08 Replace a container, keep its data

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Goal

Recreate db so it also publishes port 5432, keeping the same image, password and pgdata volume — and the data in it.

You can't add a port, a variable or a mount to an existing container. You replace it. That sounds alarming until you've moved the state into a volume — then the container is disposable and replacing it is routine.

This is the core habit of working with containers: treat them as cattle, not pets, and keep anything precious in volumes.

Try it

Recreate the database with a published port and check the data survived.

Don't try to "upgrade" by swapping postgres:16 for postgres:17 on the same volume — try it and read the logs. Major versions need a real migration (pg_upgrade or a dump and restore).

Go to the terminal

Hint

docker rm -f db, then run it again exactly as before plus -p 5432:5432.

Show a solution

docker inspect db
docker rm -f db
docker run -d --name db -e POSTGRES_PASSWORD=secret -v pgdata:/var/lib/postgresql/data -p 5432:5432 postgres:16
docker exec db ls /var/lib/postgresql/data

This interactive environment needs JavaScript. Everything you need to read is on this page, and the solution works the same way for real.

Docker

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