Docker Expose Port 804

Expose Port 804 in Docker

docker run -p 804:804 your-image-name
		

This command maps container port 804 to the same port on the host machine.

Dockerfile Example

FROM node:18-alpine
WORKDIR /app
COPY . .
EXPOSE 804
CMD ["npm", "start"]
		

The EXPOSE instruction documents that the container listens on port 804.

EXPOSE vs Publish (-p)

• EXPOSE 804 documents the port inside the container.
• -p 804:804 makes the port accessible from the host.
• Exposed ports are not reachable unless published.

Docker Expose Port 804 Not Working

If Docker expose port 804 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 804 Already in Use

The error “port 804 already in use” means another process is already bound to that port on your host system.

# Find process using port 804
lsof -i :804

# OR use a different host port
docker run -p 8080:804 your-image-name
		

• Ensure your app is listening on port 804 inside the container
• Verify the port is published using -p
• Check firewall or network rules
• Avoid conflicts with existing services

Related Docker Expose Port Guides