Docker Expose Port 651

Expose Port 651 in Docker

docker run -p 651:651 your-image-name
		

This command maps container port 651 to the same port on the host machine.

Dockerfile Example

FROM node:18-alpine
WORKDIR /app
COPY . .
EXPOSE 651
CMD ["npm", "start"]
		

The EXPOSE instruction documents that the container listens on port 651.

EXPOSE vs Publish (-p)

• EXPOSE 651 documents the port inside the container.
• -p 651:651 makes the port accessible from the host.
• Exposed ports are not reachable unless published.

Docker Expose Port 651 Not Working

If Docker expose port 651 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 651 Already in Use

The error “port 651 already in use” means another process is already bound to that port on your host system.

# Find process using port 651
lsof -i :651

# OR use a different host port
docker run -p 8080:651 your-image-name
		

• Ensure your app is listening on port 651 inside the container
• Verify the port is published using -p
• Check firewall or network rules
• Avoid conflicts with existing services

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