hyperhive/docs/2-handbook/swarm/matrix.md

# Swarm Matrix homeserver

Private Matrix homeserver (matrix-tuwunel — the conduwuit
successor) wrapped in a nixos-container (`hive-matrix`), plus optional fluffychat-web
client at `chat.<swarm-domain>/` (the `gatewayHost` vhost). A swarm runs one
homeserver, on one host. Two namespaces configure it:

- `services.hyperhive.swarm.matrix.*` — what the homeserver **is**, as
  every hive sees it: `serverName`, `gatewayHost`.
- `services.hyperhive.deploy.matrix.*` — what the host running it decides:
  `enable`, `gui.package`, `trustedServers`,
  `maxRequestSize`, `sso.clientSecretFile`.

Vhost routing lives in [`gateway.md`](../../4-implementation/networking/gateway.md).

## Container shape

Same shape as [`gateway.md::hive-forge container shape`](../../4-implementation/networking/gateway.md):

- Container name `hive-matrix` (not `h-*`) so c0re's lifecycle
  scanner ignores it; operator manages via the standard
  `nixos-container` CLI.
- Keeps hive-matrix from fighting any `services.matrix-*` the
  operator already runs on the host — separate systemd namespace,
  separate state dir.
- Container runs in a network namespace of its own
  (`privateNetwork = true`) on the hive bridge, and binds no TCP port. Agents
  reach the homeserver at `chat.<swarm-domain>` via the gateway, which
  dials its unix socket (see [Reach](#reach)).
- Persistent state at
  `/var/lib/nixos-containers/hive-matrix/var/lib/matrix-tuwunel/`
  survives container restart / host reboot. To wipe, destroy the
  container.

## Identity vs API listener: `serverName` vs `gatewayHost`

Two distinct hostnames:

- **`serverName`** — matrix-spec `server_name`, embedded
  *irrevocably* in every `@user:<server_name>` and `!room:<server_name>`
  identifier minted on this homeserver. You can't change it later
  without abandoning every account and chat history. Defaults to the
  bare `services.hyperhive.swarm.domain`.
- **`gatewayHost`** — the API listener hostname, where the gateway's
  matrix vhost proxies `/_matrix/*` to tuwunel. Defaults to
  `chat.<services.hyperhive.swarm.domain>`. Set to `null` to skip the
  gateway vhost, which leaves nothing able to reach the homeserver.

Both default under the **swarm** domain, because a swarm runs one
homeserver: tying its identity to a single hive's domain would make
relocating the container between hives look like a different
homeserver.

⚠️ **they're still not interchangeable, and the difference is the
cost of changing one.** `gatewayHost` is a routing detail clients
rediscover through `.well-known`, so it's safe to move on a running
deployment. The controller's host serves that `.well-known` on the swarm
domain, and a homeserver pinned to a hive domain gets it on that hive's
vhost. The matrix id format bakes `serverName` into every user and
room id, so adopting a new one does **not** rename the existing users and rooms —
it strands them, because their ids still name a homeserver that no
longer answers.

<details><summary>Pinning <code>serverName</code> on a homeserver with existing ids</summary>

`serverName` defaults to the bare `services.hyperhive.swarm.domain`. A
homeserver that changes `serverName` after minting ids strands its
existing users and rooms — keep the value it minted them under:

```nix
services.hyperhive.swarm.matrix = {
  # whichever this deployment already uses
  serverName = config.services.hyperhive.domain;
  gatewayHost = "matrix.${config.services.hyperhive.domain}";
};
```

A rebuild on a host that already has a homeserver prints a
`hive-matrix: WARNING — … serverName is unset` line when this is missing,
naming the value it's about to default to. It never fails the rebuild, so
pin the value before the homeserver mints any ids under the default.

A pinned hive domain answers `.well-known/matrix/*` itself, built from
`gatewayHost`, on any host that runs that hive's gateway. It doesn't need
the homeserver on the same host.

</details>

## Reach

tuwunel binds no TCP port. It listens on the unix socket
`/run/hive-matrix/tuwunel.sock`, in a host directory (`root:nginx`,
`0770`) bind-mounted into the container, and the gateway's
`/_matrix/` location proxies to that socket. Clients, agents, hive-c0re
and federation peers all reach the homeserver at `chat.<swarm-domain>`
through the gateway; from outside the host that takes
`gateway.openFirewall`.

hive-c0re doesn't talk to the homeserver: matrix is swarm-level, and
the hive has no matrix API URL to set.

Federation peers find the homeserver through `.well-known/matrix/server`
at the server name, which names `<gatewayHost>:443`
([`gateway.md::Discovery flow`](../../4-implementation/networking/gateway.md#discovery-flow-matrix)).
Port 8448 isn't used.

Outbound, the container sits on the hive bridge like the CI runner: it
leases an address from the gateway's DHCP, resolves through its dnsmasq,
and leaves through the bridge's NAT. It reaches the secret store,
authelia and federation peers by name.

## Provisioning flow (appservice)

<!-- vale write-good.Passive = NO -->
Registration is closed. **The swarm's appservice** creates accounts: agents
never see an appservice token, and an agent only ever receives its own
`access_token`.
<!-- vale write-good.Passive = YES -->

The appservice has no URL (`url: null` in its registration), so the
homeserver never calls out to it and there is no service to run. What the
registration buys is an identity the homeserver recognises — which is why
no secret has to be equal on both sides of the wire, and why account
creation doesn't depend on registration being open to anyone who learns
a token.

1. **`swarm-matrix-ctl appservice render`**, inside the `hive-matrix`
   container and before tuwunel starts, fetches the `as_token` and
   spec-required `hs_token` from the store and renders the registration to
   `/run/swarm-matrix-appservice/swarm.yaml` (mode `0600 root:root`) on the
   container's tmpfs, so no token sits on disk. It mints a pair only when
   the store answers and holds none. While the store doesn't answer, `render`
   fails and retries, and tuwunel stays down.
2. **systemd `LoadCredential=`** copies the registration into
   `/run/credentials/tuwunel.service/swarm-appservice.yaml`, owned by
   tuwunel's dynamic user with mode `0400`, at service start. The source
   file stays `root:root 0600` — no `chown :tuwunel` / `chmod 0640` /
   GID-pin gymnastics required. Keeps `DynamicUser = true` +
   `PrivateUsers = true` intact.
3. tuwunel's `appservice_dir` points at the credentials directory. It
   reads only `.yaml`/`.yml` entries from there, so the sibling
   credentials are invisible to it. The `.yaml` suffix on the credential
   id is what makes this work.
4. **hive-c0re** holds no appservice token, creates no account and does
   not talk to matrix.
5. **`swarm-controller` creates every account**: each agent's, with its
   token stored at `swarm/agents/<agent>/matrix/main` for the agent's
   `hive-matrix-daemon` to read as the agent itself, and each hive's
   sender account (below).

A homeserver whose `swarm-matrix-ctl` has no store identity
(`services.hyperhive.deploy.matrix.ctlBaoClientCertFile`) loads no
registration, and nothing creates accounts on it.

On the store's host `ctlBaoClientCertFile` / `ctlBaoClientKeyFile` default
to the leaf `glue-bao-tls.nix` mints there. A homeserver host without the
store gets no default, even when it holds the hive's own reader
`deploy.bao.clientCertFile`: issue a leaf whose subject is
`deploy.bao.matrixCtlCommonName`, place it, and name it in both options.
Until you do, `swarm-bao-matrix-oidc` fails naming both.

### The swarm's appservice, and its admin sender

The registration's id is `swarm`, its sender `@swarm`, and its user
namespace non-exclusive. It's the swarm's identity on the homeserver:
`swarm-controller` creates every agent's account and every hive's sender
account with it.

The swarm secret store holds the registration's tokens, at
`swarm/controller/swarm-controller/matrix/appservice-registration`.
`swarm-matrix-ctl appservice render` fetches them and renders the
registration tuwunel loads as a credential onto the `hive-matrix`
container's tmpfs, before tuwunel starts.
A render that can't reach the store fails and retries, and tuwunel, which fails to start without the registration, retries until one has landed.
`appservice sync` runs beside tuwunel on a timer. The store's tokens win:
when they differ from the rendered copy, it rewrites it. It
restarts tuwunel whenever the registration is newer than tuwunel's last
start, so the next run retries one that failed after writing, and starts
one that failed because `render` couldn't reach the store. A store that
holds none takes the tokens an earlier version kept in
`/var/lib/swarm-matrix-appservice` with a create-only write, so a running
swarm keeps its value; the files stay, unused. A host with neither files nor stored tokens mints a pair. `sync` then writes the `as_token`
to `swarm/controller/swarm-controller/matrix/appservice-token`. No hive's
policy reaches either path: only matrix-ctl (which holds `create` and
`read` on the registration, and writes the token) and `swarm-controller`
(which reads only the token) hold a grant.

`@swarm` is the **one** account the homeserver promotes to admin at boot
(`admin_execute`). Only those two principals read its token, which is
the difference from the hive sender below: every hive reads its own
sender's token. `swarm` is a reserved name, so nothing can create an agent
as this account.

`swarm-controller` mints each agent's account with the device id
`hyperhive-<agent>`, and a login on that device replaces its token. The controller therefore reads
the stored token back with `whoami` every five minutes and re-mints only
when it's missing, unknown to the homeserver, or someone else's. An
agent's daemon picks a re-minted token up on its next start, and a timer
restarts it while it's down.

### Operators are homeserver admins

Every member of authelia's `admins` group who has a matrix account is a
homeserver admin. `swarm-controller` reads the group through
`swarm-authelia-bridge` at start and every five minutes after, and for
each member not yet in `#admins:<server_name>` it sends
`!admin users make-user-admin @<name>:<server_name>` there as `@swarm`.
`<name>` is the authelia username lowercased, the account an SSO login
lands on.

- **Leaving `admins` revokes what the sync granted.** The controller
  records each account it sends a grant for in
  `/var/lib/swarm-controller/operator-matrix-admins.json`. When one of
  them is no longer in `admins` but still in `#admins`, it sends
  `!admin users force-leave-room @<name>:<server_name> <admin room id>`
  there as `@swarm`; leaving that room is what ends homeserver admin.
- **Admins the sync didn't make keep admin.** An admin missing from that
  file, `@swarm`, the server user `@conduit:<server_name>`, every agent's
  account, and every user id in
  `services.hyperhive.deploy.swarm-controller.matrixAdminSync.ignoreUsers` are never
  revoked.
- **The last admin stays.** A revoke that would leave no admin in
  `#admins` besides `@swarm` and the server user isn't sent; the
  controller logs a warning on each pass instead.
- **No account, no grant.** A member who has never logged in to matrix
  has no account to promote. The first pass after their first SSO login
  promotes them.
- **One command per account per controller run.** A member still missing
  from `#admins` after the controller sends its grant gets a
  `make-user-admin … failed to take` warning in the controller log on
  each later pass, and no second command until the controller restarts;
  a revoke that leaves its account in `#admins` gets
  `force-leave-room … failed to take` the same way.
- Runs only on a controller with both
  `services.hyperhive.deploy.swarm-controller.authBridgeUrl` and
  `services.hyperhive.deploy.swarm-controller.matrixHomeserverUrl` set.

### A hive's sender account, and why it isn't an admin

`@hive-<hive>:<server_name>` is the account a hive acts as.
`swarm-controller` creates it with the swarm's appservice token, for every
hive in its directory. It's an **ordinary account**: nothing promotes it;
the homeserver's `admin_execute` promotes only `@swarm`.

**One account per hive.** The localpart carries the hive's name, so a swarm
whose hives share a homeserver gives each of them its own identity: the
homeserver attributes an action to the hive that took it, and revoking one
hive's standing leaves the others alone.

Its access token is the **sender token**. `swarm-controller`, its only
minter, mints it for every hive with the swarm's appservice token and
publishes it to `swarm/hives/<hive>/matrix/sender-token`, inside the hive's own
read grant (`swarm/hives/<hive>/*`). Nothing on the hive uses it any more:
hive-c0re used to present it for its Space and invite calls and no longer
makes any. The name says what it authenticates as — an account the
swarm's appservice creates — rather than any privilege level, because it
carries none.

Promoting a user to homeserver admin and resetting a password both need an
admin **sender**: `!admin …` messages into `#admins:<server_name>`, and
tuwunel only treats a message as a command when its sender is already an
admin. Of the swarm's own accounts only `@swarm` is a homeserver admin
(operators are too, see
[Operators are homeserver admins](#operators-are-homeserver-admins)), so
both are swarm-level operations.

<details><summary>Appservice identity</summary>

`swarm-matrix-ctl appservice render` renders the registration from the
store's copy of the appservice tokens before tuwunel starts, so every
boot has both halves. With the store down or sealed, tuwunel waits for it.

<!-- vale write-good.Passive = NO -->
- **Access tokens live on the device that minted them.**
  `login_with_password` stays on, so the password fallback works
  too.
- **The homeserver's `admin_execute` promotes only `@swarm` at boot**
  (above); a hive's sender account is never promoted.
- **The value that matters lives at
  `swarm/controller/swarm-controller/matrix/appservice-token`.**
  `appservice sync` writes it there whenever the store's differs from the
  registration's `as_token`, and `swarm-controller` reads it from there.
<!-- vale write-good.Passive = YES -->

</details>

Initial rollout settings:

- `allow_federation = true` at the protocol level so swarms can be
  wired up later by extending `trustedServers` without a homeserver
  restart. `trusted_servers = []` keeps it effectively closed
  until you list peers.
- `allow_registration = false`. tuwunel checks this flag only for
  requests that arrive **without** an appservice token, so the swarm's
  appservice still creates accounts and tuwunel refuses everyone else. With no
  registration token configured, `allow_registration = true` makes
  tuwunel refuse to start unless
  `yes_i_am_very_very_sure_…_open_registration_…` is also set.
- `allow_encryption` — server-side E2EE switch, sourced from
  `services.hyperhive.deploy.matrix.allowEncryption` (**default `false`**, opt-in).
  Off by default because on the swarm's own homeserver the operator
  already controls the transport; turn it on for encrypted rooms on
  external / federated homeservers or to keep contents opaque to the
  homeserver admin. **The agent matrix client always supports decryption
  regardless of this flag** — it uses the `e2e-encryption` feature of
  `matrix-sdk` so it can read encrypted rooms it's invited to even when
  this homeserver doesn't permit room encryption. matrix-sdk stores
  crypto keys in the per-agent sqlite store under the state dir; they persist across
  restarts. `read_room` decrypts via
  `room.messages()` — UTD events surface as `event_type =
  "m.room.encrypted"` with `body = "[unable to decrypt]"`.
  The daemon bootstraps cross-signing on the bearer token alone, which
  works where the homeserver skips re-auth for a first key upload
  (MSC3967, as tuwunel does).
- **Key backup.** `swarm-controller` mints a random recovery passphrase
  for every matrix account an agent has, at
  `swarm/agents/<agent>/matrix-recovery/<account>` in the swarm secret
  store, and never replaces it. When `hive-matrix-daemon` brings an
  account up it reads that passphrase: with no backup on the account's
  homeserver it turns on server-side key backup and secret storage
  (log line `matrix recovery enabled`), unless the account already has
  secret storage, which it never replaces (a `WARN` instead). With a
  backup there it recovers from it (`recovered from the server-side key backup`), which downloads the
  room keys and signs the new device with the account's existing
  cross-signing identity. A crypto store lost to `--purge` or to a
  primary-token reset therefore comes back with its history. With no passphrase
  stored yet the account comes up without backup and picks it up on the
  next daemon start. A failure is a `WARN` and never stops the daemon.

The module's retired hive-side code, its evaluation assertions and the
fluffychat-web build fixes are in the
[implementation notes](../../4-implementation/networking/matrix-homeserver.md).

## Configuration tuning

```nix
services.hyperhive.deploy.matrix = {
  trustedServers  = [ "matrix.org" "example.com" ];   # default: []
  maxRequestSize  = 20000000;                          # default: 20 MB
};
```

**`trustedServers`** (default `[]`) — list of peer homeserver names
whose signing keys tuwunel fetches and trusts. tuwunel enables
federation at the protocol level from first boot (`allow_federation =
true`) but trusts no remote homeserver until you list it here. For a closed
single-hive deployment the default empty list is correct — add peer
hive domains here when connecting hives into a swarm (see
[`docs/2-handbook/swarm/`](README.md)).

**`maxRequestSize`** (default `20_000_000` bytes = 20 MB) — maximum
size of a single matrix client request body. Matches the matrix-spec
recommendation for media uploads and the upstream tuwunel default.
Raise for deployments that need large file transfers; lower for
resource-constrained hosts where a 20 MB request is unexpectedly large.