---
title: Web Service Port
url: "/docs/debug/web-server-port/"
canonical_url: https://docs.blossom88.com/docs/debug/web-server-port/
markdown_url: https://docs.blossom88.com/docs/debug/web-server-port.md
summary: Fix public Services that do not listen on the assigned port
categories:
- debugging
- configuration
- troubleshooting
---

# Web Service Port

A public Service must listen on `0.0.0.0` and the port Blossom supplies in
`$PORT`. Binding only to `127.0.0.1` or hardcoding another port prevents health
checks and public routing from reaching the process.

## Symptoms

- the Service remains `starting` or `unhealthy`
- health checks report connection refused
- the application logs one listening port while the Service expects another
- the generated or custom Domain does not reach an otherwise successful Build

## Diagnose

1. Check the Service logs for its bind address and port.
2. Confirm the Service command does not override `$PORT`.
3. Open a Container shell with `blossom shell` if the runtime needs interactive
   inspection.
4. Correct the application or Service command, then deploy a new Release.

## Framework Examples

### Node.js And Express

```javascript
const port = process.env.PORT || 3000;
app.listen(port, "0.0.0.0");
```

### Ruby And Rails

```ruby
port ENV.fetch("PORT", 3000)
bind "tcp://0.0.0.0:#{ENV.fetch('PORT', 3000)}"
```

### Python And Flask

```python
import os
app.run(host="0.0.0.0", port=int(os.environ.get("PORT", 5000)))
```

Changing Domain settings does not fix an incorrect application bind. The
Service contract is the stable fix.