Describe the bug

1. a new vite app: default port is 3000
   

2. my koa server: this port is also 3000
   

when I start vite app and then start koa server OR start koa server and then start vite app, no indication of port conflict.

And I use Google Chrome to access the page 127.0.0.1:3000, the page display content about the latter server content.

Reproduction

This question reminds me of PM2——master-slave mode, but vite didn't handle it well. I try to read the vite's source code, but I am worried about misunderstanding, so come here to issue. If this is a problem, can you provide solutions or fix it as soon as possible?

thanks.

System Info

@vite:   2.6.4,
@node:   14.16.0,
@koa:    2.13.3,
@Google: Chrome: 94.0.4606.71 (official version) (x86_64),
@OS: 	 macOS Catalina 10.15.7,
@JavaScript:	V8 9.4.146.18,

Used Package Manager

npm

Logs

null

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to https://github.com/vuejs/vue-next instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.