How a Docker Daemon Restart Silently Broke a Reverse Proxy Network

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A developer installing k3s on a memory-constrained server triggered a chain of unintended consequences after restarting the Docker daemon to diagnose a container networking failure. The restart reassigned IP addresses to containers on an unrelated network, including a reverse proxy and a gateway service that lacked static IP configurations. The reverse proxy was configured to allow only two sources — the VPS's public IP and a specific Docker-network address — meaning any address change would silently block all gated services. Investigation revealed that the Docker-network address hardcoded in the proxy's access rules no longer matched the container that had moved after the restart. The incident highlighted how a single dynamic IP assignment, with no static address pinned, can cascade into a full service outage that appears unrelated to its actual cause.

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