Rip & Tear: PostgreSQL Surgery

After taking a leap of faith and upgrading my past-EOL Alpine Linux server to the latest-stable release and packages, I was rewarded with an almost seamless upgrade. Thanks to my dockerized personal infrastructure, all my personal services came right back up without a hitch - apart from two that depended on a local PostgreSQL database.

Yes, I was stupid to try and save resources by having a few containers all depend on a local install of Postgres - but now I was in a real pickle. Alpine had installed version 17 of PostgreSQL, and my database was stuck way back on 13 - plus the binary had been purged. To no avail, I attempted to use apk to install from the older repository, but a dependency clash ensued.

Docker to the rescue. If I couldn’t run Postgres 13 natively, I imagined I could spin up a Docker container and point it towards the original data to successfully run pg_dump and save the data. After a little bit of copying and chown-ing from /etc/postgresql (symlinks btfo) and /var/lib/postgresql/13/data, I was right back where I started, and all my services were happy again, no longer screaming “no db! NO DB! NO DB!!!”

Here’s my docker-compose recipe:

services:
  postgres13:
    image: postgres:13.12
    #^ The version you are trying to rescue data from
    restart: unless-stopped
    ports:
      - 5432:5432
    environment:
      PGDATA: /data
      #^ Point the database to your bound volume
    volumes:
      - type: bind
        source: /home/the-service-username/postgres-data
        target: /data
        #^ Allow the container to see your data on disk

From here I was happily able to pg_dump the data and migrate normally to a properly secured database.

Good times were had by all.

                                           Not possible
                                             to extract data
                                                 ^
                                                 |
  +----------------------------------------------+------------+
  | Host: Alpine Linux                           |            |
  |                                              |            |
  |              .m.+-             Postgres 13   |            |
  |             m-.m%------X-------(Deceased)----+            |
  |           .m.PS13--..                                     |
  |      -- --#%######+m.                                     |
  |    .   -%m OLD #m- .         +----------------------+     |
  |  .---+%+*m DATA -.+          | Dockerized           |     |
  |..m---###%#*#m%%--..          | Postgres 13          |     |
  | -+%##*.--m--.----------------+----o-------.         |     |
  |.m +-.m-.+m.. .               |            |         |     |
  | +- .-*    ..                 +------------+---------+     |
  +---++--+-----------------------------------|---------------+
                                              |
                                              V
                                          Data is freed!