Use harmonia instead of attic for binary cache

nixos/boxes/colony/vms/shill/containers/object.nix

@@ -31,6 +31,13 @@ in
     {
       config = mkMerge [
         {
+          fileSystems = {
+            "/var/lib/harmonia" = {
+              device = "/mnt/atticd/harmonia";
+              options = [ "bind" ];
+            };
+          };
+
           my = {
             deploy.enable = false;
             server.enable = true;
@@ -48,6 +55,7 @@ in
                   group = config.my.user.config.group;
                 };
                 "object/atticd.env" = {};
+                "nix-cache.key" = {};
                 "object/hedgedoc.env" = {};
                 "object/wastebin.env" = {};
               };
@@ -68,14 +76,26 @@ in
             };
           };
 
-          users = with lib.my.c.ids; let inherit (config.services.atticd) user group; in {
-            users."${user}" = {
-              isSystemUser = true;
-              uid = uids.atticd;
-              group = group;
-            };
-            groups."${user}".gid = gids.atticd;
-          };
+          users = with lib.my.c.ids; mkMerge [
+            (let inherit (config.services.atticd) user group; in {
+              users."${user}" = {
+                isSystemUser = true;
+                uid = uids.atticd;
+                group = group;
+              };
+              groups."${user}".gid = gids.atticd;
+            })
+            {
+              users = {
+                harmonia = {
+                  shell = pkgs.bashInteractive;
+                  openssh.authorizedKeys.keyFiles = [
+                    lib.my.c.sshKeyFiles.harmonia
+                  ];
+                };
+              };
+            }
+          ];
 
           systemd = {
             network.networks."80-container-host0" = networkdAssignment "host0" assignments.internal;
@@ -93,7 +113,9 @@ in
                   MINIO_BROWSER_REDIRECT_URL = "https://minio.nul.ie";
                 };
               };
+
               sharry = awaitPostgres;
+
               atticd = mkMerge [
                 awaitPostgres
                 {
@@ -104,6 +126,15 @@ in
                   };
                 }
               ];
+              harmonia = {
+                environment.NIX_REMOTE = "/var/lib/harmonia";
+                preStart = ''
+                  ${config.nix.package}/bin/nix store ping
+                '';
+                serviceConfig = {
+                  StateDirectory = "harmonia";
+                };
+              };
             };
           };
 
@@ -203,6 +234,14 @@ in
               };
             };
 
+            harmonia = {
+              enable = true;
+              signKeyPath = config.age.secrets."nix-cache.key".path;
+              settings = {
+                priority = 30;
+              };
+            };
+
             hedgedoc = {
               enable = true;
               environmentFile = config.age.secrets."object/hedgedoc.env".path;