{
  "topic": "cdn",
  "type": "single_choice",
  "schema_version": "1.0.0",
  "generated": "2026-09-02T21:20:00+08:00",
  "questions": [
    {
      "id": "sc-001",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "CDN",
        "边缘节点"
      ],
      "question": "CDN 的核心思想是什么？",
      "options": {
        "A": "所有用户直接访问源站",
        "B": "把资源复制到全球一堆服务器上，用户就近获取",
        "C": "使用加密传输",
        "D": "增加源站带宽"
      },
      "answer": "B",
      "explanation": "CDN 的核心思想是把资源复制到全世界的边缘节点上，用户就近访问最近的边缘节点，减少延迟和源站压力。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-002",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "CDN",
        "智能DNS"
      ],
      "question": "CDN 的智能 DNS 根据什么决定返回哪个边缘节点的 IP？",
      "options": {
        "A": "用户浏览器版本",
        "B": "请求来源 IP 的地理位置",
        "C": "服务器负载",
        "D": "随机选择"
      },
      "answer": "B",
      "explanation": "CDN 的 DNS 服务器根据请求来源 IP 的地理位置（通过 IP 地理位置数据库）来决定返回哪个边缘节点的 IP，这个过程对用户完全透明。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-003",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "CDN",
        "回源"
      ],
      "question": "CDN 的回源是什么意思？",
      "options": {
        "A": "用户直接访问源站",
        "B": "边缘节点缓存未命中时，去源站拉取文件",
        "C": "源站主动推送文件",
        "D": "DNS 解析失败"
      },
      "answer": "B",
      "explanation": "回源是指边缘节点缓存未命中时，去源站拉取文件。第一次请求会慢一点（回源），之后就快了（缓存命中）。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-004",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "CDN",
        "适合内容"
      ],
      "question": "以下哪种内容最适合上 CDN？",
      "options": {
        "A": "用户个人数据",
        "B": "实时交易数据",
        "C": "图片、JS、CSS 等静态资源",
        "D": "登录接口"
      },
      "answer": "C",
      "explanation": "CDN 适合缓存内容不怎么变、所有人看到的一样、可以缓存的静态资源。用户个人数据、实时交易数据、登录接口等需要实时性的内容不适合。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-005",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "CDN",
        "HTTPS终止"
      ],
      "question": "CDN 的 HTTPS 终止是什么意思？",
      "options": {
        "A": "禁止 HTTPS 访问",
        "B": "边缘节点处理 TLS 握手，到源站可以用 HTTP",
        "C": "源站不支持 HTTPS",
        "D": "CDN 自动升级到 HTTP/3"
      },
      "answer": "B",
      "explanation": "HTTPS 终止是指边缘节点处理 TLS 握手，到源站可以用 HTTP（内网更快）。用户←HTTPS→CDN 边缘节点←HTTP→源站。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-006",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "CDN",
        "DDoS"
      ],
      "question": "CDN 如何防 DDoS？",
      "options": {
        "A": "直接丢弃流量",
        "B": "攻击流量被分散到全球几百个边缘节点吸收",
        "C": "使用防火墙",
        "D": "关闭源站"
      },
      "answer": "B",
      "explanation": "CDN 防 DDoS 的原理是攻击流量被分散到全球几百个边缘节点吸收，源站几乎无感。这是 CDN 的核心能力之一。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-007",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "CDN",
        "缓存策略"
      ],
      "question": "Cache-Control: max-age=31536000, immutable 表示什么？",
      "options": {
        "A": "缓存 1 天",
        "B": "缓存 1 年，且不需要向源站发起条件请求",
        "C": "不缓存",
        "D": "缓存 5 分钟"
      },
      "answer": "B",
      "explanation": "max-age=31536000 表示缓存 1 年，immutable 告诉浏览器这个资源永远不会改变，不需要向源站发起条件请求（If-Modified-Since/ETag 验证）。适用于文件名带版本号的静态资源。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-008",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "CDN",
        "缓存分层"
      ],
      "question": "CDN 的缓存分层顺序正确的是？",
      "options": {
        "A": "源站 → 区域节点 → 边缘节点 → 用户",
        "B": "用户 → 边缘节点 → 区域节点 → 源站",
        "C": "用户 → 源站 → 边缘节点",
        "D": "边缘节点 → 用户 → 源站"
      },
      "answer": "B",
      "explanation": "CDN 缓存分层：用户 → 边缘节点（缓存1）→ 区域节点（缓存2）→ 源站（原始文件）。请求从用户开始，逐层向上查找缓存。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-009",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "CDN",
        "缓存一致性"
      ],
      "question": "更新了 logo.png 但 CDN 还缓存旧的，应该怎么解决？",
      "options": {
        "A": "等自然过期",
        "B": "文件名带版本号、调用 CDN API 强制清除缓存、或设置较短的 max-age",
        "C": "重启 CDN 服务器",
        "D": "删除源站文件"
      },
      "answer": "B",
      "explanation": "缓存一致性问题的解决方案：（1）文件名带版本号 /logo.v2.png；（2）调用 CDN API 强制清除缓存；（3）设置较短的 max-age 等自然过期。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-010",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "CDN",
        "源站压力"
      ],
      "question": "100 万用户访问 CDN，源站大约处理多少次请求？",
      "options": {
        "A": "100 万次",
        "B": "50 万次",
        "C": "1 万次",
        "D": "0 次"
      },
      "answer": "C",
      "explanation": "CDN 可以消化 99% 的流量，100 万用户 → 99 万次命中边缘节点 → 源站只处理约 1 万次回源。这是 CDN 减轻源站压力的核心能力。",
      "source": null,
      "related": []
    }
  ]
}