一个请求的始末 The Beginning and End of a Request

1. DNS
   1. root dns
   2. TLD top-level domain
   3. authority domain server
   4. recursive domain server: The 1.1.1.1 in cloudfare
2. ARP（Address Resolution Protocol，地址解析协议）是用来将IP地址解析为MAC地址的协议。主机或三层网络设备上会维护一张ARP表，用于存储IP地址和MAC地址的映射关系，一般ARP表项包括动态ARP表项和静态ARP表项。
3. HTTP
   1. 认证 Authentication
   2. 授权 Authorization
   3. 凭证 Credentail
   4. 保密 Confidentiality
   5. 传输 Transport Security
   6. 验证 Verification
   7. 审计 Audit
   8. Cookie
      1. client cache
      2. server cache
5. CDN
6. NGINX reverse proxy
7. Http server
8. tcp server
9. rpc server
   1. service mesh
   2. observability
      1. metrics
      2. tracing
      3. Logging