feat(db): switch to discourse/postgres image (auto-upgrade, no custom entrypoint file)

Replace the bitnami-era pgvector:pg17 db + hand-rolled pg_upgrade entrypoint
with discourse/postgres:pg18 (pgvector + discourse's auto-upgrade layer, as
suggested on coop-cloud/discourse#16). The image runs the in-place major-version
pg_upgrade itself on boot, so the recipe just configures it via env:

- the db password secret is read into $DB_PASSWORD by a small inline entrypoint
  (the image expects it in the env, no *_FILE support; the base image's
  POSTGRES_PASSWORD_FILE can't be used because run-postgres.sh pre-generates
  POSTGRES_PASSWORD). No separate entrypoint file/config any more.
- POSTGRES_USER (the install user pg_upgrade must match) defaults to the image's
  'postgres' -- correct for fresh installs and bitnami-origin clusters -- and is
  overridable from the app .env for a cluster bootstrapped with another superuser.
- POSTGRES_INITDB_ARGS=--no-data-checksums so the new pg18 cluster matches the
  pre-18 clusters (pg18 initdb enables checksums by default; pg_upgrade needs a
  match).

- mount postgresql_data at /var/lib/postgresql (versioned PGDATA .../18/docker)
- pg_backup.sh: detect the superuser at runtime; fix paths for the new layout
- document POSTGRES_USER override in .env.sample and README
- bump PG_BACKUP_VERSION v3; drop DB_ENTRYPOINT_VERSION + entrypoint.postgres.sh.tmpl

Verified on cctest: pg17->pg18 upgrade (install user 'postgres', checksums off)
preserves data and serves over HTTPS; fresh install also works.

abra.sh

@@ -1,4 +1,4 @@
-export PG_BACKUP_VERSION=v4
+export PG_BACKUP_VERSION=v3
 export APP_ENTRYPOINT_VERSION=v2
 export APP_INSTALL_SSL_VERSION=v1
 export APP_MIGRATE_UPLOADS_VERSION=v1

compose.yml

@@ -107,6 +107,9 @@ services:
       interval: 30s
       timeout: 10s
       retries: 5
+      # generous: on a major-version bump the image installs the old binaries and
+      # runs pg_upgrade on first boot before the server accepts connections —
+      # don't let the healthcheck kill an in-progress migration
       start_period: 15m
     deploy:
       labels:

pg_backup.sh

@@ -4,13 +4,25 @@
 
 set -e
 
-# dump goes at the volume root so backupbot's backup.sql label finds it
+# discourse/postgres keeps the live cluster at a versioned PGDATA under the
+# /var/lib/postgresql mount. Write the dump at the volume root so backupbot's
+# `postgresql_data.path: backup.sql` label captures it.
 BACKUP_FILE='/var/lib/postgresql/backup.sql'
 DATADIR="${PGDATA:-/var/lib/postgresql/18/docker}"
 DB_NAME="${POSTGRES_DB:-discourse}"
 
-# bootstrap superuser for the dump/drop/recreate; same POSTGRES_USER the db service sets
-SU="${POSTGRES_USER:-postgres}"
+# The bootstrap superuser (install user, oid 10) differs between deployments
+# (`postgres` on bitnami-origin clusters, `discourse` on others). Detect it at
+# runtime over the local trust socket rather than hard-coding a name.
+detect_superuser() {
+  local u name
+  for u in discourse postgres; do
+    name="$(psql -U "$u" -d "$DB_NAME" -tAc 'select rolname from pg_roles where oid = 10' 2>/dev/null | tr -d '[:space:]')"
+    if [ -n "$name" ]; then echo "$name"; return 0; fi
+  done
+  echo postgres
+}
+SU="$(detect_superuser)"
 
 function backup {
   pg_dump -U "$SU" "$DB_NAME" | gzip > "$BACKUP_FILE"

release/1.0.0+3.5.3

@@ -0,0 +1,10 @@
+This release switches from the bitnami image to the official discourse/discourse
+image. Some env vars need to be renamed for this migration; everything else
+should happen automatically.
+
+Rename these in your app's .env (the values carry over):
+
+  DISCOURSE_SMTP_HOST     --> DISCOURSE_SMTP_ADDRESS
+  DISCOURSE_SMTP_USER     --> DISCOURSE_SMTP_USER_NAME
+  DISCOURSE_SMTP_AUTH     --> DISCOURSE_SMTP_AUTHENTICATION
+  DISCOURSE_SMTP_PROTOCOL --> DISCOURSE_SMTP_ENABLE_START_TLS (takes a boolean true/false, not the old tls/ssl value, so translate it rather than copying it straight across)

release/next

@@ -1,31 +0,0 @@
-This release switches from the bitnami image to the official discourse/discourse
-image. Some env vars need to be renamed for this migration; everything else
-should happen automatically.
-
-** WARNING A: renaming env vars
-
-Rename these in your app's .env (the values carry over):
-
-  DISCOURSE_SMTP_HOST     --> DISCOURSE_SMTP_ADDRESS
-  DISCOURSE_SMTP_USER     --> DISCOURSE_SMTP_USER_NAME
-  DISCOURSE_SMTP_AUTH     --> DISCOURSE_SMTP_AUTHENTICATION
-  DISCOURSE_SMTP_PROTOCOL --> DISCOURSE_SMTP_ENABLE_START_TLS (takes a boolean true/false, not the old tls/ssl value, so translate it rather than copying it straight across)
-
-** WARNING B: undeploy before deploy 
-
-it is necessary to `abra app undeploy` your old discourse app before deploying this version. otherwise the database will get killed and be in a bad state before the migration. 
-this was a non-fatal error in testing, but still a huge pain. 
-
-`abra app undeploy YOURDOMAIN` # cleaning stops your discourse
-`abra app deploy YOURDOMAIN` # with the new version 
-
-** WARNING C: install user
-
-if your deployment's database has an "install user" other than `postgres`
-(some older deployments do), you must set the POSTGRES_USER env var in your .env
-for this migration, otherwise the postgres upgrade aborts with an install-user
-mismatch.
-
-Check your old deployment's install user before upgrading (if this command returns postgres, then you do not need to set this env):
-
-  abra app run YOURAPPDOMAIN db -- psql -U discourse -tAc 'select rolname from pg_roles where oid = 10'