lxc: start an impl on server7

hosts/server7/containers/default.nix

@@ -35,4 +35,11 @@ let
 in {
   boot.enableContainers = true;
   inherit containers;
+
+  imports = [ ../../../lib/lxc ];
+  lxc.containers = {
+    trivial = {
+      nixos-config = "/tmp/trivial.nix";
+    };
+  };
 }

lib/lxc/default.nix

@@ -0,0 +1,62 @@
+{ config, lib, pkgs, ... }:
+with lib;
+
+let
+  profilesDir = "/nix/var/nix/profiles/lxc";
+  gcRoots = "/nix/var/nix/gcroots/lxc";
+  containers = config.lxc.containers;
+in {
+  options = with types; {
+    lxc.containers = mkOption {
+      type = attrs;
+      default = {};
+    };
+  };
+
+  config = mkIf (containers != {}) {
+    virtualisation.lxc = {
+      enable = true;
+    };
+
+    systemd.services =
+      builtins.foldl' (services: name:
+        let
+          config = builtins.getAttr name containers;
+          builder = {
+            description = "Build NixOS for lxc container ${name}";
+            wants = [ "nix-daemon.socket" ];
+            after = [ "nix-daemon.service" ];
+
+            path = with pkgs; [ coreutils nix ];
+
+            serviceConfig.Type = "oneshot";
+            serviceConfig.RemainAfterExit = true;
+
+            script = ''
+              mkdir -p ${profilesDir}/${name}
+              mkdir -p ${gcRoots}/${name}
+
+              nix-env -p ${profilesDir}/${name}/system \
+                -I nixos-config=${config.nixos-config} \
+                -f '<nixpkgs/nixos>' \
+                --set -A system
+            '';
+          };
+          starter = {
+            description = "LXC container ${name}";
+            requires = [ "lxc-container-${name}-builder" ];
+            after = [ "lxc-container-${name}-builder" ];
+
+            path = with pkgs; [ lxc ];
+
+            script = ''
+              lxc-start -F -n ${name}
+            '';
+          };
+        in services // {
+          "lxc-container-${name}-builder" = builder;
+          "lxc-container-${name}" = starter;
+        }
+      ) {} (builtins.attrNames containers);
+  };
+}