Kamal is my go-to deployment tool for Rails apps — it handles SSL, zero-downtime deploys, and the proxy with a single kamal deploy command. But officially, Kamal expects you to build and push your own image. It can't deploy an arbitrary public image directly from a registry like Docker Hub or GHCR.

Or so I thought.

In this post, I'll show you a small trick using a placeholder Dockerfile + Kamal accessories to deploy any publicly available Docker image to a VPS — no custom build required.

The Problem

Sometimes you just want to run a pre-built public image on your server.…