hyperhive/nix/host-modules/lib/hive-ca-trust.nix

# Shared hive-CA trust plumbing for containers that must trust the
# self-signed gateway/forge leaf for *outbound* TLS (webhook delivery,
# CI artifact upload, …). The hive CA is generated at runtime by the host
# `hive-tls-ca.service` (see `hive-tls.nix`) — it can't be baked into a
# derivation — so each such container binds the public `ca.pem` read-only
# and orders its `container@<name>` unit after `hive-tls-ca.service` so the
# bind source exists before nspawn sets the mount up.
#
# `bindMount` + `containerOrdering` are the language-agnostic half. The
# *consumption* differs per runtime: an additive variable (Node's
# `NODE_EXTRA_CA_CERTS`, hive-ci) points straight at `caContainerPath` from
# the call site, while a *replacing* one (Go's `SSL_CERT_FILE`, rustls) needs
# the system-CAs+hive-CA concat that `trustBundle` below does for it.
#
# Pure function — NOT a NixOS module (don't add it to the host-modules
# aggregator). Call it from a module's `let`:
#
#   caTrust = import ./lib/hive-ca-trust.nix { inherit lib tlsCfg gatewayCfg; };
#   # then, in the container:
#   #   bindMounts = { … } // caTrust.bindMount;
#   #   systemd.services."container@hive-ci" = lib.mkMerge [ caTrust.containerOrdering … ];
#   #   environment.NODE_EXTRA_CA_CERTS = caTrust.caContainerPath;  # consumption, per-caller
#
# `tlsCfg`     = config.services.hyperhive.tls
# `gatewayCfg` = config.services.hyperhive.gateway
{
  lib,
  tlsCfg,
  gatewayCfg,
}:
let
  # `gateway.useSelfSigned` is the single source of truth for the
  # self-signed condition — no duplicated derivation.
  useSelfSigned = gatewayCfg.useSelfSigned;
  # The bundle, not `ca.pem`: the hive CA is an intermediate under the
  # swarm root, and openssl (which is what both consumers below sit on —
  # Node's `NODE_EXTRA_CA_CERTS`, Go's `SSL_CERT_FILE`) will not end a
  # chain at a trusted cert that isn't self-signed. `hive-tls.nix` writes
  # the bundle next to the CA and explains the split.
  caHostPath = "${tlsCfg.stateDir}/trust-bundle.pem";
  caContainerPath = "/run/hive-ca/trust-bundle.pem";
in
{
  inherit useSelfSigned caContainerPath;

  # Fold into the container's `bindMounts` via `//`. Binds ONLY the public
  # CA cert (never the `hive-tls` state dir — it holds the CA + leaf private
  # keys), read-only. Empty when not self-signed, so the whole trust path
  # drops out cleanly.
  bindMount = lib.optionalAttrs useSelfSigned {
    ${caContainerPath} = {
      hostPath = caHostPath;
      isReadOnly = true;
    };
  };

  # Fold into the caller's `container@<name>` unit (via `lib.mkMerge` if the
  # caller adds its own keys, e.g. hive-ci's `TimeoutStartSec`). Orders the
  # container after the host `hive-tls-ca.service` so the bind source exists
  # before nspawn sets the mount up — a condition-skipped/late CA would
  # otherwise fail the container start.
  containerOrdering = lib.mkIf useSelfSigned {
    after = [ "hive-tls-ca.service" ];
    requires = [ "hive-tls-ca.service" ];
  };

  # System CAs + hive CA in one bundle, with `SSL_CERT_FILE` set on each
  # consumer — for runtimes whose trust variable *replaces* the store (Go,
  # rustls-native-certs). An additive one (Node's `NODE_EXTRA_CA_CERTS`,
  # hive-ci) needs no bundle and should not use this.
  #
  #   imports = [ (caTrust.trustBundle { inherit pkgs; name = "swarm-nats";
  #                                      consumers = [ "swarm-nats-auth" ]; }) ];
  #
  # Three constraints, each earned:
  #   - `requires` on the CONSUMER: `before` orders but does not gate, so a
  #     failed assembly otherwise leaves it running and trusting *nothing*.
  #   - assemble to a temp path, verify, then move: `cat` of an empty bind
  #     exits 0, and a partial bundle must never appear under the final name.
  #   - `consumers` are BARE unit names — they are `systemd.services` keys
  #     (no suffix) *and* go in `before`/`requires` (suffixed). Reversed, the
  #     edge names a unit that does not exist and systemd orders nothing.
  #
  # Returns a module, not bare services: a caller already writing
  # `systemd.services.<consumer>` cannot also write `systemd.services`.
  #
  # The two host-consumer flags are documented at their use sites below.
  trustBundle =
    {
      name,
      consumers,
      pkgs,
      # A HOST systemd service rather than something inside a container.
      # `caContainerPath` is a bind mount that only exists in a container, so
      # a host consumer reads the host copy — which means waiting for the
      # unit that writes it. In a container that wait is the container's own
      # (`containerOrdering`); here nothing carries it. One flag, because a
      # host source without the ordering is a race.
      hostUnit ? false,
      # Whether the consumer exists at all. A container caller imports this
      # into the CONTAINER's module set, so it vanishes with the container. A
      # host caller imports it at the host's top level, where `imports` is
      # unconditional — without this, a hive with the consumer off still gets
      # a bundle oneshot *and* a `systemd.services.<consumer>` conjured by
      # `genAttrs`, holding an `SSL_CERT_FILE` and no `ExecStart`.
      enable ? true,
    }:
    let
      dir = "/run/${name}-ca";
      bundlePath = "${dir}/trust-bundle.pem";
      unit = "${name}-ca-bundle";
      source = if hostUnit then caHostPath else caContainerPath;
    in
    {
      _file = "hive-ca-trust.nix#trustBundle:${name}";
      config.systemd.services = lib.optionalAttrs (useSelfSigned && enable) (
        {
          ${unit} = {
            description = "assemble ${name} TLS trust bundle (system CAs + hive CA)";
            wantedBy = [ "multi-user.target" ];
            before = map (c: "${c}.service") consumers;
            # Only for a host consumer: the CA file is written at runtime by
            # `hive-tls-ca.service`, and reading it directly means waiting
            # for it. A container consumer reads a bind mount instead, and
            # its `container@` unit carries the equivalent wait.
            after = lib.optionals hostUnit [ "hive-tls-ca.service" ];
            requires = lib.optionals hostUnit [ "hive-tls-ca.service" ];
            serviceConfig = {
              Type = "oneshot";
              RemainAfterExit = true;
              SyslogIdentifier = unit;
            };
            path = [
              pkgs.coreutils
              pkgs.gnugrep
            ];
            script = ''
              set -euo pipefail
              install -d -m 0755 ${dir}
              tmp=${bundlePath}.tmp
              cat /etc/ssl/certs/ca-certificates.crt ${source} > "$tmp"
              # `cat` of an empty or missing-but-mounted source exits 0, so the
              # result has to be inspected rather than the command trusted.
              if ! grep -q 'BEGIN CERTIFICATE' "$tmp"; then
                echo "${unit}: assembled bundle contains no certificate" >&2
                exit 1
              fi
              chmod 0644 "$tmp"
              mv "$tmp" ${bundlePath}
            '';
          };
        }
        // lib.genAttrs consumers (_: {
          requires = [ "${unit}.service" ];
          after = [ "${unit}.service" ];
          environment.SSL_CERT_FILE = bundlePath;
        })
      );
    };
}