hyperhive/nix/modules/hive-network.nix

{
  lib,
  config,
  ...
}:
let
  cfg = config.services.hyperhive.network;
in
{
  # Hive-internal network — host-side bridge + per-agent DNS resolver.
  # Containers stay on shared host netns at v1; this module stands the
  # bridge + resolver up so the endpoint is in place before network
  # isolation flips containers to private netns. Full design: docs/network.md.

  options.services.hyperhive.network = {
    enable = lib.mkOption {
      type = lib.types.bool;
      default = false;
      example = true;
      description = ''
        Stand up the hive-internal bridge + dnsmasq resolver.
        Off by default while v1 phases in. When enabled:
        a bridge interface (`bridgeName`) appears on the host with
        `bridgeIp` assigned, and the hive-gateway container runs a
        dnsmasq listening on that IP for `<hive-domain>` +
        sub-domains. Agent containers still default to shared host
        netns at v1 — the endpoint is up but only used once #14
        lands and flips containers to a private netns + veth peer
        on this bridge.
      '';
    };

    bridgeName = lib.mkOption {
      type = lib.types.str;
      default = "hive-br0";
      example = "h0";
      description = ''
        Name of the host-side bridge interface the hive uses for
        inter-container traffic. Kept short so it survives the
        IFNAMSIZ (15-char) cap, and prefixed so it's obviously
        hive-managed in `ip link` output.
      '';
    };

    bridgeIp = lib.mkOption {
      type = lib.types.str;
      default = "10.42.0.1";
      example = "172.30.0.1";
      description = ''
        IPv4 address assigned to the bridge interface on the host
        side. Becomes the DNS server address agents point at (and
        the upstream the gateway proxies to once netns isolation
        lands). Default `10.42.0.1` is in RFC 1918 space and
        unlikely to clash with operator's existing setup; override
        if a different range is already in use.
      '';
    };

    bridgePrefixLength = lib.mkOption {
      type = lib.types.int;
      default = 24;
      example = 16;
      description = ''
        Netmask prefix length for the bridge subnet. Default `/24`
        gives 254 usable per-agent addresses, enough for any
        single-host hive. Operator with a larger swarm or a tighter
        addressing scheme overrides.
      '';
    };

    upstreamDns = lib.mkOption {
      type = lib.types.listOf lib.types.str;
      default = [
        "1.1.1.1"
        "9.9.9.9"
      ];
      example = [
        "192.168.1.1"
        "8.8.8.8"
      ];
      description = ''
        Upstream DNS servers dnsmasq forwards non-hive queries to.
        Defaults to Cloudflare + Quad9. Override for operators on
        private networks who need a specific resolver (corporate
        DNS, pi-hole, etc.). The hive resolver itself stays
        authoritative for `<hive-domain>` and its sub-domains
        regardless of upstream choice.
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    assertions = [
      {
        assertion = config.services.hyperhive.domain != null;
        message = ''
          services.hyperhive.network.enable = true requires
          services.hyperhive.domain to be set — the resolver needs a
          domain to be authoritative for. Either pin a hostname
          (`services.hyperhive.domain = "example.com";`) or leave
          `network.enable` at its default of false.
        '';
      }
      {
        assertion = config.services.hyperhive.gateway.enable;
        message = ''
          services.hyperhive.network.enable = true requires
          services.hyperhive.gateway.enable = true — the dnsmasq
          resolver runs inside the hive-gateway container (single
          front-door for both DNS and HTTP). Enable the gateway or
          leave `network.enable` at its default of false.
        '';
      }
    ];

    # Bridge interface on the host. Empty interfaces list = purely
    # virtual bridge (no slave NICs attached). Per-agent veth pairs
    # will join this bridge once #14 lands; at v1 it stands alone.
    networking.bridges.${cfg.bridgeName}.interfaces = [ ];

    # Host-side IP assignment on the bridge. This is what dnsmasq
    # (inside the gateway container, shared host netns) binds on.
    networking.interfaces.${cfg.bridgeName}.ipv4.addresses = [
      {
        address = cfg.bridgeIp;
        prefixLength = cfg.bridgePrefixLength;
      }
    ];

    # Open the resolver port in the host firewall for traffic from
    # the bridge subnet only. Other interfaces stay closed —
    # external DNS-amplification surface is not exposed.
    networking.firewall.interfaces.${cfg.bridgeName} = {
      allowedUDPPorts = [ 53 ];
      allowedTCPPorts = [ 53 ];
    };
  };
}