hyperhive/nix/host-modules/swarm-nats-service.nix

# The swarm's message queue as every hive sees it: where it is reached and
# what it is registered as, identical on every host. What the host running it
# decides, and the container itself, are in ./swarm-nats.nix.
{
  lib,
  config,
  ...
}:
let
  swarmDomain = config.services.hyperhive.swarm.domain;
  # Total on a null swarm domain, for the reason ./swarm-bao-service.nix gives.
  domainBase = if swarmDomain == null then "invalid" else swarmDomain;
in
{
  options.services.hyperhive.swarm.nats = {
    # `enable` is `services.hyperhive.deploy.nats.enable` — see
    # ./deploy.nix. What the queue IS to every hive: its domain, ports
    # and client id.

    # ⚠️ Deliberately NO `package` option for the NATS server, anywhere —
    # not here and not under `deploy.nats` either, where every other
    # service's build lives. `services.nats` upstream does not expose
    # one; it resolves `pkgs.nats-server` itself, so an option would be
    # ignored or need an overlay to mean anything, and an option that does
    # not control what it names is worse than its absence. Pin the build
    # with `nixpkgs.overlays` if you need to. (`deploy.nats.authPackage`
    # is a different thing: the callout responder, which IS ours.)

    domain = lib.mkOption {
      type = lib.types.str;
      default = "nats.${domainBase}";
      defaultText = lib.literalExpression ''"nats.''${services.hyperhive.swarm.domain}"'';
      description = ''
        Name every client reaches the queue on, as
        `tls://<domain>:<port>`, and the only name its certificate carries.
        A **sibling** of the swarm's other service names, for the reason
        {option}`services.hyperhive.swarm.bao.domain` gives.

        The host running the queue answers it through `gateway.localNames`.
        Every other hive resolves it through the operator's upstream DNS,
        which is where a multi-host swarm needs a record for it.

        Not in {option}`services.hyperhive.swarm.serviceDomains`: that list
        is the names a gateway vhost fronts, and nginx fronts nothing here.
      '';
    };

    port = lib.mkOption {
      type = lib.types.port;
      default = 4222;
      description = ''
        TCP port the queue listens on. 4222 is upstream's default and
        sits outside hyperhive's claimed ranges (dashboard 7000, forge
        3000, matrix 8008, every agent in 8100..8999 via FNV-1a hash).

        Opened on the bridge interface, for agent containers, and on
        `wg-hive` when this host is on the mesh, for other hives. Never
        host-wide. TLS only: a client that does not speak it is refused.

        Unlike {option}`monitorPort` and {option}`metricsPort`, the
        address is not what bounds who may use this port: the queue's
        `auth_callout` refuses every client it cannot identify.
      '';
    };

    monitorPort = lib.mkOption {
      type = lib.types.port;
      default = 8222;
      description = ''
        Port NATS serves its **monitoring** endpoint on, bound to
        loopback.

        Not a metrics endpoint: the server has no Prometheus format of its
        own. This serves `/varz`, `/connz`, `/routez` as JSON, and the
        exporter below is what translates it — which is why enabling the
        exporter without this produces a process that starts cleanly and
        scrapes nothing.

        ⚠️ Loopback, and the exporter is the only intended reader. The
        endpoint is unauthenticated and `/connz` names every connected
        client, so the address it binds is the whole access control. Do
        not widen it, and do not put it behind a gateway vhost expecting
        that to add one.
      '';
    };

    metricsPort = lib.mkOption {
      type = lib.types.port;
      default = 7777;
      description = ''
        Port the Prometheus exporter serves NATS's metrics on, bound to
        loopback for the swarm collector to scrape.

        ⚠️ This and {option}`monitorPort` are two more claims on a port
        space every swarm container shares — they run in this container but
        `privateNetwork = false`, so a collision with any other hyperhive
        service is a runtime coin toss over which process gets the port,
        with nothing in any log saying so. Both defaults are upstream's
        own (`nats-server` 8222, `prometheus-nats-exporter` 7777) and
        neither is claimed elsewhere in this repo, checked when they were
        added.
      '';
    };

    clientId = lib.mkOption {
      type = lib.types.str;
      default = "swarm-nats";
      description = ''
        OAuth2 client id the queue's authentication path identifies
        itself with. The host running authelia registers it, whichever
        host runs the queue, and the queue's host reads its secret out of
        the swarm secret store.
      '';
    };

  };
}