单主机多Web服务未指定端口时的数据包正确投递疑问

Hey there! Let's break this down step by step—it's a super common gotcha when running multiple services on one machine.

First, let's nail down the basics: when you type a URL without a port (like http://your-server-ip or http://your-domain.com), your browser doesn't just guess which port to use. It automatically uses the default port for the protocol you're accessing: port 80 for plain HTTP, port 443 for HTTPS.

So here's the first scenario: if your two web servers are only listening on ports 1200 and 1201, and nothing on your machine is listening on port 80/443, any client request without a port will get rejected immediately. Your server's TCP stack will see the packet is destined for port 80/443, notice no process is waiting for traffic there, and send a "connection refused" response back to the client. Those requests will never reach your 1200/1201 servers at all.

If you want clients to reach either service without typing a port, you need a middleman: a reverse proxy (think Nginx, Apache, or Caddy). Here's how that works:

• Set up the reverse proxy to listen on port 80 (or 443 for HTTPS)—the default ports browsers automatically use.
• When a client sends a request to your server's IP/domain without a port, it lands at the reverse proxy first.
• The proxy uses rules you define to forward the request to the correct backend server (1200 or 1201). These rules can be based on:
  • The domain name in the request (e.g., service1.yourdomain.com routes to 1200, service2.yourdomain.com routes to 1201)
  • The URL path (e.g., yourdomain.com/service1 forwards to 1200, yourdomain.com/service2 forwards to 1201)
  • Other request headers or attributes

To clarify the port detail you mentioned: you're right that incoming packets include the client's IP and source port (which helps your server send responses back to the correct browser tab/process). But for delivering the packet to the right server process on your machine, the destination port in the packet is what matters. If that destination port doesn't match any listening process, the packet gets dropped or rejected.

So to wrap up: without a reverse proxy listening on the default port, clients can't reach your non-default port services without explicitly typing the port. With a reverse proxy, you can route requests to the right backend service based on other request details—even when no port is included in the URL.

备注：内容来源于stack exchange，提问作者user3103957