Reloadable containers

nixos/modules/system/activation/switch-to-configuration.pl

@@ -147,11 +147,16 @@ sub fingerprintUnit {
 while (my ($unit, $state) = each %{$activePrev}) {
     my $baseUnit = $unit;
 
-    # Recognise template instances.
-    $baseUnit = "$1\@.$2" if $unit =~ /^(.*)@[^\.]*\.(.*)$/;
     my $prevUnitFile = "/etc/systemd/system/$baseUnit";
     my $newUnitFile = "$out/etc/systemd/system/$baseUnit";
 
+    # Detect template instances.
+    if (!-e $prevUnitFile && !-e $newUnitFile && $unit =~ /^(.*)@[^\.]*\.(.*)$/) {
+      $baseUnit = "$1\@.$2";
+      $prevUnitFile = "/etc/systemd/system/$baseUnit";
+      $newUnitFile = "$out/etc/systemd/system/$baseUnit";
+    }
+
     my $baseName = $baseUnit;
     $baseName =~ s/\.[a-z]*$//;
 

nixos/tests/containers-reloadable.nix

@@ -0,0 +1,66 @@
+import ./make-test.nix ({ pkgs, lib, ...} :
+let
+  client_base = rec {
+
+    containers.test1 = {
+      autoStart = true;
+      config = {
+        environment.etc."check".text = "client_base";
+      };
+    };
+
+    # prevent make-test.nix to change IP
+    networking.interfaces = {
+      eth1.ip4 = lib.mkOverride 0 [ ];
+    };
+  };
+in {
+  name = "cotnainers-reloadable";
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ danbst ];
+  };
+
+  nodes = {
+    client = { lib, pkgs, ... }: {
+      imports = [ client_base ];
+    };
+
+    client_c1 = { lib, pkgs, ... }: {
+      imports = [ client_base ];
+
+      containers.test1.config = {
+        environment.etc."check".text = lib.mkForce "client_c1";
+        services.httpd.enable = true;
+        services.httpd.adminAddr = "nixos@example.com";
+      };
+    };
+    client_c2 = { lib, pkgs, ... }: {
+      imports = [ client_base ];
+
+      containers.test1.config = {
+        environment.etc."check".text = lib.mkForce "client_c2";
+        services.nginx.enable = true;
+      };
+    };
+  };
+
+  testScript = {nodes, ...}: let
+    originalSystem = nodes.client.config.system.build.toplevel;
+    c1System = nodes.client_c1.config.system.build.toplevel;
+    c2System = nodes.client_c2.config.system.build.toplevel;
+  in ''
+    $client->start();
+    $client->waitForUnit("default.target");
+    $client->succeed("[[ \$(nixos-container run test1 cat /etc/check) == client_base ]] >&2");
+
+    $client->succeed("${c1System}/bin/switch-to-configuration test >&2");
+    $client->succeed("[[ \$(nixos-container run test1 cat /etc/check) == client_c1 ]] >&2");
+    $client->succeed("systemctl status httpd -M test1 >&2");
+
+    $client->succeed("${c2System}/bin/switch-to-configuration test >&2");
+    $client->succeed("[[ \$(nixos-container run test1 cat /etc/check) == client_c2 ]] >&2");
+    $client->fail("systemctl status httpd -M test1 >&2");
+    $client->succeed("systemctl status nginx -M test1 >&2");
+  '';
+
+})