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Docker Networking Demystified: Bridges, DNS, and the localhost Pitfall

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Docker containers communicate through virtual network switches, but the legacy default bridge lacks DNS resolution between containers, making named networks essential for reliable service discovery. User-defined networks, automatically created by Docker Compose per project, enable containers to reach each other by service name. A common misconfiguration occurs when an app inside a container binds to 127.0.0.1, making it unreachable even when ports are published, because port forwarding targets the container's external interface. To ensure published ports work correctly, containerized servers must listen on 0.0.0.0 instead of localhost. Understanding the distinction between the 'ports' and 'expose' directives, along with proper network configuration, is key to avoiding connectivity issues in containerized environments.

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Docker Networking Demystified: Bridges, DNS, and the localhost Pitfall · ShortSingh