hosts/thrall/default.nix

@@ -9,6 +9,7 @@ let
 in {
   imports = [ # Include the results of the hardware scan.
     ./hardware-configuration.nix
+    ../../modules/upgrade-pg-cluster.nix
   ];
 
   nix.package = pkgs.nixUnstable;

modules/upgrade-pg-cluster.nix

@@ -0,0 +1,32 @@
+{ config, pkgs, ... }:
+{
+  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.withPackages (pp: [
+        # pp.plv8
+      ]);
+    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 $NEWBIN \
+        "$@"
+    '')
+  ];
+}