diff --git a/lib/admin/__tests__/audit-log.test.ts b/lib/admin/__tests__/audit-log.test.ts
new file mode 100644
index 000000000..4cf7f8b24
--- /dev/null
+++ b/lib/admin/__tests__/audit-log.test.ts
@@ -0,0 +1,106 @@
+// @vitest-environment node
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { existsSync } from 'node:fs';
+import { mkdir, mkdtemp, readFile, rm, writeFile } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+
+// The admin audit log: today's audit.log in the state dir on one instance,
+// one log for every replica with a shared store (#1066).
+
+const log = vi.hoisted(() => ({ error: vi.fn(), warn: vi.fn(), info: vi.fn(), debug: vi.fn() }));
+vi.mock('@/lib/logger', () => ({ logger: log }));
+
+import { auditLog, readAuditLog } from '../audit';
+import { getStore, setStoreForTests } from '@/lib/shared-store';
+import { resetLocalStoreForTests } from '@/lib/shared-store/local';
+import { separateFakeStore } from './shared-store-fake';
+
+let dir: string;
+const statePath = (file: string) => path.join(dir, 'state', file);
+/** The shared log as another replica reads it. */
+const sharedLines = () => getStore().log('audit', {
+  local: { path: () => statePath('audit.log'), maxBytes: 10 * 1024 * 1024, rotations: 3 },
+  maxEntries: 50_000,
+}).readAll();
+
+beforeEach(async () => {
+  dir = await mkdtemp(path.join(tmpdir(), 'bw-audit-'));
+  vi.stubEnv('ADMIN_STATE_DIR', path.join(dir, 'state'));
+  resetLocalStoreForTests();
+  log.error.mockClear();
+});
+
+afterEach(async () => {
+  setStoreForTests(null);
+  resetLocalStoreForTests();
+  vi.unstubAllEnvs();
+  await rm(dir, { recursive: true, force: true });
+});
+
+describe('audit log on one instance', () => {
+  it('appends one JSON line per entry to audit.log and reads them newest first', async () => {
+    await auditLog('admin.login', {}, '203.0.113.1');
+    await auditLog('config.update', { changes: [{ key: 'sessionSecret', old: 'a', new: 'b' }] }, '203.0.113.2');
+    const lines = (await readFile(statePath('audit.log'), 'utf-8')).split('\n');
+    expect(lines).toHaveLength(3);
+    expect(lines[2]).toBe('');
+    expect(JSON.parse(lines[0])).toMatchObject({ action: 'admin.login', detail: {}, ip: '203.0.113.1' });
+    expect(Object.keys(JSON.parse(lines[0]))).toEqual(['ts', 'action', 'detail', 'ip']);
+    expect(JSON.parse(lines[1]).detail.changes[0]).toEqual({ key: 'sessionSecret', old: '[redacted]', new: '[redacted]' });
+
+    const { entries, total } = await readAuditLog();
+    expect(total).toBe(2);
+    expect(entries.map((e) => e.action)).toEqual(['config.update', 'admin.login']);
+  });
+
+  it('rotates audit.log at 10 MB and keeps three older files', async () => {
+    await mkdir(path.join(dir, 'state'), { recursive: true });
+    await writeFile(statePath('audit.log'), `${'x'.repeat(10 * 1024 * 1024)}\n`);
+    await writeFile(statePath('audit.log.1'), 'one\n');
+    await writeFile(statePath('audit.log.2'), 'two\n');
+    await writeFile(statePath('audit.log.3'), 'three\n');
+    await auditLog('admin.login', {}, '203.0.113.1');
+
+    expect(existsSync(statePath('audit.log'))).toBe(false);
+    expect((await readFile(statePath('audit.log.1'), 'utf-8')).endsWith('"ip":"203.0.113.1"}\n')).toBe(true);
+    expect(await readFile(statePath('audit.log.2'), 'utf-8')).toBe('one\n');
+    expect(await readFile(statePath('audit.log.3'), 'utf-8')).toBe('two\n');
+    expect(await readAuditLog()).toEqual({ entries: [], total: 0 });
+
+    await auditLog('admin.logout', {}, '203.0.113.1');
+    expect((await readAuditLog()).entries.map((e) => e.action)).toEqual(['admin.logout']);
+  });
+});
+
+describe('audit log with a shared store', () => {
+  let store: ReturnType<typeof separateFakeStore>;
+  beforeEach(() => {
+    store = separateFakeStore(path.join(dir, 'store'));
+    setStoreForTests(store);
+  });
+
+  it('keeps every entry of replicas writing at once, whole', async () => {
+    const replicas = await Promise.all([0, 1, 2].map(async () => {
+      vi.resetModules();
+      return (await import('../audit')).auditLog;
+    }));
+    await Promise.all(Array.from({ length: 60 }, (_, i) => replicas[i % 3]('admin.login', { n: i, note: 'line\nbreak' }, `198.51.100.${i}`)));
+
+    const lines = await sharedLines();
+    expect(lines).toHaveLength(60);
+    const numbers = lines.map((line) => JSON.parse(line).detail.n).sort((a, b) => a - b);
+    expect(numbers).toEqual(Array.from({ length: 60 }, (_, i) => i));
+    expect((await readAuditLog(1, 100)).total).toBe(60);
+    // Nothing in this replica's state dir.
+    expect(existsSync(statePath('audit.log'))).toBe(false);
+  });
+
+  it('puts the entry in the server log when the store is down', async () => {
+    store.down = true;
+    await expect(auditLog('admin.login_failed', {}, '203.0.113.9')).resolves.toBeUndefined();
+    expect(log.error).toHaveBeenCalledWith('Failed to write audit log', expect.objectContaining({
+      entry: expect.objectContaining({ action: 'admin.login_failed', ip: '203.0.113.9' }),
+    }));
+  });
+});
diff --git a/lib/admin/audit.ts b/lib/admin/audit.ts
index 8bc3b324e..0c4e2b6ed 100644
--- a/lib/admin/audit.ts
+++ b/lib/admin/audit.ts
@@ -1,6 +1,5 @@
-import { appendFile, stat, rename, readFile } from 'node:fs/promises';
-import { existsSync } from 'node:fs';
 import { logger } from '@/lib/logger';
+import { getStore, isSharedMode, type AppendLog, type LogOptions } from '@/lib/shared-store';
 import { ensureStateDir, getStatePath } from './paths';
 import { SENSITIVE_CONFIG_KEYS, type AuditEntry } from './types';
 
@@ -60,8 +59,19 @@ const MAX_LOG_SIZE = 10 * 1024 * 1024; // 10 MB
 const MAX_ROTATIONS = 3;
 const AUDIT_LOG_FILE = 'audit.log';
 
-function getAuditLogPath(): string {
-  return getStatePath(AUDIT_LOG_FILE);
+/**
+ * The audit log (#1066). Local mode: <state dir>/audit.log, rotated at
+ * 10 MB to .1 … .3, of which only the current file is read, as before.
+ * Shared mode: one log for every replica, keeping the newest 50 000
+ * entries (about what one 10 MB file holds).
+ */
+export const AUDIT_LOG_OPTIONS: LogOptions = {
+  local: { path: () => getStatePath(AUDIT_LOG_FILE), maxBytes: MAX_LOG_SIZE, rotations: MAX_ROTATIONS },
+  maxEntries: 50_000,
+};
+
+function auditStore(): AppendLog {
+  return getStore().log('audit', AUDIT_LOG_OPTIONS);
 }
 
 /**
@@ -69,7 +79,8 @@ function getAuditLogPath(): string {
  * so it remains writable when the config dir is mounted read-only.
  */
 export async function auditLog(action: string, detail: Record<string, unknown>, ip: string): Promise<void> {
-  await ensureStateDir();
+  const shared = isSharedMode();
+  if (!shared) await ensureStateDir();
 
   const entry: AuditEntry = {
     ts: new Date().toISOString(),
@@ -78,30 +89,16 @@ export async function auditLog(action: string, detail: Record<string, unknown>,
     ip,
   };
 
-  const logPath = getAuditLogPath();
   try {
-    await appendFile(logPath, JSON.stringify(entry) + '\n', 'utf-8');
-    await rotateIfNeeded(logPath);
+    // One line per entry; the store rotates the local file (audit.log.3 →
+    // deleted, .2 → .3, .1 → .2, audit.log → .1) once it passes 10 MB.
+    await auditStore().append(JSON.stringify(entry));
   } catch (error) {
-    logger.error('Failed to write audit log', { error: error instanceof Error ? error.message : 'Unknown error' });
-  }
-}
-
-async function rotateIfNeeded(logPath: string): Promise<void> {
-  try {
-    const stats = await stat(logPath);
-    if (stats.size < MAX_LOG_SIZE) return;
-
-    // Rotate: audit.log.3 → deleted, audit.log.2 → .3, audit.log.1 → .2, audit.log → .1
-    for (let i = MAX_ROTATIONS; i >= 1; i--) {
-      const from = i === 1 ? logPath : `${logPath}.${i - 1}`;
-      const to = `${logPath}.${i}`;
-      if (existsSync(from)) {
-        try { await rename(from, to); } catch { /* target may exist on overwrite */ }
-      }
-    }
-  } catch {
-    // stat failed, probably file doesn't exist yet
+    logger.error('Failed to write audit log', {
+      error: error instanceof Error ? error.message : 'Unknown error',
+      // With a shared store that is down, the entry is kept in the server log.
+      ...(shared ? { entry } : {}),
+    });
   }
 }
 
@@ -109,10 +106,8 @@ async function rotateIfNeeded(logPath: string): Promise<void> {
  * Read audit log entries, newest first. Supports pagination.
  */
 export async function readAuditLog(page: number = 1, limit: number = 50, actionFilter?: string): Promise<{ entries: AuditEntry[]; total: number }> {
-  const logPath = getAuditLogPath();
   try {
-    const content = await readFile(logPath, 'utf-8');
-    const lines = content.trim().split('\n').filter(Boolean);
+    const lines = await auditStore().readAll();
 
     let entries: AuditEntry[] = lines.map(line => {
       try { return JSON.parse(line); } catch { return null; }