diff --git a/packages/cluster/package.json b/packages/cluster/package.json
index 6899ec7b89..90d44b67fc 100644
--- a/packages/cluster/package.json
+++ b/packages/cluster/package.json
@@ -54,6 +54,7 @@
     "egg-logger": "catalog:",
     "get-ready": "catalog:",
     "graceful-process": "catalog:",
+    "onelogger": "^1.0.1",
     "sendmessage": "catalog:",
     "terminal-link": "catalog:",
     "utility": "catalog:"
diff --git a/packages/cluster/src/app_worker.ts b/packages/cluster/src/app_worker.ts
index 9d1cffdf09..185b455c96 100644
--- a/packages/cluster/src/app_worker.ts
+++ b/packages/cluster/src/app_worker.ts
@@ -8,6 +8,7 @@ import { debuglog } from 'node:util';
 import { importModule } from '@eggjs/utils';
 import { EggConsoleLogger as ConsoleLogger } from 'egg-logger';
 
+import { ipcLogger, formatIpcMessage, internalIpcLogEnabled } from './utils/ipc_logger.ts';
 import { BaseAppWorker } from './utils/mode/base/app.ts';
 import { AppProcessWorker } from './utils/mode/impl/process/app.ts';
 import { AppThreadWorker } from './utils/mode/impl/worker_threads/app.ts';
@@ -48,6 +49,25 @@ async function main() {
     AppWorker = AppThreadWorker as any;
   } else {
     AppWorker = AppProcessWorker as any;
+    // D. master -> app (recv): log every IPC message delivered to this worker via the cluster channel.
+    // Handle is present when master forwards a net.Socket (sticky-session mode).
+    // Read-only listener; other `process.on('message')` listeners (framework, sticky handler, etc.)
+    // are unaffected.
+    process.on('message', (msg: any, handle: any) => {
+      const body = typeof msg === 'string' ? { action: msg } : msg;
+      ipcLogger.info(formatIpcMessage(`app#${process.pid}<-master`, body, handle));
+    });
+
+    // F. master -> app internal NODE_CLUSTER messages (newconn with fd, disconnect, suicide, ...).
+    // `internalMessage` is an undocumented but stable Node.js event.
+    // Opt-in via EGG_CLUSTER_IPC_LOG because `newconn` fires once per HTTP request.
+    if (internalIpcLogEnabled) {
+      process.on('internalMessage', (msg: { cmd?: string; act?: string; ack?: number }, handle: unknown) => {
+        if (!msg || msg.cmd !== 'NODE_CLUSTER') return;
+        const label = msg.act ? `cluster:${msg.act}` : `cluster:ack#${msg.ack ?? '?'}`;
+        ipcLogger.info(formatIpcMessage(`app#${process.pid}<-master`, { action: label, data: msg }, handle));
+      });
+    }
   }
 
   const consoleLogger = new ConsoleLogger({
diff --git a/packages/cluster/src/master.ts b/packages/cluster/src/master.ts
index abcd45ff9b..c5bef8ac86 100644
--- a/packages/cluster/src/master.ts
+++ b/packages/cluster/src/master.ts
@@ -15,6 +15,7 @@ import terminalLink from 'terminal-link';
 import { readJSONSync } from 'utility';
 
 import { ClusterWorkerExceptionError } from './error/ClusterWorkerExceptionError.ts';
+import { ipcLogger, formatIpcMessage } from './utils/ipc_logger.ts';
 import { Messenger } from './utils/messenger.ts';
 import { AgentProcessWorker, AgentProcessUtils as ProcessAgentWorker } from './utils/mode/impl/process/agent.ts';
 import { AppProcessWorker, AppProcessUtils as ProcessAppWorker } from './utils/mode/impl/process/app.ts';
@@ -291,6 +292,11 @@ export class Master extends ReadyEventEmitter {
             connection.destroy();
           } else {
             const worker = this.stickyWorker(connection.remoteAddress) as AppProcessWorker;
+            // A'. master -> app sticky-session direct send (bypasses AppProcessWorker#send),
+            // carries a net.Socket handle — safe-printed by formatIpcMessage's replacer.
+            ipcLogger.info(
+              formatIpcMessage(`master->app#${worker.workerId}`, { action: 'sticky-session:connection' }, connection),
+            );
             worker.instance.send('sticky-session:connection', connection);
           }
         },
diff --git a/packages/cluster/src/utils/ipc_logger.ts b/packages/cluster/src/utils/ipc_logger.ts
new file mode 100644
index 0000000000..b8352dec9d
--- /dev/null
+++ b/packages/cluster/src/utils/ipc_logger.ts
@@ -0,0 +1,86 @@
+import net from 'node:net';
+
+import { getLogger } from 'onelogger';
+
+import type { MessageBody } from './messenger.ts';
+
+/**
+ * onelogger instance for Node.js cluster module IPC traffic between master and app workers.
+ * Users can override the underlying sink via `onelogger.setLogger()` / `setCustomLogger()`.
+ */
+export const ipcLogger = getLogger('egg/cluster/ipc');
+
+/**
+ * Whether internal-level cluster IPC logs (NODE_CLUSTER newconn/accepted/listening/...) are enabled.
+ * These are very verbose (one `cluster:newconn` per HTTP request), so they are opt-in
+ * via the `EGG_CLUSTER_IPC_LOG` environment variable (any truthy value enables).
+ */
+export const internalIpcLogEnabled = !!process.env.EGG_CLUSTER_IPC_LOG;
+
+const MAX_STRING_LEN = 200;
+const MAX_TOTAL_LEN = 1024;
+
+function describeHandle(handle: unknown): string {
+  if (handle == null) return '';
+  if (handle instanceof net.Socket) {
+    const fd = (handle as unknown as { _handle?: { fd?: number } })._handle?.fd;
+    return fd != null ? `<Socket fd=${fd}>` : '<Socket>';
+  }
+  if (handle instanceof net.Server) {
+    return '<Server>';
+  }
+  const ctor = (handle as { constructor?: { name?: string } })?.constructor?.name;
+  return ctor ? `<${ctor}>` : '<handle>';
+}
+
+function makeReplacer() {
+  const seen = new WeakSet<object>();
+  return function replacer(_key: string, value: unknown) {
+    if (value && typeof value === 'object') {
+      if (seen.has(value as object)) return '<Circular>';
+      seen.add(value as object);
+      if (value instanceof net.Socket) return describeHandle(value);
+      if (value instanceof net.Server) return '<Server>';
+      if (Buffer.isBuffer(value)) return `<Buffer len=${value.length}>`;
+    }
+    if (typeof value === 'string' && value.length > MAX_STRING_LEN) {
+      return `${value.slice(0, MAX_STRING_LEN)}...(truncated)`;
+    }
+    return value;
+  };
+}
+
+function stringifyData(data: unknown): string {
+  let out: string;
+  try {
+    out = JSON.stringify(data, makeReplacer());
+  } catch (err) {
+    return `<unserializable: ${(err as Error).message}>`;
+  }
+  if (out && out.length > MAX_TOTAL_LEN) {
+    out = `${out.slice(0, MAX_TOTAL_LEN)}...(truncated)`;
+  }
+  return out;
+}
+
+/**
+ * Format a single IPC message into a one-line log string.
+ * @param direction e.g. 'master->app#12345' / 'app#12345<-master'
+ * @param msg       the message body (supports cluster internal msgs via `action: 'cluster:<act>'`)
+ * @param handle    optional handle (net.Socket / net.Server / TCP) attached to the IPC message
+ */
+export function formatIpcMessage(
+  direction: string,
+  msg: Partial<MessageBody> & { action?: string; data?: unknown },
+  handle?: unknown,
+): string {
+  const action = msg?.action ?? '<unknown>';
+  let out = `[${direction}] action=${action}`;
+  if (msg && msg.data !== undefined) {
+    out += ` data=${stringifyData(msg.data)}`;
+  }
+  if (handle) {
+    out += ` +handle=${describeHandle(handle)}`;
+  }
+  return out;
+}
diff --git a/packages/cluster/src/utils/mode/impl/process/app.ts b/packages/cluster/src/utils/mode/impl/process/app.ts
index 0c9895a94c..d45a034d42 100644
--- a/packages/cluster/src/utils/mode/impl/process/app.ts
+++ b/packages/cluster/src/utils/mode/impl/process/app.ts
@@ -5,6 +5,7 @@ import { cfork } from 'cfork';
 import { graceful as gracefulExit, type Options as gracefulExitOptions } from 'graceful-process';
 import { sendmessage } from 'sendmessage';
 
+import { ipcLogger, formatIpcMessage, internalIpcLogEnabled } from '../../../ipc_logger.ts';
 import type { MessageBody } from '../../../messenger.ts';
 import { terminate } from '../../../terminate.ts';
 import { BaseAppWorker, BaseAppUtils } from '../../base/app.ts';
@@ -29,6 +30,7 @@ export class AppProcessWorker extends BaseAppWorker<ClusterProcessWorker> {
   }
 
   send(message: MessageBody): void {
+    ipcLogger.info(formatIpcMessage(`master->app#${this.workerId}`, message));
     sendmessage(this.instance, message);
   }
 
@@ -48,6 +50,7 @@ export class AppProcessWorker extends BaseAppWorker<ClusterProcessWorker> {
 
   static send(message: MessageBody): void {
     message.senderWorkerId = String(process.pid);
+    ipcLogger.info(formatIpcMessage(`app#${process.pid}->master`, message));
     // cluster won't get `listening` event when reusePort is true,
     // use cluster `message` event instead
     if (message.action === 'app-start' && message.reusePort) {
@@ -90,7 +93,10 @@ export class AppProcessUtils extends BaseAppUtils {
       const appWorker = new AppProcessWorker(worker);
       this.emit('worker_forked', appWorker);
       appWorker.disableRefork = true;
-      worker.on('message', (msg) => {
+      // B. master <- app (recv). Handle is present when master receives a net.Socket
+      // (e.g. forwarded sticky-session connection).
+      // Log AFTER forwarding to avoid adding log-serialization latency to the forward path.
+      worker.on('message', (msg, handle) => {
         if (typeof msg === 'string') {
           msg = {
             action: msg,
@@ -99,7 +105,21 @@ export class AppProcessUtils extends BaseAppUtils {
         }
         msg.from = 'app';
         this.messenger.send(msg);
+        ipcLogger.info(formatIpcMessage(`master<-app#${worker.process.pid}`, msg, handle));
       });
+
+      // E. cluster internal NODE_CLUSTER messages from worker to master:
+      // listening / online / queryServer / accepted (fd ack) / close / ...
+      // Must hook on `worker.process` (ChildProcess) — `cluster.Worker` doesn't forward `internalMessage`.
+      // `internalMessage` is undocumented but stable across Node.js versions.
+      // Opt-in via EGG_CLUSTER_IPC_LOG because this is verbose under load.
+      if (internalIpcLogEnabled) {
+        worker.process.on('internalMessage', (msg: { cmd?: string; act?: string; ack?: number }, handle: unknown) => {
+          if (!msg || msg.cmd !== 'NODE_CLUSTER') return;
+          const label = msg.act ? `cluster:${msg.act}` : `cluster:ack#${msg.ack ?? '?'}`;
+          ipcLogger.info(formatIpcMessage(`master<-app#${worker.process.pid}`, { action: label, data: msg }, handle));
+        });
+      }
       this.log(
         '[master] app_worker#%s:%s start, state: %s, current workers: %j',
         appWorker.id,