hyperhive/nix/host-modules/glue-queue-agent-credential.nix

# Glue: this hive's agent queue credential comes out of the secret store.
#
# The store's second reader, and deliberately the same shape as its first
# (./glue-matrix-bao-token.nix): a cert login that fails LOUDLY because every
# state it fails on is one a retry fixes, then a read that degrades QUIETLY
# because no retry turns "no value there" into a value.
#
# ⚠️ Two files, not one, and that is the consumer's shape rather than a
# preference. `swarm_queue_client::QueueConfig::from_env` takes the secret as
# a PATH (`<prefix>_OIDC_CLIENT_SECRET_FILE`) and the client id as a VALUE
# (`<prefix>_OIDC_CLIENT_ID`), so splitting them here is what lets the next
# slice hand both to an agent without parsing anything.
#
# ⚠️ An ABSENT file means this hive's agents do not connect to the queue, and
# that is correct rather than degraded. The publisher runs on the authelia
# host and authelia mints on its first boot, so "nothing at that path yet" is
# the ordinary early state of a swarm. Nothing here writes a local stand-in:
# unlike a matrix appservice token there is no such thing as a locally valid
# OIDC client secret, so a placeholder would turn a hive that cannot connect
# into one that is refused, which reaches the agent as a timeout.
#
# 📌 This runs wherever a client identity is configured, NOT only where the
# store is — the rule ./glue-matrix-bao-token.nix states in full. There is no
# "this hive runs agents" condition to gate it on as well: agent containers
# are created at runtime by hive-c0re, so every hyperhive host is a host that
# may run one.
{
  pkgs,
  lib,
  config,
  ...
}:
let
  hyperhiveCfg = config.services.hyperhive;
  deployCfg = hyperhiveCfg.deploy;
  baoCfg = hyperhiveCfg.swarm.bao;

  baoDeploy = deployCfg.bao;

  # What decides whether this unit exists at all. A reader is defined by holding
  # a certificate the store accepts, and that is true on the store's own host
  # and on a hive three networks away for exactly the same reason.
  #
  # 🩸 This principal's OWN leaf, not `clientCertFile` — the hive's, which four
  # units used to share. Bao matches a cert-auth role on the CN, so one leaf for
  # four readers was ONE principal holding the union of four grants: read on
  # `swarm/agents/*` AND `swarm/hives/<hive>/*` AND `swarm/services/*`, when
  # this unit reads one queue credential and nothing else. Its own leaf carries
  # `<queueAgentCommonNamePrefix>-<hive>` and its role grants the single path
  # below — still this hive's own, so the narrowing costs no reach.
  haveClientIdentity =
    baoDeploy.queueAgentClientCertFile != null && baoDeploy.queueAgentClientKeyFile != null;

  credentialDir = toString deployCfg.hive-controller.queue.agentCredentialDir;
  secretFile = "${credentialDir}/secret";
  clientIdFile = "${credentialDir}/client_id";

  # Where the credential lives in the store, spelled from the same pieces the
  # writer uses. Whoever writes it and whoever reads it must agree, and the
  # agreement belongs in one visible place.
  #
  # ⚠️ The `hives/<name>` segment is not decoration — it is what the reader's
  # own grant covers, so a path outside it is a 403 rather than a miss, however
  # correct it looks. `swarm-secret-client`'s `queue::agent_client_path` builds
  # the same string from the same pieces; this literal is the nix half of that
  # one agreement.
  #
  # `hiveName` has no fallback here for the reason ./glue-bao-tls.nix gives at
  # its own use of it: it is asserted set for every hyperhive host.
  credentialPath = "secret/swarm/hives/${hyperhiveCfg.hiveName}/queue/agent";
in
{
  options.services.hyperhive.deploy.hive-controller.queue = {
    agentCredentialDir = lib.mkOption {
      type = lib.types.path;
      default = "/var/lib/hyperhive/queue-agent";
      description = ''
        Host directory holding this hive's agent queue credential: `secret`
        (the OIDC client secret, `0600`) and `client_id` (the client that
        secret authenticates, `0644` — it is sent to the token endpoint on
        every connection and is not itself a secret).

        Both files are written by `swarm-bao-queue-agent.service`, which also
        creates this directory. Named here because nothing else creates it:
        the parent `/var/lib/hyperhive` belongs to `hive-c0re.service`'s
        `StateDirectory=`, which re-applies its own mode on every start, and a
        second declaration of *that* path is the two-mechanisms-one-path trap
        ./hive-gateway/default.nix records — so this directory is the unit's
        to make and the parent stays c0re's.

        Absent files mean this hive has no queue credential yet, which is what
        a swarm looks like before the publisher on the authelia host has run.
      '';
    };
  };

  config = lib.mkIf (hyperhiveCfg.enable && haveClientIdentity) {
    # Same rule as the unit's own gate: this reader exists on any host holding
    # a client identity, which is not every host that runs the store, so the
    # store's module cannot name it.
    services.hyperhive.swarm.otel.journaldUnits = [ "swarm-bao-queue-agent" ];

    systemd.services.swarm-bao-queue-agent = {
      description = "fetch this hive's agent queue credential from the swarm secret store";
      # Every one of these names a unit that exists only where the store runs.
      # `Requires=` on an absent unit fails the job outright, so the ordering is
      # conditional even though the read is not: off-host there is nothing local
      # to wait for, and the timeout below is what bounds the attempt instead.
      after = lib.optionals baoDeploy.enable [
        "swarm-bao-pki.service"
        "container@${baoCfg.machine}.service"
      ];
      wants = lib.optionals baoDeploy.enable [ "container@${baoCfg.machine}.service" ];
      requires = lib.optionals baoDeploy.enable [ "swarm-bao-pki.service" ];
      # Ordered before hive-c0re, so no agent container renders ahead of an
      # attempt at its credential. `Wants=`, not `Requires=`: a store this
      # unit can't reach delays hive-c0re's start by its own start-limit
      # window (`TimeoutStartSec`, retried up to `startLimitBurst` times
      # below) rather than failing it — hive-c0re starts once that window
      # elapses, whatever credential is or isn't on disk by then.
      before = [ "hive-c0re.service" ];
      wantedBy = [
        "multi-user.target"
        "hive-c0re.service"
      ];
      path = [
        baoDeploy.package
        pkgs.coreutils
      ];
      # Sized for the race this loses, not for an unseal: `swarm-bao` comes up
      # seconds before this unit asks, and the cert-auth role it logs in
      # against is written seconds after, so a few short attempts cover it.
      # An hours-long window would be a bet on a store that is sealed, and the
      # degrade below is already correct for that.
      #
      # `StartLimit*` are `[Unit]` settings, so they go here and not in
      # `serviceConfig` — systemd ignores them under `[Service]`. The window
      # has to exceed `RestartSec × burst`.
      startLimitBurst = 4;
      startLimitIntervalSec = 300;
      serviceConfig = {
        Type = "oneshot";
        RemainAfterExit = true;
        # What actually bounds the reads below. Stated here rather than left to
        # systemd's default, so the number a boot waits on is in the file that
        # waits.
        TimeoutStartSec = 30;
        Restart = "on-failure";
        RestartSec = 15;
      };
      environment = {
        BAO_ADDR = "https://${baoCfg.domain}:${toString baoCfg.port}";
        BAO_CLIENT_CERT = baoDeploy.queueAgentClientCertFile;
        BAO_CLIENT_KEY = baoDeploy.queueAgentClientKeyFile;
      }
      # Absent means the system trust store, which is what a deployment with a
      # real CA wants and what a self-signed one must not be left with.
      // lib.optionalAttrs (baoDeploy.serverCaFile != null) {
        BAO_CACERT = baoDeploy.serverCaFile;
      };
      script = ''
        set -euo pipefail

        # `bao`'s own message is the only thing separating a missing value from
        # a refused identity from an unreachable host. This unit's degraded
        # mode is correct for all three, so it reports which one rather than
        # asserting all three in a sentence of ours.
        err="$(mktemp)"
        trap 'rm -f "$err"' EXIT

        # Cert auth is a login, not a transport setting. The `BAO_CLIENT_*`
        # variables above only decide which certificate the TLS handshake
        # presents; without a token `bao` asks its token helper instead, and
        # that is a `sh` this unit's `path` does not carry. `-token-only`
        # answers on stdout and skips the helper on both sides.
        #
        # Fails LOUDLY, unlike the reads below: the three states a login
        # failure covers — store not up, sealed, role not written yet — are all
        # things a retry fixes, and `Restart=on-failure` above is what retries.
        if ! BAO_TOKEN="$(bao login -method=cert -token-only 2>"$err")"; then
          echo "could not log in to swarm-bao with this host's certificate; leaving the queue credential in ${credentialDir} as it is." >&2
          if [ -s "$err" ]; then
            cat "$err" >&2
          else
            echo "bao failed without writing a diagnostic." >&2
          fi
          exit 1
        fi
        export BAO_TOKEN

        # Two reads of one object rather than one `-format=json` parsed with
        # `jq`: no sibling unit carries `jq` on its `path`, and the pair cannot
        # actually disagree — the client id is derived from this hive's name, so
        # a rotation landing between these two calls changes the secret and
        # rewrites the same id.
        if ! secret="$(bao kv get -field=value ${lib.escapeShellArg credentialPath} 2>"$err")"; then
          echo "swarm-bao did not return ${credentialPath}; this hive's agents have no queue credential yet." >&2
          if [ -s "$err" ]; then
            cat "$err" >&2
          else
            echo "bao failed without writing a diagnostic." >&2
          fi
          exit 0
        fi

        if ! client_id="$(bao kv get -field=client_id ${lib.escapeShellArg credentialPath} 2>"$err")"; then
          echo "${credentialPath} holds no client_id; the secret alone is not a usable credential, so nothing is written." >&2
          if [ -s "$err" ]; then
            cat "$err" >&2
          else
            echo "bao failed without writing a diagnostic." >&2
          fi
          exit 0
        fi

        # Both or neither, for the reason `QueueConfig::from_env` refuses a
        # half-set environment: a client that finds one of the two comes up
        # "fine" and never connects.
        if [ -z "$secret" ] || [ -z "$client_id" ]; then
          echo "swarm-bao returned an empty field of ${credentialPath}; leaving the files as they are." >&2
          exit 0
        fi

        install -d -m 0755 ${lib.escapeShellArg credentialDir}

        umask 077
        printf '%s\n' "$secret" > ${lib.escapeShellArg secretFile}
        chmod 0600 ${lib.escapeShellArg secretFile}

        # `0644` on purpose: an OIDC client id is presented to the token
        # endpoint on every connection and is public by construction.
        printf '%s\n' "$client_id" > ${lib.escapeShellArg clientIdFile}
        chmod 0644 ${lib.escapeShellArg clientIdFile}
      '';
    };
  };
}