modules/autoupdate: add update-from-hydra script

README.md

@@ -116,6 +116,17 @@ nix run .#list-upgradable
 
 Checks all hosts with a `nixosConfiguration` in `flake.nix`.
 
+## Update from [Hydra build](https://hydra.hq.c3d2.de/jobset/c3d2/nix-config#tabs-jobs)
+
+The fastest way to update a system, a manual alternative to setting
+`c3d2.autoUpdate = true;`
+
+Just run:
+
+```shell
+update-from-hydra
+```
+
 ## Creating a new Proxmox container
 
 Use the `nixprox.sh` script that should be copied to

modules/autoupdate.nix

@@ -11,13 +11,12 @@
     default = false;
   };
 
-  config = lib.mkIf config.c3d2.autoUpdate {
-    # the presence of this file signifies that the system is
+  config = {
+    # the presence of this .service file signifies that the system is
     # autoupdate-enabled. it is checked to prevent autoupdating back
     # to a system without autoupdate when deploying with autoupdate
     # for the first time.
-
-    systemd.services.autoupdate = {
+    systemd.services.autoupdate = lib.mkIf config.c3d2.autoUpdate {
       wantedBy = [ "multi-user.target" ];
       path = with pkgs; [ nixFlakes nettools curl jq ];
       serviceConfig = {
@@ -55,9 +54,36 @@
       startAt = "hourly";
     };
 
-    nix.gc = {
+    nix.gc = lib.mkIf config.c3d2.autoUpdate {
       automatic = true;
       randomizedDelaySec = "6h";
     };
+
+    environment.systemPackages = [ (
+      # Provide a manual updating script that fetches the latest
+      # updated+built system from Hydra
+      pkgs.writeScriptBin "update-from-hydra" ''
+        #! ${pkgs.runtimeShell} -e
+
+        OLD=$(readlink /run/current-system)
+        echo Current system: $(basename $OLD)
+        NEW=$(curl -sLH "Accept: application/json" https://hydra.hq.c3d2.de/job/c3d2/nix-config/x86_64-linux.$(hostname)/latest | ${pkgs.jq}/bin/jq -r .buildoutputs.out.path)
+        if [ -z "$NEW" ]; then
+          echo "Unable to obtain updated system"
+          exit 1
+        fi
+        echo New system: $(basename $NEW)
+
+        if [ "$OLD" != "$NEW" ]; then
+          echo "Fetching new system built by https://hydra.hq.c3d2.de/jobset/c3d2/nix-config"
+          # this should fetch the new system from the binary cache
+          nix copy --from https://nix-serve.hq.c3d2.de "$NEW"
+          echo "Switch to the new system..."
+          "$NEW/bin/switch-to-configuration" switch
+        else
+          echo "No update required"
+        fi
+      ''
+    ) ];
   };
 }