Docker Postgres Data Persistence

My Docker-based app is already up and running and builds automatically from GitHub using render. Postgres is the database, and everything works—until a new image is deployed. Each push wipes the data because I have not yet introduced a proper persistence strategy. I do not use Kubernetes or Swarm; it is a single-container setup built the straightforward Docker way.

What I need is clear, hands-on guidance that leaves me with a repeatable solution: the database must survive container restarts, re-builds, and new pushes from GitHub. I am not sure whether Docker volumes are configured correctly (or at all), so feel free to start there and propose the best practice—named volumes, bind mounts, or an alternative that fits a simple Docker workflow.

Deliverables
• Updated Dockerfile and/or docker-compose.yml (if compose is recommended) showing the persistent storage configuration
• Step-by-step notes or a short README so I can reproduce the setup on future projects
• One quick test to confirm data remains intact after a fresh build and container restart

The goal is to walk away confident that my Postgres data is safe every time the image is rebuilt and redeployed from GitHub.