nixos-servers/nix/virtual/default.nix

{ pkgs, lib, config, hypervisorConfig, ... }: {
  imports = [ ./docker_swarm.nix ];

  options.lab.vm = {
    # TODO: make global.
    baseMACAddress = lib.mkOption {
      default = "BA:DB:EE:F0:00:00";
      type = lib.types.str;
      description = ''
        Base MAC address for VMs in the DMZ.
      '';
    };

    id = lib.mkOption {
      type = lib.types.int;
      description = ''
        Unique identifier of this VM from wich the MAC address is derived.
      '';
    };

    shares = lib.mkOption {
      default = [ ];
      description = ''
        Directories mounted on the VM using VirtioFS.
      '';
      type = lib.types.listOf (lib.types.submodule ({ config, ... }: {
        options = {
          name = lib.mkOption {
            type = lib.types.str;
            description = ''
              The name of the directory share.
            '';
          };

          mountPoint = lib.mkOption {
            type = lib.types.str;
            description = ''
              The mount point of the directory share inside the virtual machine.
            '';
          };
        };
      }));
    };
  };

  config = {
    system.stateVersion = hypervisorConfig.system.stateVersion;

    lab.vm.shares = [{
      name = "host_keys";
      mountPoint = "/etc/ssh/host_keys";
    }];

    services.openssh =
      let
        hostKeyPath = "/etc/ssh/host_keys/ssh_host_ed25519_key";
      in
      {
        hostKeys = [{
          path = hostKeyPath;
          type = "ed25519";
        }];

        extraConfig = ''
          HostKey ${hostKeyPath}
        '';
      };

    microvm = {
      # TODO: make this dependent on the host CPU
      vcpu = 4;

      shares = [{
        source = "/nix/store";
        mountPoint = "/nix/.ro-store";
        tag = "ro-store";
        proto = "virtiofs";
      }] ++ map
        (share: {
          source = "/var/lib/microvms/${config.networking.hostName}/shares/${share.name}";
          mountPoint = share.mountPoint;
          tag = share.name;
          proto = "virtiofs";
        })
        config.lab.vm.shares;

      interfaces = [{
        type = "tap";
        id = "vm-${config.networking.hostName}";
        mac = pkgs.lib.net.mac.add config.lab.vm.id config.lab.vm.baseMACAddress;
      }];
    };
  };
}