docker-port-forward-shadow-debug

What problem does it solve?

This Skill resolves the common issue where Docker containers expose ports 80 or 443 to the host, shadowing directly running host services like nginx, which causes reverse proxy traffic to be intercepted by the wrong process, leading to unexpected server response headers, 404 errors, or misrouted API requests.

Core Features & Use Cases

• Step-by-Step Diagnostic Checklist: Commands to verify actual serving processes via HTTP headers, locate conflicting Docker containers, and identify port mapping configurations.
• Temporary and Permanent Fix Guidance: Instructions to kill shadow processes for immediate testing and update Docker configurations to eliminate port conflicts long-term.
• Clarification of Misleading Tool Output: Explains why tools like ss may show incorrect listener information when Docker port forwarding is active.
• Real-World Use Case: If your nginx reverse proxy returns unexpected server: Caddy headers, this Skill helps you trace the issue to a Docker container running Caddy with a -p 443:443 port mapping.

Quick Start

Use the docker-port-forward-shadow-debug skill to identify and fix Docker containers that are shadowing your host's reverse proxy ports 80 or 443.