Set up hydra as a remote build machine.

nix/configuration/hosts/hydra/default.nix

@@ -18,10 +18,43 @@
   ];
 
   config = {
-    # Generate with `head -c4 /dev/urandom | od -A none -t x4`
-    networking.hostId = "6fbf418b";
+    networking =
+      let
+        interface = "enp0s2";
+      in
+      {
+        # Generate with `head -c4 /dev/urandom | od -A none -t x4`
+        hostId = "6fbf418b";
 
-    networking.hostName = "hydra"; # Define your hostname.
+        hostName = "hydra"; # Define your hostname.
+
+        interfaces = {
+          "${interface}" = {
+            ipv4.addresses = [
+              {
+                address = "10.215.1.219";
+                prefixLength = 24;
+              }
+            ];
+
+            ipv6.addresses = [
+              {
+                address = "2620:11f:7001:7:ffff:ffff:0ad7:01db";
+                prefixLength = 64;
+              }
+            ];
+          };
+        };
+        defaultGateway = "10.215.1.1";
+        defaultGateway6 = {
+          # address = "2620:11f:7001:7::1";
+          address = "2620:11f:7001:7:ffff:ffff:0ad7:0101";
+          inherit interface;
+        };
+
+        dhcpcd.enable = lib.mkForce false;
+        useDHCP = lib.mkForce false;
+      };
 
     time.timeZone = "America/New_York";
     i18n.defaultLocale = "en_US.UTF-8";
@@ -63,13 +96,42 @@
 
     environment.systemPackages = with pkgs; [
       htop
+      git # for building on hydra
+      tmux # for building on hydra
+      nix-output-monitor # for building on hydra
     ];
 
     # nix.sshServe.enable = true;
     # nix.sshServe.keys = [ "ssh-dss AAAAB3NzaC1k... bob@example.org" ];
 
+    # Override garbage collection to keep things longer
+    # Automatic garbage collection
+    nix.gc = lib.mkForce {
+      automatic = true;
+      persistent = true;
+      dates = "weekly";
+      # randomizedDelaySec = "14m";
+      options = "--delete-older-than 60d";
+    };
+
+    # The default limit of files is 1024 which is too low for some nix builds.
+    #
+    # Check with `ulimit -n`
+    security.pam.loginLimits = [
+      {
+        domain = "*";
+        item = "nofile";
+        type = "-";
+        value = "8192";
+      }
+    ];
+
+    # systemd.user.extraConfig = "DefaultLimitNOFILE=8192";
+    # systemd.services."user@11400".serviceConfig.LimitNOFILE = "8192";
+
     me.build_in_ram.enable = true;
     me.dont_use_substituters.enable = true;
+    me.hydra.enable = true;
     me.minimal_base.enable = true;
     me.nix_worker.enable = true;
   };