populate ip address based on hostname and populate the hostfile with other vm ips

nixos/machines/ghatanothoa/configuration.nix

@@ -14,6 +14,5 @@
 
   # System configuration here
   networking.hostName = "ghatanothoa";
-  vmNetwork.ipv4 = "192.168.0.25";
   system.stateVersion = "23.11";
 }

nixos/machines/lobon/configuration.nix

@@ -16,7 +16,6 @@
   };
 
   networking.hostName = "lobon";
-  vmNetwork.ipv4 = "192.168.0.22";
   system.stateVersion = "23.11";
 
   sops.secrets = {

nixos/machines/nodens/configuration.nix

@@ -11,6 +11,5 @@
   environment.systemPackages = [pkgs.git];
 
   networking.hostName = "nodens";
-  vmNetwork.ipv4 = "192.168.0.18";
   system.stateVersion = "24.11";
 }

nixos/machines/nyarlathotep/configuration.nix

@@ -40,7 +40,6 @@
   };
 
   networking.hostName = "nyarlathotep";
-  vmNetwork.ipv4 = "192.168.0.17";
   system.stateVersion = "24.05";
 
   sops.secrets = let

nixos/roles/hostmap.nix

@@ -0,0 +1,23 @@
+{
+  "192.168.1.11" = ["bragi"];
+  "192.168.0.13" = ["tsathoggua"];
+  "192.168.0.14" = ["nyogtha"];
+  "192.168.0.15" = ["hastur"];
+  "192.168.0.16" = ["cthulhu"];
+  "192.168.0.17" = ["nyarlathotep"];
+  "192.168.0.18" = ["nodens"];
+  "192.168.0.19" = ["uvhash"];
+  "192.168.0.20" = ["aphoom-zhah"];
+  "192.168.0.21" = ["dagon"];
+  "192.168.0.22" = ["lobon"];
+  "192.168.0.23" = ["yibb-tstll"];
+  "192.168.0.24" = ["eihort"];
+  "192.168.0.25" = ["ghatanothoa"];
+  "192.168.0.26" = ["toth"];
+  "192.168.0.27" = ["ithaqua"];
+  "192.168.0.28" = ["nyarlathotep"];
+  "192.168.0.29" = ["nixos-installer"];
+  "192.168.0.30" = ["cthugha"];
+  "192.168.0.40" = ["nerf-nixos-testlab"];
+  "192.168.0.92" = ["sanctamariamaterdei"];
+}

nixos/roles/vm.nix

@@ -1,5 +1,6 @@
 {modulesPath, ...}: {
   imports = [
     (modulesPath + "/virtualisation/xen-domU.nix")
+    ./vmNetwork.nix
   ];
 }

nixos/roles/vmNetwork.nix

@@ -0,0 +1,30 @@
+# This module assumes that every hostName of a machine in this repo only appears in one of the ip addresses,
+# to derive the ip adress based on the hostname this will need patching if we will ever have a vm with multiple
+# outward facing network interfaces.
+# (other hostnames can appear multiple times)
+{
+  lib,
+  config,
+  ...
+}: let
+  inherit (lib) lists;
+  inherit (builtins) elem;
+  # taken from aza /etc/hosts
+  hostmap = import ./hostmap.nix;
+  myhostName = config.networking.hostName;
+  # We replace our own ip with 127.0.0.1 in /etc/hosts
+  myhosts = lib.attrsets.concatMapAttrs (ip: hosts:
+    if (elem myhostName hosts)
+    # nixos maps the hostname to the loopback 127.0.0.2 by default, so we exclude it here.
+    # there is also a default localhost to 127.0.0.1 in place
+    then {"127.0.0.1" = lists.filter (x: x != myhostName) hosts;}
+    else {${ip} = hosts;})
+  hostmap;
+  myIp = (lists.findSingle (x: elem myhostName x.value) (throw "The machine has no ip address in nixos/roles/hostmap.nix") (throw "The ip for this machine is not unique in nixos/roles/hostmap.nix") (lib.attrsToList hostmap)).name;
+in {
+  imports = [
+    ../modules/vmNetwork.nix
+  ];
+  networking.hosts = myhosts;
+  vmNetwork.ipv4 = myIp;
+}