docs(dev): exporting pgdata

SETUP.md

@@ -2,7 +2,7 @@
 
 You have two options when setting up a development environment for Ion: Docker or Vagrant. Docker is probably going to work better, so try it first.
 
-**The Git repository on the host computer is synced with ``~/intranet`` on the virtual machine, so you can edit files within the repo on the host computer with a text editor of your choice and the changes will be immediately reflected on the virtual machine.**
+The Git repository on the host computer is synced with ``~/intranet`` on the virtual machine, so you can edit files within the repo on the host computer with a text editor of your choice and the changes will be immediately reflected on the virtual machine.
 
 # Docker
 
@@ -29,6 +29,10 @@ Navigate to http://localhost:8080 in the web browser of your choice. You might h
 
 If you need to run a Django command like ``makemigrations``, ``collectstatic`` or ``shell_plus``, run ``docker exec -it application bash`` in your terminal. That wlll give you a shell into the application container. You can also use this to run scripts like ``build_sources.sh``. If you need to view the output from or restart ``runserver``, run ``docker attach application``.
 
+### Attaching to logs
+
+To view logs of a container, run `docker logs [CONTAINER NAME] -f`. For example, to view the logs of the web server, run `docker logs intranet -f`.
+
 # Vagrant
 
 ## Prerequisites
@@ -138,3 +142,42 @@ You can find a list of file systems at ``intranet/apps/files/models.py``. To add
     $ ./manage.py shell_plus
     >>> Host.objects.create(name="Computer Systems Lab", code="csl", address="remote.tjhsst.edu", linux=True)
 
+# Advanced
+
+## Backup or export database from Docker
+
+Use these instructions to create a backup of your development environment's postgres database and, if desired, import it into another container or Docker instance running on a different machine.
+
+### Overview
+
+For the Ion development environment, database information is stored in [Docker volumes](https://docs.docker.com/storage/volumes/), under the name `docker_pgdata`. On a linux environment, volumes are stored in `/var/lib/docker/volumes`.
+
+### Creating a backup volume
+
+To create a backup of your volume on your local device, make a copy of `/var/lib/docker/volumes/docker_pgdata` to a location you will remember.
+
+### Mount to another container
+
+To create another database container with the postgres data mounted, run:
+
+``docker run -it -v docker_pgdata:/var/lib/postgresql/data postgres:latest /bin/bash``
+
+### Export to another machine or Docker instance
+
+Follow these steps to export your data if you are creating a new development environment on a different machine. These steps assume you already have a running dev environment on the target machine.
+
+Warning: you are likely to see errors that you will have to Google and solve yourself. Only do this if you have a substantial amount of data you need for your new environment; otherwise, it's easier to simply create another environment and add the data manually.
+
+1. Create a copy of your data in case something goes wrong (see creating a backup volume section).
+2. On the new machine, copy the postgres volume to your volume directory. Do this either through an USB, other file transfer method, or SSH. If using `scp`, run:
+   ``scp -r  [USERNAME]@[HOST]:/var/lib/docker/volumes/docker_pgdata /var/lib/docker/volumes/``
+
+Because you have copied over old configuration files to a new machine, the new postgres instance may think certain files are corrupted and not start. To correct this, do the following:
+
+3. Create a container with the volume mounted:
+   ``docker run -it -v /docker_pgdata:/var/lib/postgresql/data postgres:latest /bin/bash``
+4. Run `apt update && apt install sudo`
+5. Run `sudo -u postgres pg_resetwal /var/lib/postgresql/data`
+6. Run `dd if=/dev/zero bs=1 count=8192 >> data/pg_xact/0000`
+7. Exit the postgres container and restart your development environment. It should now contain all the data you had in your volume.
+8. If something doesn't work, Google it...(and if you're feeling nice, add it here).