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DNS 基本概念 \n\nDNS（Domain Name System，域名系统）是因特网上用于将主机名转换为 IP 地址的协议。它是一个分布式数据库系统，通过将主机名映射到 IP 地址来实现主机名解析，并使用户能够通过更容易识别的主机名来访问互联网上的资源。\n\n在使用 DNS 协议进行主机名解析时，系统首先查询本地 DNS 缓存。如果缓存中不存在结果，系统将向本地 DNS 服务器发出请求，并逐级向上查找，直到找到权威 DNS 服务器并获得解析结果。在域名解析的过程中，DNS 协议采用了分级命名空间的结构，不同的域名可以通过点分隔符分为多个级别，例如 `www.example.com` 可以分为三个级别：`www`、`example` 和 `com`。\n\n除了将域名映射到 IP 地址之外，DNS 协议还支持多种其他功能：\n\n1. 逆向映射：将 IP 地址解析为域名。\n2. 邮件服务器设置：支持邮件服务器的自动发现和设置。\n3. 负载均衡：DNS 还可以实现简单的负载均衡，通过将相同 IP 地址的主机名映射到不同的 IP 地址来分散负载。\n4. 安全：DNSSEC（DNS Security Extensions，DNS 安全扩展）可以提供对域名解析的认证和完整性。\n\n### 如何加快 DNS 的解析？\n\n有以下几种方法可以加快 DNS 的解析：\n\n1. 使用高速 DNS 服务器：默认情况下，网络服务提供商（ISP）为其用户提供 DNS 服务器。但是，这些服务器不一定是最快的，有时会出现瓶颈。如果您想加快 DNS 解析，请尝试使用其他高速 DNS 服务器，例如 Google 的公共 DNS 服务器或 OpenDNS。\n\n2. 缓存 DNS 记录：在本地计算机上缓存 DNS 记录可以大大加快应用程序的响应。当您访问特定的网站时，计算机会自动缓存该网站的 DNS 记录。如果您再次访问该网站，则计算机将使用缓存的 DNS 记录。\n\n3. 减少 DNS 查找：当您访问一个网站时，您的计算机将会查找该域名的 IP 地址。如果网站有很多域名，则查找过程可能会变得非常缓慢。因此，尽可能使用较少的域名可以减少 DNS 查找的数量，并提高响应速度。\n\n4. 使用 CDN：CDN（内容分发网络）是一种将内容存储在全球多个位置的系统。这些位置通常都有专用的 DNS 服务器，可以大大加快站点的加载速度。\n\n5. 使用 DNS 缓存工具：一些辅助工具可以帮助您优化与 DNS 相关的设置，例如免费的 DNS Jumper 软件和 Namebench 工具，它们可以测试您的 DNS 响应时间并为您推荐最佳配置。\n\n通过使用高速 DNS 服务器、缓存 DNS 记录、减少 DNS 查找、使用 CDN 和 DNS 缓存工具等方法，可以显著提高 DNS 解析速度，从而加快应用程序响应时间。\n",{"_54":281,"_171":148,"_172":148,"_173":148,"_174":148,"_175":148,"_176":148,"_177":148,"_178":148,"_179":148},"https://api.github.com/repos/pro-collection/interview-question/issues/332/reactions","https://api.github.com/repos/pro-collection/interview-question/issues/332/timeline",{"_54":284,"_56":57,"_58":285,"_60":286,"_62":287,"_64":288,"_66":289,"_68":290,"_70":291,"_72":292,"_74":293,"_107":294,"_127":128,"_129":26,"_130":-5,"_131":296,"_133":297,"_155":148,"_149":299,"_151":300,"_154":-5,"_158":159,"_160":301,"_165":-5,"_166":302,"_168":303,"_180":305,"_182":-5,"_183":-5,"_184":185},"https://api.github.com/repos/pro-collection/interview-question/issues/297","https://api.github.com/repos/pro-collection/interview-question/issues/297/labels{/name}","https://api.github.com/repos/pro-collection/interview-question/issues/297/comments","https://api.github.com/repos/pro-collection/interview-question/issues/297/events","https://github.com/pro-collection/interview-question/issues/297",1673437110,"I_kwDOJGDC6c5jvp-2",297,"CDN 了解多少？【热度: 413】",{"_76":77,"_66":78,"_68":79,"_80":81,"_82":23,"_54":83,"_64":84,"_85":86,"_87":88,"_89":90,"_91":92,"_93":94,"_95":96,"_97":98,"_62":99,"_100":101,"_102":103,"_104":105,"_106":26},[295],{"_66":110,"_68":111,"_54":112,"_113":114,"_115":116,"_117":26,"_118":119},[],{"_54":206,"_64":207,"_58":208,"_66":209,"_68":210,"_70":211,"_72":212,"_118":213,"_143":298,"_145":215,"_147":148,"_127":128,"_149":216,"_151":217,"_153":-5,"_154":-5},{"_76":77,"_66":78,"_68":79,"_80":81,"_82":23,"_54":83,"_64":84,"_85":86,"_87":88,"_89":90,"_91":92,"_93":94,"_95":96,"_97":98,"_62":99,"_100":101,"_102":103,"_104":105,"_106":26},"2023-04-18T16:05:14Z","2023-04-23T13:11:12Z",{"_162":148,"_163":148,"_164":148},"### CDN 是什么\n\nCDN（Content Delivery Network）是指内容分发网络，它是由分布在不同地理位置的多台服务器组成的网络系统，用于更快地传递互联网内容和服务。CDN 可以缓存静态资源，加速用户访问速度，降低带宽消耗和服务器压力。\n\n1. CDN 的工作原理：CDN 通过将资源缓存在离用户更近的边缘节点，使用户可以更快地获取所需的内容。当用户访问一个包含 CDN 链接的网站时，CDN 会从最接近用户的节点返回内容。\n\n2. CDN 的优点：CDN 可以加速网站的加载速度、减轻源服务器的负载、提高网站的可用性和可靠性，同时还可以降低网络带宽使用和成本。\n\n3. CDN 的缓存策略：CDN 缓存可以采用不同的缓存策略，如时间戳策略、版本号策略、缓存控制策略等，以便尽可能地避免缓存出错或不及时更新。\n\n4. CDN 的常见问题：CDN 存在一些常见的问题，如缓存不一致、缓存雪崩、CDN 费用等。需要开发者和运维人员注意这些问题，并采取相应的解决方案。\n\n5. CDN 的选择：CDN 服务提供商众多，选择合适的 CDN 服务提供商需要考虑许多因素，如价格、性能、服务范围、支持的功能和协议等。\n\n6. CDN 的应用：CDN 被广泛应用于各种场景，如网站加速、视频点播、直播、在线游戏等。在实际应用中，需要根据具体场景来选择合适的 CDN 服务提供商和缓存策略，以达到最佳的效果。\n\n### CDN 预热\n\nCDN预热指在流量大涨之前，提前将资源缓存到CDN节点中，以加快用户请求响应速度，提高用户访问质量和稳定性的一种行为。通过提前将内容分发到CDN节点上，可以减少用户访问时由于第一次请求资源而导致的等待时间，从而提升用户的体验感受。一般来说，CDN预热是指在特定时间（如发布活动、重要通知等）前对资源进行CDN缓存的操作。预热完成后，用户请求相关资源时，就可以直接从CDN节点获取资源，而无需请求源站，从而提高网站的访问速度和稳定性。\n\n### CDN 刷新是什么\n\nCDN刷新指的是CDN缓存中的文件被更新后，需要将CDN服务器上缓存的旧文件清除，让其重新从源站拉取最新的内容，以保证CDN上的文件与源站文件保持一致。\n\n在网站更新或修改静态资源文件后，如果用户再次请求该文件，CDN服务器上的缓存仍然是旧版本的，用户就会访问到过时的文件，影响用户体验。为了解决这个问题，CDN提供了刷新服务，即将缓存的旧版本强制失效，让用户请求时可以快速访问到更新后的最新版本。\n\nCDN刷新通常有两种方式：\n\n1. 目录刷新：将某个目录下的所有文件都刷新，比较适用于网站进行大规模更新。\n\n2. 文件刷新：只将某个具体的文件刷新，比较适用于紧急情况下需要快速更新某个文件的情况。但由于刷新一次需要一定时间，因此刷新频率需要控制在合理的范围内，以避免影响CDN服务器性能和稳定性。\n\n### CDN 缓存策略有哪些\n\nCDN 缓存策略指的是在 CDN 服务器上缓存哪些资源以及缓存的有效期等相关规则。常见的 CDN 缓存策略有以下几种：\n\n1. 强制缓存：在资源的有效期内，浏览器每次请求该资源时，都直接从浏览器缓存中获取，不发送请求到服务器。可以通过设置响应头的 Cache-Control 和 Expires 字段实现。\n\n2. 协商缓存：在资源的有效期过期后，浏览器向服务器发起请求，并通过 If-Modified-Since 或者 If-None-Match 等字段验证资源是否有更新。如果资源未更新，服务器返回 304 Not Modified 响应，浏览器直接从本地缓存中获取资源。可以通过设置响应头的 Last-Modified 和 ETag 字段实现。\n\n3. CDN 边缘缓存：CDN 服务器缓存来自源站的资源，并将其分发给全球各地的用户。当用户请求某个资源时，CDN 服务器会根据缓存策略判断是否需要重新向源站请求资源。常见的缓存策略包括时间戳缓存、版本号缓存、目录级别缓存、参数级别缓存等。\n\n4. 客户端缓存：客户端缓存是指浏览器在本地缓存响应资源，下次请求该资源时可以直接从本地获取。可以通过设置响应头的 Cache-Control 和 Expires 字段实现。\n\n5. 源站缓存：源站缓存是指将静态资源放到应用服务器上缓存，在应用服务器上缓存的时间要短于 CDN 边缘缓存的时间。当 CDN 服务器的缓存过期或者未命中时，CDN 服务器会向源站发起请求获取最新的资源，并将其缓存到 CDN 服务器上。\n\n\n### 参考文档\n- https://juejin.cn/post/6913704568325046279\n- https://juejin.cn/post/7064952956201730062\n- https://juejin.cn/post/7166782260933296142\n",{"_54":304,"_171":148,"_172":148,"_173":148,"_174":148,"_175":148,"_176":148,"_177":148,"_178":148,"_179":148},"https://api.github.com/repos/pro-collection/interview-question/issues/297/reactions","https://api.github.com/repos/pro-collection/interview-question/issues/297/timeline",{"_54":307,"_56":57,"_58":308,"_60":309,"_62":310,"_64":311,"_66":312,"_68":313,"_70":314,"_72":315,"_74":316,"_107":317,"_127":128,"_129":26,"_130":-5,"_131":319,"_133":320,"_155":148,"_149":322,"_151":322,"_154":-5,"_158":159,"_160":323,"_165":-5,"_166":324,"_168":325,"_180":327,"_182":-5,"_183":-5,"_184":185},"https://api.github.com/repos/pro-collection/interview-question/issues/223","https://api.github.com/repos/pro-collection/interview-question/issues/223/labels{/name}","https://api.github.com/repos/pro-collection/interview-question/issues/223/comments","https://api.github.com/repos/pro-collection/interview-question/issues/223/events","https://github.com/pro-collection/interview-question/issues/223",1644213421,"I_kwDOJGDC6c5iALSt",223,"介绍下如何实现 token 加密？",{"_76":77,"_66":78,"_68":79,"_80":81,"_82":23,"_54":83,"_64":84,"_85":86,"_87":88,"_89":90,"_91":92,"_93":94,"_95":96,"_97":98,"_62":99,"_100":101,"_102":103,"_104":105,"_106":26},[318],{"_66":110,"_68":111,"_54":112,"_113":114,"_115":116,"_117":26,"_118":119},[],{"_54":135,"_64":136,"_58":137,"_66":138,"_68":139,"_70":140,"_72":141,"_118":142,"_143":321,"_145":146,"_147":148,"_127":128,"_149":150,"_151":152,"_153":-5,"_154":-5},{"_76":77,"_66":78,"_68":79,"_80":81,"_82":23,"_54":83,"_64":84,"_85":86,"_87":88,"_89":90,"_91":92,"_93":94,"_95":96,"_97":98,"_62":99,"_100":101,"_102":103,"_104":105,"_106":26},"2023-03-28T15:36:35Z",{"_162":148,"_163":148,"_164":148},"Token 是一种常用的身份验证机制，通常被用于 Web 应用程序的用户身份验证。Token 的生成和使用可以使用加密技术来增强安全性，下面介绍一下如何实现 Token 加密。\n\nToken 加密一般有两个步骤：\n\n1. 生成 Token\n2. 加密 Token\n\n### 1. 生成 Token\n\n在生成 Token 时，需要将用户的一些信息进行组合，生成一个字符串，该字符串通常包括以下信息：\n\n1. 用户的唯一标识（如用户 ID）\n2. 时间戳\n3. 有效期\n\n这些信息可以用分隔符分隔开，如用“.”分隔。\n\n### 2. 加密 Token\n\n加密 Token 有多种方式，下面介绍两种常用的方式：\n\n#### 1. 对称加密\n\n对称加密是指加密和解密使用同一密钥的加密算法。对称加密的优点是加解密速度快，缺点是密钥传输容易被截获，从而影响安全性。\n\n常用的对称加密算法有 DES、3DES、AES 等。\n\n#### 2. 非对称加密\n\n非对称加密是指加密和解密使用不同密钥的加密算法。非对称加密的优点是密钥传输安全，缺点是加解密速度较慢。\n\n常用的非对称加密算法有 RSA、DSA 等。\n\n一般情况下，为了兼顾安全性和效率，通常采用混合加密，即先使用非对称加密算法对 Token 进行加密，再使用对称加密算法对加密后的 Token 进行加密。\n\n综上所述，实现 Token 加密的关键在于对 Token 的生成和加密，需要根据具体业务需求来选择合适的加密算法和加密方式。",{"_54":326,"_171":148,"_172":148,"_173":148,"_174":148,"_175":148,"_176":148,"_177":148,"_178":148,"_179":148},"https://api.github.com/repos/pro-collection/interview-question/issues/223/reactions","https://api.github.com/repos/pro-collection/interview-question/issues/223/timeline",{"_54":329,"_56":57,"_58":330,"_60":331,"_62":332,"_64":333,"_66":334,"_68":335,"_70":336,"_72":337,"_74":338,"_107":339,"_127":128,"_129":26,"_130":-5,"_131":341,"_133":342,"_155":185,"_149":344,"_151":345,"_154":-5,"_158":159,"_160":346,"_165":-5,"_166":347,"_168":348,"_180":350,"_182":-5,"_183":-5,"_184":185},"https://api.github.com/repos/pro-collection/interview-question/issues/213","https://api.github.com/repos/pro-collection/interview-question/issues/213/labels{/name}","https://api.github.com/repos/pro-collection/interview-question/issues/213/comments","https://api.github.com/repos/pro-collection/interview-question/issues/213/events","https://github.com/pro-collection/interview-question/issues/213",1642380409,"I_kwDOJGDC6c5h5Lx5",213,"https 的证书验证过程是什么样的",{"_76":77,"_66":78,"_68":79,"_80":81,"_82":23,"_54":83,"_64":84,"_85":86,"_87":88,"_89":90,"_91":92,"_93":94,"_95":96,"_97":98,"_62":99,"_100":101,"_102":103,"_104":105,"_106":26},[340],{"_66":110,"_68":111,"_54":112,"_113":114,"_115":116,"_117":26,"_118":119},[],{"_54":206,"_64":207,"_58":208,"_66":209,"_68":210,"_70":211,"_72":212,"_118":213,"_143":343,"_145":215,"_147":148,"_127":128,"_149":216,"_151":217,"_153":-5,"_154":-5},{"_76":77,"_66":78,"_68":79,"_80":81,"_82":23,"_54":83,"_64":84,"_85":86,"_87":88,"_89":90,"_91":92,"_93":94,"_95":96,"_97":98,"_62":99,"_100":101,"_102":103,"_104":105,"_106":26},"2023-03-27T16:00:36Z","2023-09-16T16:59:45Z",{"_162":148,"_163":148,"_164":148},"HTTPS的证书验证过程通常包括以下几个步骤：\n\n1. 客户端向服务端发起HTTPS请求，服务端将其公钥证书发送给客户端。\n2. 客户端接收到服务端的证书后，首先验证证书是否过期，如果过期，则证书无效，验证失败；如果证书未过期，则进行下一步。\n3. 客户端使用CA证书（如系统内置的或者从服务端获取）对服务端证书进行验证，以确定该证书是否是由受信任的CA颁发的。如果验证失败，则证书无效，验证失败；如果验证成功，则进行下一步。\n4. 客户端生成一个随机值，使用服务端公钥进行加密，并将加密后的随机值发送给服务端。\n5. 服务端接收到客户端的随机值后，使用私钥进行解密，得到随机值。服务端再将随机值作为密钥，使用对称加密算法加密需要传输的数据，并发送给客户端。\n6. 客户端接收到服务端发送的加密数据后，使用随机值进行解密，得到明文数据。\n\n以上就是HTTPS证书验证的一般流程。客户端验证服务端证书的方式是通过验证证书的数字签名来确定证书的合法性，如果数字签名验证失败，则证书无效，验证失败。",{"_54":349,"_171":148,"_172":148,"_173":148,"_174":148,"_175":148,"_176":148,"_177":148,"_178":148,"_179":148},"https://api.github.com/repos/pro-collection/interview-question/issues/213/reactions","https://api.github.com/repos/pro-collection/interview-question/issues/213/timeline",{"_54":352,"_56":57,"_58":353,"_60":354,"_62":355,"_64":356,"_66":357,"_68":358,"_70":359,"_72":360,"_74":361,"_107":362,"_127":128,"_129":26,"_130":-5,"_131":369,"_133":370,"_155":185,"_149":372,"_151":373,"_154":-5,"_158":159,"_160":374,"_165":-5,"_166":375,"_168":376,"_180":378,"_182":-5,"_183":-5,"_184":185},"https://api.github.com/repos/pro-collection/interview-question/issues/206","https://api.github.com/repos/pro-collection/interview-question/issues/206/labels{/name}","https://api.github.com/repos/pro-collection/interview-question/issues/206/comments","https://api.github.com/repos/pro-collection/interview-question/issues/206/events","https://github.com/pro-collection/interview-question/issues/206",1640932956,"I_kwDOJGDC6c5hzqZc",206,"浏览器缓存中 Memory Cache 和 Disk Cache，有啥区别？",{"_76":77,"_66":78,"_68":79,"_80":81,"_82":23,"_54":83,"_64":84,"_85":86,"_87":88,"_89":90,"_91":92,"_93":94,"_95":96,"_97":98,"_62":99,"_100":101,"_102":103,"_104":105,"_106":26},[363,364],{"_66":110,"_68":111,"_54":112,"_113":114,"_115":116,"_117":26,"_118":119},{"_66":365,"_68":366,"_54":367,"_113":368,"_115":125,"_117":26,"_118":126},5312712328,"LA_kwDOJGDC6c8AAAABPKmOiA","https://api.github.com/repos/pro-collection/interview-question/labels/%E5%AD%97%E8%8A%82%E8%B7%B3%E5%8A%A8","字节跳动",[],{"_54":135,"_64":136,"_58":137,"_66":138,"_68":139,"_70":140,"_72":141,"_118":142,"_143":371,"_145":146,"_147":148,"_127":128,"_149":150,"_151":152,"_153":-5,"_154":-5},{"_76":77,"_66":78,"_68":79,"_80":81,"_82":23,"_54":83,"_64":84,"_85":86,"_87":88,"_89":90,"_91":92,"_93":94,"_95":96,"_97":98,"_62":99,"_100":101,"_102":103,"_104":105,"_106":26},"2023-03-26T14:24:33Z","2023-04-12T13:47:16Z",{"_162":148,"_163":148,"_164":148},"### Memory Cache 和 Disk Cache 的区别\r\n\r\n在浏览器缓存中，Memory Cache 和 Disk Cache 是两种不同的缓存类型，它们有以下区别：\r\n\r\n1. 存储位置：Memory Cache 存储在内存中，而 Disk Cache 存储在硬盘中。\r\n2. 读取速度：Memory Cache 读取速度比 Disk Cache 快，因为内存访问速度比硬盘访问速度快。\r\n3. 存储容量：Memory Cache 存储容量比较小，一般只有几十兆，而 Disk Cache 存储容量比较大，可以有数百兆或者更多。\r\n4. 生命周期：Memory Cache 生命周期短暂，一般只在当前会话中有效，当会话结束或者浏览器关闭时，Memory Cache 就会被清空；而 Disk Cache 生命周期比较长，数据可以被保存很长时间，即使浏览器关闭了，下次打开还可以使用。\r\n\r\n一般来说，浏览器在请求资源时，会优先从 Memory Cache 中读取，如果没有找到再去 Disk Cache 中查找。如果两种缓存中都没有找到，则会向服务器发送请求。如果需要强制刷新缓存，可以通过清空浏览器缓存来实现。\r\n\r\n### 什么情况下资源会缓存在 Memory Cache，什么情况下会缓存在 Disk Cache ?\r\n\r\n浏览器中的缓存是为了提高网页访问速度和减少网络流量而存在的。缓存分为 Memory Cache 和 Disk Cache 两种。\r\n\r\nMemory Cache 是浏览器内存缓存，资源会被缓存在内存中，由于内存读取速度快，所以 Memory Cache 的读取速度也较快。资源被缓存在 Memory Cache 中的情况有：\r\n\r\n1. 当前页面中通过或者