Vite proxy does not work in Docker environment

[scriptPilot]

Describe the bug

I would like to run both, backend and frontend in Docker.

Backend is running in php:apache container, exposing /api.php at localhost:8000.
Frontend is running node container, exposing vite server at localhost:5173.

Vite proxy config:

{
  "/api.php": "http://localhost:8000"
}

When I run the backend in Docker and frontend without, it works like a charm.

When I run both with Docker, the frontend is accessible and the backend too, but the call from frontend via proxy to the backend does not work with fetch().

Reproduction

https://github.com/scriptPilot/bug-vite-proxy

Steps to reproduce

See readme in the repo.

System Info

From Docker:


  System:
    OS: Linux 5.10 Debian GNU/Linux 12 (bookworm) 12 (bookworm)
    CPU: (6) arm64 unknown
    Memory: 2.91 GB / 3.84 GB
    Container: Yes
    Shell: 5.2.15 - /bin/bash
  Binaries:
    Node: 18.18.2 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 9.8.1 - /usr/local/bin/npm
  npmPackages:
    vite: ^4.5.0 => 4.5.0 

### Used Package Manager

npm

### Logs

_No response_

### Validations

- [X] Follow our [Code of Conduct](https://github.com/vitejs/vite/blob/main/CODE_OF_CONDUCT.md)
- [X] Read the [Contributing Guidelines](https://github.com/vitejs/vite/blob/main/CONTRIBUTING.md).
- [X] Read the [docs](https://vitejs.dev/guide).
- [X] Check that there isn't [already an issue](https://github.com/vitejs/vite/issues) that reports the same bug to avoid creating a duplicate.
- [X] 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 [vuejs/core](https://github.com/vuejs/core) instead.
- [X] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/vitejs/vite/discussions) or join our [Discord Chat Server](https://chat.vitejs.dev/).
- [X] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.

[scriptPilot]

I was able to solve this issue with support of this thread:
https://stackoverflow.com/questions/74281247/api-call-not-reaching-vite-proxy-target-localhost5000

Solution: Use the PHP Docker container name + internal port

proxy: {
  '/api.php': 'http://php:80'
}