This is a follow up to my old post from 2018: Upgrade Postgres Container to Version 10
In the meanwhile, I upgraded every year my Docker containers to the newest version of Postgres and realized, I can further optimize that process. But first, let's take a step back. Why not just pull the latest image and mount the existing directory? This works with minor version upgrades, but not major ones. If you do this with a major version upgrade, you'll see the following error:
FATAL: database files are incompatible with server
DETAIL: The data directory was initialized by PostgreSQL version 9.6, which is not compatible with this version 10.2.
These are the new step-by-step upgrade instructions:
For sake of simplicity, I assume the following things:
- You are using either the official Postgres docker image or an image similar in configuration.
- You are mounting
/var/lib/postgresql/dataonto your disc.
- Stop any application accessing the database, you want to do this, to guarantee a consistent state.
- Create a dump using
docker exec POSTGRES_CONTAINER pg_dumpall -U postgres > dump.sql. This will be stored on your local disc, so you'll be safe to stop and possibly remove the container.
- Stop the container. Optionally, back up the directory, after you stopped the container.
- Start the new container using the new Postgres image. I prefer to mount a new directory for the data. In case you want to reuse the same directory, make sure you created a backup in step 3. The mounted directory must be empty, otherwise, you'd see the aforementioned error message in the docker logs, and the container would be crashing.
- I assume the new Postgres container is successfully up and running, but empty. So we need to import the data again. To do this, simply run
docker exec -i POSTGRES_CONTAINER psql -U postgres < dump.sql
- Now you can start the application again, and your upgrade should be complete.