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Docker Ports

EXPOSE vs Publish (-p)

# Dockerfile - EXPOSE documents the port (metadata only)
EXPOSE 3000

# -p actually publishes/maps the port
docker run -p 8080:3000 myapp

Port Mapping Options

# Map to specific host port
docker run -p 8080:80 nginx

# Map to random host port
docker run -p 80 nginx
docker run -P nginx  # Publish all exposed ports

# Map to specific interface
docker run -p 127.0.0.1:8080:80 nginx

# Map UDP port
docker run -p 53:53/udp dns-server

# Map port range
docker run -p 8080-8085:80-85 myapp

Checking Port Mappings

# See port mappings
docker port container_name

# Example output:
# 80/tcp -> 0.0.0.0:8080
# 443/tcp -> 0.0.0.0:8443

Port Best Practices

Bind to 127.0.0.1 for local-only access
Use random ports in development to avoid conflicts
Don't expose database ports publicly
Use reverse proxy for production

# Secure: Only accessible locally
docker run -p 127.0.0.1:5432:5432 postgres

# Insecure: Accessible from anywhere
docker run -p 5432:5432 postgres