Codespaces: private port forwarding fails while another private port works

[firstjuregg-svg]

🏷️ Discussion Type

Question

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In an existing Codespace using VS Code web, private port 16031 works. A separate Vite process listened on 127.0.0.1:16032 and returned HTTP 200 for /login locally.

One attempt to forward localhost:16032 failed. The UI reported that the host might be unavailable or the port already forwarded. No 16032 entry appeared in PORTS.

An official Codespaces log export did not establish a specific refusal code or root cause. The new Vite process was stopped; the working preview was preserved.

What minimal, non-destructive recovery is recommended without rebuilding the Codespace, interrupting the working preview, or making any port public?

[nikomarinovic]

I’d try adding port 16032 manually from the PORTS tab first. Make sure nothing else is using it, then enter 16032 under Add Port and keep its visibility set to Private. No need to rebuild or restart the Codespace, especially since the existing preview is working. If it still fails, I’d leave the working setup alone and check GitHub’s port forwarding troubleshooting docs before trying anything more disruptive.

https://docs.github.com/en/codespaces/troubleshooting/troubleshooting-port-forwarding-for-github-codespaces

[sapuCodes]

Hey @firstjuregg-svg, I’ve run into similar things. Here are some safe things to try that won’t touch your working preview:

1. Add the port from the PORTS tab. Click “Add Port”, type 16032 and press Enter. This sometimes works when typing localhost:16032 fails.

2. Try the CLI instead of the UI. In a terminal, run:

gh codespace ports -c <your-codespace-name>

If 16032 shows up as stale or stuck, you can remove it there and add it again.

3. Reload the VS Code web window. Press Ctrl+Shift+P and run “Developer: Reload Window”. This only refreshes the editor, not the Codespace, so your running processes and the working port stay up. It often clears the “already forwarded” state.

4. Make Vite listen on all interfaces. Run it with vite --host (or set server.host: true in vite.config), since binding only to 127.0.0.1 can cause trouble. Newer Vite versions can also block the forwarded URL, so you may need to add it to server.allowedHosts.

5. Check the port is really listening:

   ss -ltnp | grep 16032

If none of this works, try a different port number (like 5173) for the second app. That avoids the stuck 16032 entry without touching the working one.

Hope this helps!