  // Load networks count
+  if (!isDashboardCacheFresh('networks')) {
     sendCommand('listNetworks');
-  
+  }
-  // Load volumes
+  if (!isDashboardCacheFresh('volumes')) {
     sendCommand('listVolumes');
   }
+}
 
 window.loadDashboard = loadDashboard;
 
@@ -2662,6 +2711,7 @@ function formatBytes(bytes) {
 
 function refreshSystemDf() {
   if (!hasActiveConnection()) return;
+  invalidateDashboardCache('systemDf');
   sendCommand('getSystemDf');
 }
 window.refreshSystemDf = refreshSystemDf;
@@ -9773,6 +9823,7 @@ function handleRpcMessage(response, conn) {
             : null;
         if (rows) {
           applyContainerSnapshot(rows, topicId, { source: 'rpc' });
+          touchDashboardCache('containers');
           if (currentView === 'dashboard') {
             updateDashboardStats(containerFilterState.allContainers, null, null);
           }
@@ -9869,11 +9920,13 @@ function handleRpcMessage(response, conn) {
       case 'systemInfo':
         console.log('[INFO] Handling system information...');
         updateSystemInfo(response.data);
+        touchDashboardCache('systemInfo');
         break;
 
       case 'images':
         console.log('[INFO] Handling images list...');
         renderImages(response.data);
+        touchDashboardCache('images');
         // Update dashboard stats if on dashboard view
         if (currentView === 'dashboard') {
           updateDashboardStats(null, response.data, null);
@@ -9883,6 +9936,7 @@ function handleRpcMessage(response, conn) {
       case 'networks':
         console.log('[INFO] Handling networks list...');
         renderNetworks(response.data);
+        touchDashboardCache('networks');
         // Update dashboard stats if on dashboard view
         if (currentView === 'dashboard') {
           updateDashboardStats(null, null, response.data);
@@ -9903,6 +9957,7 @@ function handleRpcMessage(response, conn) {
         if (volumesToRender !== null) {
           // Always update store first (this will trigger subscriptions)
           volumesStore.set(volumesToRender);
+          touchDashboardCache('volumes');
           // Always render if on volumes view to ensure UI is updated
           if (currentView === 'volumes') {
             renderVolumes(volumesToRender);
@@ -9945,6 +10000,13 @@ function handleRpcMessage(response, conn) {
       }
 
       case 'dockerEvent': {
+        // Fleet-changing events: force dashboard slices to re-fetch on next visit
+        const ev = response.data || response;
+        const t = String(ev?.Type || ev?.type || '').toLowerCase();
+        if (t === 'container') invalidateDashboardCache('containers');
+        else if (t === 'image') invalidateDashboardCache(['images', 'systemDf']);
+        else if (t === 'volume') invalidateDashboardCache(['volumes', 'systemDf']);
+        else if (t === 'network') invalidateDashboardCache('networks');
         if (window.handleDockerEvent) {
           window.handleDockerEvent(response.data);
         }
@@ -10015,6 +10077,7 @@ function handleRpcMessage(response, conn) {
 
       case 'systemDf':
         renderSystemDf(response.data);
+        touchDashboardCache('systemDf');
         break;
 
       case 'containerTop':
@@ -11248,8 +11311,12 @@ function updateConnectionDisplay(topicId) {
     : String(fullKey);
 }
 
-// Health monitoring for connections (UI latency badge). Dead-link detection + reconnect
+/**
-// is owned by ConnectionManager's health loop / PearDockConnection.ping().
+ * Sync connection-row health UI from the live peer.
+ * Ping / dead-link detection is owned solely by ConnectionManager's health loop
+ * (manager emits 'health' → updateConnectionDisplay). A second interval here used
+ * to double docker.version() load on the server every 10s.
+ */
 function startHealthMonitoring(topicId) {
   const connection = connections[topicId];
   if (!connection) return;
@@ -11258,36 +11325,20 @@ function startHealthMonitoring(topicId) {
     connection.healthCheckInterval = null;
   }
 
-  const healthCheckInterval = setInterval(async () => {
+  const peer =
-    const entry = connections[topicId];
+    connection.peer?.connected
-    // Prefer manager's live socket if UI map is briefly stale after reconnect
+      ? connection.peer
-    const peer = entry?.peer?.connected
-      ? entry.peer
       : manager.connections.get(topicId)?.connected
         ? manager.connections.get(topicId)
         : null;
-    if (!peer) {
+  if (!peer) return;
-      clearInterval(healthCheckInterval);
+  if (connection.peer !== peer) connection.peer = peer;
-      if (entry) entry.healthCheckInterval = null;
+
-      return;
+  connection.latency = peer.latency ?? connection.latency;
-    }
+  connection.healthStatus = peer.healthStatus || connection.healthStatus || 'healthy';
-    if (entry && entry.peer !== peer) entry.peer = peer;
+  connection.lastHealthCheck = peer.lastHealthCheck || connection.lastHealthCheck || Date.now();
-    try {
-      const ms = await peer.ping();
-      entry.latency = ms;
-      entry.lastHealthCheck = Date.now();
-      entry.healthStatus = ms < 5000 ? 'healthy' : 'slow';
   updateConnectionStatus(topicId, true);
   updateConnectionDisplay(topicId);
-    } catch (err) {
-      entry.healthStatus = 'unhealthy';
-      updateConnectionStatus(topicId, false);
-      updateConnectionDisplay(topicId);
-      // Do not clear forever — manager will disconnect + redial; bindLivePeer restarts this loop
-    }
-  }, 10000);
-
-  connections[topicId].healthCheckInterval = healthCheckInterval;
 }
 
 // Switch between connections
@@ -11336,6 +11387,7 @@ function switchConnection(topicId, opts = {}) {
   // Drop previous host's containers immediately so the table never mixes peers
   resetContainerList();
   containerStore.topicId = manager.active?.id || topicId || '';
+  invalidateDashboardCache('all');
   console.log(`[INFO] Switched to connection: ${topicId}`);
   startStatsInterval();
   sendCommand(Methods.listContainers);

server/core/peer-registry.js

@@ -9,20 +9,54 @@ export class PeerRegistry {
   constructor() {
     /** @type {Map<string, import('../rpc/session.js').PeerSession>} */
     this.sessions = new Map()
+    /** @type {Set<(size: number, prevSize: number) => void>} */
+    this._listeners = new Set()
+  }
+
+  /**
+   * Subscribe to peer count changes (add / remove / clear).
+   * @param {(size: number, prevSize: number) => void} fn
+   * @returns {() => void} unsubscribe
+   */
+  onChange(fn) {
+    if (typeof fn !== 'function') return () => {}
+    this._listeners.add(fn)
+    return () => {
+      this._listeners.delete(fn)
+    }
+  }
+
+  /**
+   * @param {number} prevSize
+   */
+  _emitChange(prevSize) {
+    const size = this.sessions.size
+    if (size === prevSize) return
+    for (const fn of this._listeners) {
+      try {
+        fn(size, prevSize)
+      } catch (err) {
+        log.debug('onChange listener failed', { error: err?.message })
+      }
+    }
   }
 
   /**
    * @param {import('../rpc/session.js').PeerSession} session
    */
   add(session) {
+    const prev = this.sessions.size
     this.sessions.set(session.id, session)
+    this._emitChange(prev)
   }
 
   /**
    * @param {string} id
    */
   remove(id) {
-    this.sessions.delete(id)
+    const prev = this.sessions.size
+    const had = this.sessions.delete(id)
+    if (had) this._emitChange(prev)
   }
 
   /**
@@ -46,6 +80,7 @@ export class PeerRegistry {
    * @param {unknown} payload
    */
   broadcast(method, payload) {
+    if (this.sessions.size === 0) return
     for (const session of this.sessions.values()) {
       try {
         session.push(method, payload)
@@ -60,6 +95,7 @@ export class PeerRegistry {
   }
 
   clear() {
+    const prev = this.sessions.size
     for (const session of this.sessions.values()) {
       try {
         session.destroy()
@@ -68,6 +104,7 @@ export class PeerRegistry {
       }
     }
     this.sessions.clear()
+    this._emitChange(prev)
   }
 }
 

server/handlers/system.js

@@ -20,20 +20,89 @@ import logger from '../utils/logger.js'
 /** @type {Map<string, { username: string, serveraddress?: string }>} */
 const registryAuth = new Map()
 
-export function registerSystemHandlers(session) {
+/**
-  session.respond('ping', async () => {
+ * Cached Docker probe for high-frequency ping RPCs.
+ * Clients poll health every ~10s; version() is heavier than needed every tick.
+ * TTL keeps degraded detection responsive without hammering the socket.
+ */
+const PING_DOCKER_CACHE_TTL_MS = 10_000
+/** @type {{ at: number, ok: boolean, apiVersion: string|null, os: string|null, error: string|null }|null} */
+let pingDockerCache = null
+
+/**
+ * Lightweight Docker health for ping. Uses docker.ping() for liveness; refreshes
+ * apiVersion/os via version() only when cache is cold or after a failure.
+ * @returns {Promise<{ ok: boolean, apiVersion: string|null, os: string|null, error: string|null }>}
+ */
+export async function probeDockerForPing() {
+  const now = Date.now()
+  if (
+    pingDockerCache &&
+    now - pingDockerCache.at < PING_DOCKER_CACHE_TTL_MS &&
+    pingDockerCache.ok
+  ) {
+    return {
+      ok: true,
+      apiVersion: pingDockerCache.apiVersion,
+      os: pingDockerCache.os,
+      error: null,
+    }
+  }
+
   let dockerOk = false
-    let apiVersion = null
+  let apiVersion = pingDockerCache?.apiVersion ?? null
-    let osType = null
+  let osType = pingDockerCache?.os ?? null
   let error = null
+
   try {
+    // Prefer cheap ping; fall back to version if ping is unavailable
+    if (typeof docker.ping === 'function') {
+      await docker.ping()
+      dockerOk = true
+      // Refresh version metadata when cache empty or expired
+      if (!apiVersion || !pingDockerCache || now - pingDockerCache.at >= PING_DOCKER_CACHE_TTL_MS) {
+        try {
+          const version = await docker.version()
+          apiVersion = version.ApiVersion || version.apiVersion || apiVersion
+          osType = version.Os || version.os || osType
+        } catch {
+          // ok remains true from ping; version is optional decoration
+        }
+      }
+    } else {
       const version = await docker.version()
       dockerOk = true
       apiVersion = version.ApiVersion || version.apiVersion || null
       osType = version.Os || version.os || null
-    } catch (err) {
-      error = err.message
     }
+  } catch (err) {
+    error = err.message || String(err)
+    dockerOk = false
+  }
+
+  pingDockerCache = {
+    at: Date.now(),
+    ok: dockerOk,
+    apiVersion,
+    os: osType,
+    error,
+  }
+  return {
+    ok: dockerOk,
+    apiVersion,
+    os: osType,
+    error,
+  }
+}
+
+/** Test helper: clear ping Docker probe cache */
+export function clearPingDockerCache() {
+  pingDockerCache = null
+}
+
+export function registerSystemHandlers(session) {
+  session.respond('ping', async () => {
+    const dockerProbe = await probeDockerForPing()
     return {
       success: true,
       pong: Date.now(),
@@ -41,10 +110,10 @@ export function registerSystemHandlers(session) {
       protocolVersion: PROTOCOL_VERSION,
       role: session.role,
       docker: {
-        ok: dockerOk,
+        ok: dockerProbe.ok,
-        apiVersion,
+        apiVersion: dockerProbe.apiVersion,
-        os: osType,
+        os: dockerProbe.os,
-        error,
+        error: dockerProbe.error,
       },
       features: {
         swarm: isSwarmEnabled(),

server/services/alerts.js

@@ -1073,10 +1073,18 @@ async function pollHealth() {
     return // skip further polls if docker is down
   }
 
+  // One listContainers for both container_health and stack_health (half the socket work)
+  /** @type {object[]} */
+  let containers = []
+  try {
+    containers = (await docker.listContainers({ all: true })) || []
+  } catch (err) {
+    logger.debug('alerts: container list poll failed', { error: err.message })
+  }
+
   // Container health
   try {
-    const containers = await docker.listContainers({ all: true })
+    for (const c of containers) {
-    for (const c of containers || []) {
       const health = c.Status?.match(/\((healthy|unhealthy|health: starting)\)/i)?.[1]
         || c.State // running/exited — Health may be in inspect only
       // Prefer Health from inspect-lite if present
@@ -1098,10 +1106,9 @@ async function pollHealth() {
 
   // Stack / compose project health (group by com.docker.compose.project)
   try {
-    const containers = await docker.listContainers({ all: true })
     /** @type {Map<string, { name: string, running: number, total: number, unhealthy: number }>} */
     const stacks = new Map()
-    for (const c of containers || []) {
+    for (const c of containers) {
       const project =
         c.Labels?.['com.docker.compose.project'] ||
         c.Labels?.['com.docker.stack.namespace']

server/services/events.js

@@ -39,9 +39,11 @@ const CONTAINER_LIST_ACTIONS = new Set([
 ])
 
 function scheduleContainerListBroadcast() {
+  if (peers.size === 0) return
   if (containerListBroadcastTimer) return
   containerListBroadcastTimer = setTimeout(() => {
     containerListBroadcastTimer = null
+    if (peers.size === 0) return
     broadcastContainers().catch((err) => {
       logger.debug('container list broadcast failed', { error: err.message })
     })
@@ -49,9 +51,11 @@ function scheduleContainerListBroadcast() {
 }
 
 function scheduleImageListBroadcast() {
+  if (peers.size === 0) return
   if (imageListBroadcastTimer) return
   imageListBroadcastTimer = setTimeout(() => {
     imageListBroadcastTimer = null
+    if (peers.size === 0) return
     broadcastImages().catch((err) => {
       logger.debug('image list broadcast failed', { error: err.message })
     })
@@ -95,18 +99,13 @@ async function openEventStream() {
           }
           if (event.status === 'undefined') continue
 
-          logger.info('Docker event', {
+          logger.debug('Docker event', {
             status: event.status,
             id: event.id,
             type: event.Type,
             action: event.Action,
           })
 
-          peers.broadcast(Pushes.dockerEvent, {
-            type: 'dockerEvent',
-            data: event,
-          })
-
           // Server-side alerting (webhooks) — independent of connected clients
           try {
             onDockerEvent(event)
@@ -114,6 +113,14 @@ async function openEventStream() {
             logger.debug('alerts onDockerEvent error', { error: e?.message })
           }
 
+          // Skip client fan-out when idle (no peers) — alerts already handled above
+          if (peers.size > 0) {
+            peers.broadcast(Pushes.dockerEvent, {
+              type: 'dockerEvent',
+              data: event,
+            })
+          }
+
           // Do not rebroadcast the full list on every exec_*/health_status event —
           // that thrashed clients (rows flicker / disappear on each refresh).
           if (event.Type === 'container') {
@@ -127,7 +134,11 @@ async function openEventStream() {
             scheduleImageListBroadcast()
           }
 
-          if (event.Type === 'volume' && (event.Action === 'create' || event.Action === 'destroy')) {
+          if (
+            peers.size > 0 &&
+            event.Type === 'volume' &&
+            (event.Action === 'create' || event.Action === 'destroy')
+          ) {
             const volumesResult = await docker.listVolumes()
             const volumesList = extractVolumesList(volumesResult)
             peers.broadcast(Pushes.volumes, {

server/services/stats.js

@@ -9,10 +9,14 @@ import { docker, extractIpAddress } from './docker.js'
 import { peers } from '../core/peer-registry.js'
 import { Pushes } from '../../shared/protocol.js'
 import { recordSample, pruneMissing } from './stats-history.js'
+import { CONFIG } from '../../config.js'
 import logger from '../utils/logger.js'
 
-const STATS_CACHE_TTL = 1000
+const STATS_CACHE_TTL = CONFIG.STATS?.CACHE_TTL_MS ?? 1000
-const STATS_BROADCAST_INTERVAL = 2000
+/** How often we tick collection when peers are connected */
+const STATS_COLLECT_INTERVAL = CONFIG.STATS?.ACTIVE_INTERVAL_MS ?? 1000
+/** Minimum gap between allStats broadcasts */
+const STATS_BROADCAST_INTERVAL = CONFIG.STATS?.INTERVAL_MS ?? 2000
 
 /** @type {Record<string, object>} */
 const containerStats = {}
@@ -20,6 +24,15 @@ const statsCache = new Map()
 const containerActivity = new Map()
 
 let intervalHandle = null
+/** Peer-registry unsubscribe; set while stats service is armed */
+let unsubPeers = null
+/** True after startStatsBroadcast(); false after stopStatsBroadcast() */
+let serviceArmed = false
+let lastBroadcast = 0
+let dockerDownLogged = false
+let dockerBackoffUntil = 0
+/** Serialize ticks so overlapping async collects cannot pile up */
+let tickInFlight = false
 
 /**
  * Docker Engine CPU % (same idea as `docker stats`).
@@ -332,13 +345,39 @@ async function collectContainerStats() {
   }
 }
 
-export function startStatsBroadcast() {
+/**
-  if (intervalHandle) return
+ * Tear down all live stats streams and in-memory collection state.
-  let lastBroadcast = 0
+ * Used when the last peer disconnects so Docker is not polled idle.
-  let dockerDownLogged = false
+ */
-  let dockerBackoffUntil = 0
+function destroyAllStatsEntries() {
+  for (const id of Object.keys(containerStats)) {
+    destroyStatsEntry(id)
+  }
+  statsCache.clear()
+  containerActivity.clear()
+}
 
-  intervalHandle = setInterval(async () => {
+/**
+ * Pause collection: stop interval and drop Docker stats streams.
+ * Safe to call when already paused.
+ */
+export function pauseStatsCollection() {
+  if (intervalHandle) {
+    clearInterval(intervalHandle)
+    intervalHandle = null
+  }
+  destroyAllStatsEntries()
+  tickInFlight = false
+  logger.debug('Stats collection paused (no peers)')
+}
+
+async function statsTick() {
+  if (tickInFlight) return
+  if (peers.size === 0) {
+    pauseStatsCollection()
+    return
+  }
+  tickInFlight = true
   try {
     const now = Date.now()
     if (now < dockerBackoffUntil) return
@@ -346,8 +385,13 @@ export function startStatsBroadcast() {
     await collectContainerStats()
     dockerDownLogged = false
 
+    // Peer may have left while we were collecting
+    if (peers.size === 0) {
+      pauseStatsCollection()
+      return
+    }
+
     if (now - lastBroadcast < STATS_BROADCAST_INTERVAL) return
-      if (peers.size === 0) return
 
     const aggregatedStats = []
     for (const [containerId, statsData] of Object.entries(containerStats)) {
@@ -420,16 +464,80 @@ export function startStatsBroadcast() {
     } else {
       logger.error('Stats broadcast failed', { error: msg })
     }
+  } finally {
+    tickInFlight = false
   }
-  }, 1000)
 }
 
+/**
+ * Resume collection when at least one peer is connected.
+ * Idempotent; kicks an immediate tick so first client is not waiting a full interval.
+ */
+export function resumeStatsCollection() {
+  if (!serviceArmed) return
+  if (peers.size === 0) return
+  if (!intervalHandle) {
+    intervalHandle = setInterval(() => {
+      statsTick().catch(() => {})
+    }, STATS_COLLECT_INTERVAL)
+    if (typeof intervalHandle.unref === 'function') intervalHandle.unref()
+    logger.debug('Stats collection resumed', { peers: peers.size })
+  }
+  // Immediate kick so first connected client gets streams ASAP
+  lastBroadcast = 0
+  statsTick().catch(() => {})
+}
+
+function onPeerCountChange(size, prevSize) {
+  if (!serviceArmed) return
+  if (size > 0 && prevSize === 0) {
+    resumeStatsCollection()
+  } else if (size === 0 && prevSize > 0) {
+    pauseStatsCollection()
+  }
+}
+
+/**
+ * Arm the stats service. Collection only runs while peers.size > 0.
+ * Call once at server boot (safe if already started).
+ */
+export function startStatsBroadcast() {
+  if (serviceArmed) return
+  serviceArmed = true
+  lastBroadcast = 0
+  dockerDownLogged = false
+  dockerBackoffUntil = 0
+
+  if (!unsubPeers) {
+    unsubPeers = peers.onChange(onPeerCountChange)
+  }
+
+  if (peers.size > 0) {
+    resumeStatsCollection()
+  } else {
+    // Explicit idle: no interval, no Docker stats streams
+    pauseStatsCollection()
+    logger.debug('Stats service armed (idle until first peer)')
+  }
+}
+
+/**
+ * Fully stop the stats service (process shutdown).
+ */
 export function stopStatsBroadcast() {
-  if (intervalHandle) {
+  serviceArmed = false
-    clearInterval(intervalHandle)
+  if (unsubPeers) {
-    intervalHandle = null
+    try {
+      unsubPeers()
+    } catch {
+      // ignore
     }
-  for (const id of Object.keys(containerStats)) {
+    unsubPeers = null
-    destroyStatsEntry(id)
   }
+  pauseStatsCollection()
+}
+
+/** @returns {boolean} whether the collect interval is currently running */
+export function isStatsCollectionActive() {
+  return Boolean(intervalHandle)
 }

test/ping-cache.test.js

@@ -0,0 +1,74 @@
+/**
+ * ping RPC Docker probe cache — second call within TTL must not re-hit Docker.
+ */
+import test from 'brittle'
+
+test('probeDockerForPing caches successful probes within TTL', async (t) => {
+  // Mock dockerode-style client on the module under test via dynamic import is hard;
+  // exercise the exported helpers by stubbing the docker export.
+  const dockerMod = await import('../server/services/docker.js')
+  const system = await import('../server/handlers/system.js')
+
+  system.clearPingDockerCache()
+
+  let pingCalls = 0
+  let versionCalls = 0
+  const origPing = dockerMod.docker.ping
+  const origVersion = dockerMod.docker.version
+
+  dockerMod.docker.ping = async () => {
+    pingCalls += 1
+    return {}
+  }
+  dockerMod.docker.version = async () => {
+    versionCalls += 1
+    return { ApiVersion: '1.45', Os: 'linux' }
+  }
+
+  try {
+    const a = await system.probeDockerForPing()
+    t.ok(a.ok)
+    t.is(a.apiVersion, '1.45')
+    t.is(pingCalls, 1)
+    t.ok(versionCalls >= 1)
+
+    const pingsBefore = pingCalls
+    const versionsBefore = versionCalls
+    const b = await system.probeDockerForPing()
+    t.ok(b.ok)
+    t.is(b.apiVersion, '1.45')
+    t.is(pingCalls, pingsBefore, 'cached: no second docker.ping')
+    t.is(versionCalls, versionsBefore, 'cached: no second docker.version')
+  } finally {
+    dockerMod.docker.ping = origPing
+    dockerMod.docker.version = origVersion
+    system.clearPingDockerCache()
+  }
+})
+
+test('probeDockerForPing re-probes after failed cache / clear', async (t) => {
+  const dockerMod = await import('../server/services/docker.js')
+  const system = await import('../server/handlers/system.js')
+  system.clearPingDockerCache()
+
+  let pingCalls = 0
+  const origPing = dockerMod.docker.ping
+  const origVersion = dockerMod.docker.version
+  dockerMod.docker.ping = async () => {
+    pingCalls += 1
+    return {}
+  }
+  dockerMod.docker.version = async () => ({ ApiVersion: '1.44', Os: 'linux' })
+
+  try {
+    await system.probeDockerForPing()
+    t.is(pingCalls, 1)
+    system.clearPingDockerCache()
+    await system.probeDockerForPing()
+    t.is(pingCalls, 2, 'after clear, probes again')
+  } finally {
+    dockerMod.docker.ping = origPing
+    dockerMod.docker.version = origVersion
+    system.clearPingDockerCache()
+  }
+})

test/stats-idle.test.js

@@ -0,0 +1,90 @@
+/**
+ * Peer-demand stats: no Docker collection while zero peers.
+ */
+import test from 'brittle'
+import { PeerRegistry } from '../server/core/peer-registry.js'
+
+test('PeerRegistry onChange fires on add/remove and size transitions', (t) => {
+  const reg = new PeerRegistry()
+  /** @type {Array<[number, number]>} */
+  const events = []
+  const unsub = reg.onChange((size, prev) => events.push([size, prev]))
+
+  const s1 = { id: 'peer-aaa', destroy() {} }
+  const s2 = { id: 'peer-bbb', destroy() {} }
+
+  reg.add(s1)
+  t.is(reg.size, 1)
+  t.alike(events[events.length - 1], [1, 0])
+
+  reg.add(s2)
+  t.is(reg.size, 2)
+  t.alike(events[events.length - 1], [2, 1])
+
+  reg.remove('peer-aaa')
+  t.is(reg.size, 1)
+  t.alike(events[events.length - 1], [1, 2])
+
+  reg.remove('peer-bbb')
+  t.is(reg.size, 0)
+  t.alike(events[events.length - 1], [0, 1])
+
+  // remove missing id is no-op (no event)
+  const n = events.length
+  reg.remove('nope')
+  t.is(events.length, n)
+
+  unsub()
+  reg.add(s1)
+  t.is(events.length, n, 'unsubscribed listener not called')
+  reg.clear()
+})
+
+test('PeerRegistry.broadcast is a no-op with zero peers', (t) => {
+  const reg = new PeerRegistry()
+  let pushed = 0
+  reg.broadcast('push:test', { x: 1 })
+  t.is(pushed, 0)
+
+  reg.add({
+    id: 'p1',
+    push() {
+      pushed += 1
+    },
+    destroy() {},
+  })
+  reg.broadcast('push:test', { x: 1 })
+  t.is(pushed, 1)
+  reg.clear()
+})
+
+test('stats service: idle when no peers; active when peer present', async (t) => {
+  // Isolate module state by dynamic import after resetting — use public API only.
+  const stats = await import('../server/services/stats.js')
+  const { peers } = await import('../server/core/peer-registry.js')
+
+  // Ensure clean slate from any prior test importing peers
+  peers.clear()
+  stats.stopStatsBroadcast()
+
+  stats.startStatsBroadcast()
+  t.is(stats.isStatsCollectionActive(), false, 'no collect interval with 0 peers')
+
+  const fake = {
+    id: 'test-peer-stats-idle',
+    role: 'viewer',
+    push() {},
+    destroy() {},
+  }
+  peers.add(fake)
+  // resume is async-kicked; give microtask + timer a tick
+  await new Promise((r) => setTimeout(r, 50))
+  t.is(stats.isStatsCollectionActive(), true, 'collect interval after first peer')
+
+  peers.remove(fake.id)
+  await new Promise((r) => setTimeout(r, 20))
+  t.is(stats.isStatsCollectionActive(), false, 'collect interval stopped after last peer')
+
+  stats.stopStatsBroadcast()
+  peers.clear()
+})

ui/ops-app.js

@@ -586,6 +586,10 @@ export function saveSettings(partial) {
 
 /** @type {ReturnType<typeof setInterval>|null} */
 let listRefreshTimer = null
+/** Seconds last applied to auto-refresh (for visibility resume) */
+let listRefreshSeconds = 0
+/** Whether visibility listener is attached */
+let listRefreshVisibilityWired = false
 
 export function applySettings(s = loadSettings()) {
   document.body.dataset.density = s.density || 'comfortable'
@@ -674,17 +678,11 @@ export function shouldShowFirstConnectTip() {
 }
 
 /**
- * Poll the active resource list when Settings auto-refresh > 0.
+ * One auto-refresh tick for the active view (shared by interval + visibility resume).
- * @param {number} [seconds]
  */
-export function startListAutoRefresh(seconds) {
+function runListAutoRefreshTick() {
-  if (listRefreshTimer) {
+  // Do not hammer Docker while the window/tab is backgrounded
-    clearInterval(listRefreshTimer)
+  if (typeof document !== 'undefined' && document.hidden) return
-    listRefreshTimer = null
-  }
-  const sec = Number(seconds ?? loadSettings().refreshSeconds ?? 0)
-  if (!sec || sec < 1) return
-  listRefreshTimer = setInterval(() => {
   if (!manager.active?.connected) return
   const view = typeof window !== 'undefined' ? window.currentView : null
   const send = typeof window !== 'undefined' ? window.sendCommand : null
@@ -705,6 +703,36 @@ export function startListAutoRefresh(seconds) {
   } catch {
     // ignore
   }
+}
+
+function wireListRefreshVisibility() {
+  if (listRefreshVisibilityWired || typeof document === 'undefined') return
+  listRefreshVisibilityWired = true
+  document.addEventListener('visibilitychange', () => {
+    if (document.hidden) return
+    // On focus: one catch-up tick if auto-refresh is enabled
+    if (listRefreshSeconds >= 1 && manager.active?.connected) {
+      runListAutoRefreshTick()
+    }
+  })
+}
+
+/**
+ * Poll the active resource list when Settings auto-refresh > 0.
+ * Skips ticks while document.hidden to avoid idle Docker socket load.
+ * @param {number} [seconds]
+ */
+export function startListAutoRefresh(seconds) {
+  if (listRefreshTimer) {
+    clearInterval(listRefreshTimer)
+    listRefreshTimer = null
+  }
+  const sec = Number(seconds ?? loadSettings().refreshSeconds ?? 0)
+  listRefreshSeconds = sec > 0 ? sec : 0
+  if (!sec || sec < 1) return
+  wireListRefreshVisibility()
+  listRefreshTimer = setInterval(() => {
+    runListAutoRefreshTick()
   }, sec * 1000)
 }