Docker Expose Port 81

Expose Port 81 in Docker

docker run -p 81:81 your-image-name
		

This command maps container port 81 to the same port on the host machine.

Dockerfile Example

FROM node:18-alpine
WORKDIR /app
COPY . .
EXPOSE 81
CMD ["npm", "start"]
		

The EXPOSE instruction documents that the container listens on port 81.

EXPOSE vs Publish (-p)

• EXPOSE 81 documents the port inside the container.
• -p 81:81 makes the port accessible from the host.
• Exposed ports are not reachable unless published.

Docker Expose Port 81 Not Working

If Docker expose port 81 is not working, it is usually due to incorrect port publishing, an application not listening on the expected port, or a port conflict on the host machine.

Port 81 Already in Use

The error “port 81 already in use” means another process is already bound to that port on your host system.

# Find process using port 81
lsof -i :81

# OR use a different host port
docker run -p 8080:81 your-image-name
		

• Ensure your app is listening on port 81 inside the container
• Verify the port is published using -p
• Check firewall or network rules
• Avoid conflicts with existing services

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