This is a PoC for using pg_upgrade inside Docker -- learn from it, adapt it for your needs; don't expect it to work as-is!
(Source for this image is available at https://github.com/tianon/docker-postgres-upgrade.)
Tags of this image are of the format OLD-to-NEW, where OLD represents the version of PostgreSQL you are currently running, and NEW represents the version of PostgreSQL you would like to upgrade to.
In order to get good performance, it is recommended to run this image with docker run image --link (see pg_upgrade documentation for more details).
For this to be feasible, your directory structure should look something like this: (if yours does not, either adjust it, or scroll down to see the alternate pattern for running this image)
$ find DIR -mindepth 2 -maxdepth 2
DIR/OLD/docker
DIR/NEW/docker
$ docker run --rm \
--mount 'type=bind,src=DIR,dst=/var/lib/postgresql' \
--env 'PGDATAOLD=/var/lib/postgresql/OLD/docker' \
--env 'PGDATANEW=/var/lib/postgresql/NEW/docker' \
tianon/postgres-upgrade:OLD-to-NEW \
--link
...More concretely, assuming OLD of 17, NEW of 18, and DIR of /mnt/bigdrive/postgresql:
$ find /mnt/bigdrive/postgresql -mindepth 2 -maxdepth 2
/mnt/bigdrive/postgresql/17/docker
/mnt/bigdrive/postgresql/18/docker
$ docker run --rm \
--mount 'type=bind,src=/mnt/bigdrive/postgresql,dst=/var/lib/postgresql' \
--env 'PGDATAOLD=/var/lib/postgresql/17/docker' \
--env 'PGDATANEW=/var/lib/postgresql/18/docker' \
tianon/postgres-upgrade:17-to-18 \
--link
...(as in, your previous postgres:17 instance was running with -v /mnt/bigdrive/postgresql/17/docker:/var/lib/postgresql/data, and your new postgres:18 instance will run with -v /mnt/bigdrive/postgresql:/var/lib/postgresql, which is explicitly accounting for docker-library/postgres#1259)
If your two directories (denoted below as PGDATAOLD and PGDATANEW) do not follow this structure, then the following may also be used (but will be slower):
$ docker run --rm \
--mount 'type=bind,src=PGDATAOLD,dst=/var/lib/postgresql/OLD/docker' \
--mount 'type=bind,src=PGDATANEW,dst=/var/lib/postgresql/NEW/docker' \
--env 'PGDATAOLD=/var/lib/postgresql/OLD/docker' \
--env 'PGDATANEW=/var/lib/postgresql/NEW/docker' \
tianon/postgres-upgrade:OLD-to-NEW
...More concretely, assuming OLD of 17, NEW of 18, PGDATAOLD of /mnt/bigdrive/postgresql-17, and PGDATANEW of /mnt/bigdrive/postgresql-18:
$ docker run --rm \
--mount 'type=bind,src=/mnt/bigdrive/postgresql-17,dst=/var/lib/postgresql/17/docker' \
--mount 'type=bind,src=/mnt/bigdrive/postgresql-18,dst=/var/lib/postgresql/18/docker' \
--env 'PGDATAOLD=/var/lib/postgresql/17/docker' \
--env 'PGDATANEW=/var/lib/postgresql/18/docker' \
tianon/postgres-upgrade:17-to-18
...(which assumes that your previous postgres:17 instance was running with -v /mnt/bigdrive/postgresql-17:/var/lib/postgresql/data, and your new postgres:18 instance will run with -v /mnt/bigdrive/postgresql-18:/var/lib/postgresql/18/docker, although that's not recommended)
Putting it all together:
$ mkdir -p postgres-upgrade-testing
$ cd postgres-upgrade-testing
$ OLD='17'
$ NEW='18'
$ docker run -dit \
--name postgres-upgrade-testing \
--env POSTGRES_PASSWORD='password' \
--env POSTGRES_INITDB_ARGS='--data-checksums' \
--mount "type=bind,src=$PWD,dst=/var/lib/postgresql" \
--env PGDATA="/var/lib/postgresql/$OLD/docker" \
--pull always \
"postgres:$OLD"
$ sleep 5
$ docker logs --tail 100 postgres-upgrade-testing
$ # let's get some testing data in there
$ docker exec -it \
-u postgres \
postgres-upgrade-testing \
pgbench -i -s 10
$ docker stop postgres-upgrade-testing
$ docker rm postgres-upgrade-testing
$ docker run --rm \
--env POSTGRES_INITDB_ARGS='--data-checksums' \
--mount "type=bind,src=$PWD,dst=/var/lib/postgresql" \
--env "PGDATAOLD=/var/lib/postgresql/$OLD/docker" \
--env "PGDATANEW=/var/lib/postgresql/$NEW/docker" \
--pull always \
"tianon/postgres-upgrade:$OLD-to-$NEW" \
--link
$ docker run -dit \
--name postgres-upgrade-testing \
--env POSTGRES_PASSWORD='password' \
--env POSTGRES_INITDB_ARGS='--data-checksums' \
--mount "type=bind,src=$PWD,dst=/var/lib/postgresql" \
--env PGDATA="/var/lib/postgresql/$NEW/docker" \
--pull always \
"postgres:$NEW"
$ sleep 5
$ docker logs --tail 100 postgres-upgrade-testing
$ # can now (probably) safely remove "$OLD"
$ sudo rm -rf "$OLD"
