Temporary PostgreSQL Database with Docker

Every now and then I need to restore an old database backup to grab some data out of. I use Postgres containers for every app I work on, so I don’t really want to go polluting those. Here’s how I start a postgres container, restore a DB into it, do what I need to do, then destroy it.

1. Start the container: docker run --rm -it -v `pwd`:/data postgres bash
   • --rm means remove the container when it stops (we exit bash)
   • -it means give me a interactive terminal (I need to type stuff and see output)
   • -v means mount the directory I’m currently in to /data - assuming the directory I’m in has a PG dump I want to use.
2. Now in the container, we need to set up the database engine. The postgres container has an entrypoint script that normally does this for us, but we’ve told Docker to run bash rather than this script.
   • Create the cluster: pg_createcluster 9.5 main (replace 9.5 with whatever version of Postgres you have used)
   • Start Postgres: service postgresql start
   • Create a user for ‘root’: su - postgres -c "createuser -s root"
3. Now we have a superuser Postgres user named “root”, we can do whatever we want, for example:
   • createdb my_database
   • cd /data
   • psql my_database < my_database_backup.sql
   • psql my_database
   • SELECT count(*) from widgets
4. When we’re done, we just need to exit bash. The container will stop and be removed by Docker.