♻️ consolidate nix configs

nix/modules/postgresql/default.nix

@@ -0,0 +1,44 @@
+{ pkgs, config, ... }: {
+  services = {
+    postgresql = {
+      enable = true;
+      package = pkgs.postgresql_14;
+    };
+
+    postgresqlBackup = {
+      enable = true;
+    };
+  };
+
+  # Postgres upgrades: https://nixos.org/manual/nixos/stable/index.html#module-services-postgres-upgrading
+  environment.systemPackages = [
+    (
+      let
+        # XXX specify the postgresql package you'd like to upgrade to.
+        # Do not forget to list the extensions you need.
+        newPostgres = pkgs.postgresql_15;
+      in
+      pkgs.writeScriptBin "upgrade-pg-cluster" ''
+        set -eux
+        # XXX it's perhaps advisable to stop all services that depend on postgresql
+        systemctl stop postgresql
+
+        export NEWDATA="/var/lib/postgresql/${newPostgres.psqlSchema}"
+
+        export NEWBIN="${newPostgres}/bin"
+
+        export OLDDATA="${config.services.postgresql.dataDir}"
+        export OLDBIN="${config.services.postgresql.package}/bin"
+
+        install -d -m 0700 -o postgres -g postgres "$NEWDATA"
+        cd "$NEWDATA"
+        sudo -u postgres $NEWBIN/initdb -D "$NEWDATA"
+
+        sudo -u postgres $NEWBIN/pg_upgrade \
+          --old-datadir "$OLDDATA" --new-datadir "$NEWDATA" \
+          --old-bindir $OLDBIN --new-bindir $NEWBIN \
+          "$@"
+      ''
+    )
+  ];
+}