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

nixos/roles/hostmap.nix

@@ -1,21 +1,54 @@
+# This data is taken from /etc/hosts from azatoth
 {
-  "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"];
-  "192.168.0.30" = ["cthugha"];
-  "192.168.0.92" = ["sanctamariamaterdei"];
+  bragi = {
+    ipv4 = "192.168.1.11";
+  };
+  tsathoggua = {
+    ipv4 = "192.168.0.13";
+  };
+  nyogtha = {
+    ipv4 = "192.168.0.14";
+  };
+  hastur = {
+    ipv4 = "192.168.0.15";
+  };
+  cthulhu = {
+    ipv4 = "192.168.0.16";
+  };
+  nyarlathotep = {
+    ipv4 = "192.168.0.17";
+  };
+  nodens = {
+    ipv4 = "192.168.0.18";
+  };
+  uvhash = {
+    ipv4 = "192.168.0.19";
+  };
+  aphoom-zhah = {
+    ipv4 = "192.168.0.20";
+  };
+  dagon = {
+    ipv4 = "192.168.0.21";
+  };
+  lobon = {
+    ipv4 = "192.168.0.22";
+  };
+  yibb-tstll = {
+    ipv4 = "192.168.0.23";
+  };
+  eihort = {
+    ipv4 = "192.168.0.24";
+  };
+  ghatanothoa = {
+    ipv4 = "192.168.0.25";
+  };
+  toth = {
+    ipv4 = "192.168.0.26";
+  };
+  ithaqua = {
+    ipv4 = "192.168.0.27";
+  };
+  cthugha = {
+    ipv4 = "192.168.0.30";
+  };
 }

nixos/roles/vmNetwork.nix

@@ -1,26 +1,28 @@
-# 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 (lib) lists mapAttrsToList;
+  inherit (lib.attrsets) foldAttrs concatMapAttrs;
+  inherit (lib.asserts) assertMsg;
   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:
+  # To turn the hostmap around suitable for networking.hosts the following simple code almost works
+  # concatMapAttrs (hostname: ipData: { ${ipData.ipv4} = [hostname]; }) hostmap
+  # but breaks as soon as we want to map two different names to the same ip.
+  # So the code looks uglier than one would expect.
+  globalhosts = foldAttrs (a: b: a ++ b) [] (mapAttrsToList (hostname: ipData: {${ipData.ipv4} = [hostname];}) hostmap);
+  myhosts = 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;
+  globalhosts;
+  myIp = assert assertMsg hostmap ? ${myhostName}.ipv4 "${myhostName} has no ip configured in nixos/roles/hostmap.nix"; hostmap.${myhostName}.ipv4;
 in {
   imports = [
     ../modules/vmNetwork.nix