updates: postgres upgrade, data migration process

README.md

@@ -3,6 +3,9 @@
 A home for configuring all of my homelab containers on a Debian Linux machine.
 This assumes a Debian Linux machine with Docker and Docker Compose installed.
 
+My particular setup is based on a [jailmaker](https://github.com/Jip-Hop/jailmaker) container
+running on top of TrueNAS SCALE, separating all the docker stuff from the appliance.
+
 # Notes
 
 ## IPv6
@@ -16,3 +19,29 @@ that uses the IP of this host as the gateway.
 This is a limitation of my current ISP, I only have a single /64 subnet for my lab network.
 I'd like to get a /56 or /48, perhaps using Hurricane Electric's tunnel broker.
 *Sigh* ISPs being stingy with the 2^48 prefixes they're afraid of running out of.
+
+## Upgrading Postgres
+Upgrading the postgres container for a given stack requires a dump and restore.
+
+After making a snapshot or backup of postgres data directory,
+in the compose directory for a given stack, run the following commands:
+```bash
+docker compose down
+docker compose up -d <db_service>
+docker compose exec -it <db_service> pg_dumpall -U <db_user> | tee /tmp/dump.sql
+docker compose down
+
+rm -r <postgres_data_dir>/*  # as root
+# Edit the docker-compose.yml file to use the new postgres image
+docker compose up -d <db_service>
+# For some reason, compose exec doesn't like the input redirection
+docker exec -i <db_container_name> psql -U <db_user> < /tmp/dump.sql
+docker compose up -d
+rm /tmp/dump.sql
+```
+
+Additionally, if upgrading from postgres <= 13, it is necessary to upgrade the
+password hashes. This can be done by running the following command:
+```bash
+docker compose exec -it <db_service> psql -U <db_user> -c "\password"
+```