---
title: Understanding the Port parameter
description: Learn about the Port parameter and the PORT environment variable in Scaleway Serverless Containers.
tags: port variable environment containers serverless
dates:
validation: 2025-10-21
posted: 2025-04-02
---
## Port parameter
The port of a containerized application refers to the network port that the application inside the container listens on for incoming requests.
When you deploy a container, you must map this internal port to a port on the host machine by specifying its value at [container creation](/serverless-containers/how-to/deploy-container/) via the **Port** parameter. The value defined in this parameter will then be passed to your container during the deployment inside the `PORT` environment variable.
- Only one port can be exposed per Serverless Container.
- Your container is accessible from the internet via ports 80 and 443, regardless of the specified port. The value you set determines how the Scaleway infrastructure accesses your container.
## PORT environment variable
To allow you application to be reachable, the port declared as a parameter when [creating your Container](/serverless-containers/how-to/deploy-container/) must be the same as the port exposed by your containerized application.
We therefore recommend you use the `$PORT` variable in your application, as it will contain the port parameter value, as shown in the examples below.
### nginx example
```dockerfile
FROM nginx:alpine
# Create a minimal nginx config that will be modified at runtime
RUN echo 'worker_processes 1; \
events { worker_connections 1024; } \
http { \
server { \
listen REPLACE_PORT default_server; \
location / { return 200 "Hello from Nginx on Scaleway Serverless Containers!\n"; } \
} \
}' > /etc/nginx/nginx.conf
# Simple startup script that replaces the port
CMD ["/bin/sh", "-c", "sed -i s/REPLACE_PORT/$PORT/g /etc/nginx/nginx.conf && exec nginx -g 'daemon off;'"]
```
### NodeJS example
```dockerfile
# Use the official Node.js slim image
FROM node:22-slim
# Create app directory
WORKDIR /usr/src/app
# Create package.json and simple Express app directly in Dockerfile
RUN echo '{"name":"scaleway-serverless","version":"1.0.0","description":"","main":"server.js","scripts":{"start":"node server.js"},"dependencies":{"express":"^5"}}' > package.json && \
npm install && \
echo "const express = require('express');\nconst app = express();\nconst port = process.env.PORT || 8080;\n\napp.get('/', (req, res) => {\n res.send('Hello from Scaleway Serverless!
');\n});\n\napp.listen(port, () => {\n console.log(`Server running on port \${port}`);\n});" > server.js
# Start the application
CMD ["npm", "start"]
```
### Python Flask example
```dockerfile
# Use the official Python slim image
FROM python:3.13-slim
# Install Flask
RUN pip install flask gunicorn
# Create a simple Flask app directly in the Dockerfile
RUN echo "from flask import Flask\napp = Flask(__name__)\n\n@app.route('/')\ndef hello():\n return 'Hello from Flask on Scaleway Serverless!
'\n\nif __name__ == '__main__':\n app.run(host='0.0.0.0', port=8080)" > app.py
# Run the app with Gunicorn
CMD exec gunicorn --bind :$PORT --workers 1 --threads 8 app:app
```