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CDN / 静态资源故障容灾

场景​

CDN 服务故障或某个静态资源加载失败，导致页面白屏或功能异常。如何设计容灾方案？

分析思路​

资源加载失败的检测​

全局资源错误监听
window.addEventListener('error', (e) => {
  const target = e.target as HTMLElement;
  if (target?.tagName) {
    const src = (target as HTMLScriptElement).src
      || (target as HTMLLinkElement).href
      || (target as HTMLImageElement).src;

    console.error(`资源加载失败: ${target.tagName} ${src}`);
    handleResourceError(target.tagName, src);
  }
}, true); // 捕获阶段

容灾方案​

方案 1：多 CDN 备份切换​

script 加载失败自动切换 CDN
const CDN_LIST = [
  'https://cdn1.example.com',
  'https://cdn2.example.com',
  'https://cdn3.example.com',
];

function loadScriptWithFallback(path: string, cdnIndex = 0): Promise<void> {
  if (cdnIndex >= CDN_LIST.length) {
    return Promise.reject(new Error(`所有 CDN 均不可用: ${path}`));
  }

  return new Promise((resolve, reject) => {
    const script = document.createElement('script');
    script.src = `${CDN_LIST[cdnIndex]}${path}`;
    script.onload = () => resolve();
    script.onerror = () => {
      console.warn(`CDN ${cdnIndex} 失败，尝试 CDN ${cdnIndex + 1}`);
      loadScriptWithFallback(path, cdnIndex + 1).then(resolve, reject);
    };
    document.head.appendChild(script);
  });
}

方案 2：Service Worker 缓存兜底​

sw.ts — 缓存关键资源
const CACHE_NAME = 'app-v1';
const CRITICAL_ASSETS = ['/index.html', '/main.js', '/style.css'];

self.addEventListener('install', (event: ExtendableEvent) => {
  event.waitUntil(
    caches.open(CACHE_NAME).then((cache) => cache.addAll(CRITICAL_ASSETS))
  );
});

self.addEventListener('fetch', (event: FetchEvent) => {
  event.respondWith(
    fetch(event.request).catch(() => {
      // 网络失败时从缓存读取
      return caches.match(event.request).then((cached) => {
        return cached || new Response('资源不可用', { status: 503 });
      });
    })
  );
});

方案 3：HTML 内联关键资源​

关键 CSS 内联到 HTML
<head>
  <!-- 关键 CSS 内联，不依赖外部资源 -->
  <style>
    body { margin: 0; font-family: system-ui; }
    .loading { display: flex; justify-content: center; align-items: center; height: 100vh; }
  </style>
</head>

常见面试问题​

Q1: CDN 挂了怎么办？​

答案：

  • 检测：window.addEventListener('error') 捕获资源加载失败
  • 自动切换：多 CDN 备份，失败时自动切换域名
  • 缓存兜底：Service Worker 缓存关键资源
  • 降级方案：CDN 全挂时展示本地缓存或静态兜底页面
  • 监控告警：CDN 资源加载失败率超阈值自动告警

相关链接​