Howto Upgrade Postgres (in Docker)

This process has downtime. Using docker-compose in this scenario.

1. Dump the database (pg_dumpall --user postgres > dump10.1-2020-06-04.sql, or user root)
2. docker-compose down
3. Back up physical files (only needed if everything goes to hell - tar -cvpzf postgresfiles10.1-2020-06-04.tar.gz /var/lib/path-to-db-files)
4. UPGRADE POSTGRES VERSION IN DOCKER-COMPOSE.YML
5. docker-compose up db (start only db container, not other stuff)
6. Another terminal docker exec -it hash-of-db-container /bin/bash (find out hash with docker ps)
7. cat data/dump10.1-2020-06-04.sql | psql --user postgres - load dump to newer version of postgres
8. Stop it and run the whole app

Detailed info https://www.postgresql.org/docs/10/upgrading.html.