hyperhive/docs/network.md

# hive-network

Host-side bridge + per-agent private-netns isolation — always on
whenever hyperhive is enabled. Configured via
`services.hyperhive.network.*`.

> Isolation is the only mode — there is no shared-netns fallback. The
> former `services.hyperhive.network.enable`,
> `services.hyperhive.network.isolateContainers` and
> `services.hyperhive.network.upstreamDns` options were removed; a
> config that still sets one fails eval with a removal message.

## Container shape (where dnsmasq lives)

Co-located in the existing `hive-gateway` container — single
front-door for both DNS and HTTP, saves a sibling container, single
systemd-unit / state surface to monitor. The gateway shares host
netns (`privateNetwork = false`) so dnsmasq's `bind-interfaces`
listener on `bridgeIp` is on the host's bridge interface.

## Configuration

```nix
{
  services.hyperhive = {
    enable = true;
    domain = "darkest.space";
    # network.bridgeIp = "10.42.0.1";   # default
  };
}
```

Requires `services.hyperhive.domain` to be set — the dnsmasq resolver
is authoritative for `<hive-domain>` and its sub-domains.

## Bridge addressing

Default subnet is `10.42.0.0/24`, host-side gateway at `10.42.0.1`.
RFC 1918 space, unlikely to clash with operator's existing setup;
override `bridgeIp` + `bridgePrefixLength` if a different range is
already in use. `/24` gives 254 usable per-agent addresses — enough
for any single-host hive; bigger swarms or tighter addressing
schemes pick their own.

## Resolver behaviour

dnsmasq is **authoritative** for the hive's own zones — answers
`<hive-domain>`, `forge.<hive-domain>`, `matrix.<hive-domain>`
queries with the bridge IP (where nginx is reachable). Everything
else is forwarded to the host's own resolvers: dnsmasq reads the
gateway container's `/etc/resolv.conf`, the host copy nixos-container
makes at each container start — a host resolver change is picked up
on the next gateway restart. Containers don't need to know the
upstream — they query the bridge IP and dnsmasq does the right thing
per-name.

`bind-interfaces` + `interface = [ bridgeName "lo" ]` means the
listener only accepts queries from the bridge interface (plus lo for
container health-checks). External hosts can't reach it — no
DNS-amplification surface even when the operator opens port 80 for
gateway HTTP.

`resolveLocalQueries = false` keeps dnsmasq out of the host's own
resolution stack — the host's resolver (systemd-resolved, plain
glibc nss, dnscrypt-proxy, etc.) keeps doing whatever the operator
configured. The hive resolver is purely for inbound queries from
agent containers.

## Firewall posture

`networking.firewall.interfaces.<bridge>.allowedUDPPorts = [ 53 67 ]`
`networking.firewall.interfaces.<bridge>.allowedTCPPorts = [ 53 80 443 ]`

- Port 53 opens the resolver on the bridge interface only. Other
  interfaces stay closed. The hive resolver isn't an external-facing
  service.
- Port 67 (UDP) admits DHCP requests to the dnsmasq pool. dnsmasq
  receives DHCP via a regular UDP socket (it does not use a
  netfilter-bypassing raw socket), so the hole is mandatory — without
  it containers never get a lease and fall back to 169.254.x.x.
- Ports 80 and 443 let isolated agents reach nginx (gateway
  container, shared host netns) for the forge sub-domain, per-agent
  UI proxies, and any other HTTP services.

### Reaching host services (`exposeHostPorts`)

By default agents can only reach the host on 80/443 (+53 DNS), so a
host-side service on another port — e.g. a dev OTEL collector for
`services.hyperhive.otel.endpoint` (see `docs/observability.md`) — is unreachable.

`services.hyperhive.network.exposeHostPorts = [ 4318 ];` opens each
listed TCP port `P` on the bridge-interface `allowedTCPPorts`, so an
agent can connect to `<bridgeIp>:P` (point the collector endpoint at
`http://<bridgeIp>:4318`, default `http://10.42.0.1:4318`).

This is **firewall-only**: the host service must bind an address
reachable from the bridge — `0.0.0.0` or the bridge IP — not loopback
only. The bridge→`127.0.0.0/8` DROP rule (below) is unchanged, so a
service bound to `127.0.0.1` only stays unreachable; rebind it to
`0.0.0.0`. (An earlier revision shipped a per-port
`systemd-socket-proxyd` bridge→loopback forwarder, but that collides
EADDRINUSE with any collector already bound to `0.0.0.0` — which is the
common case — so the proxy was dropped in favour of opening the port.)

The port is reachable by **every** agent on the bridge subnet (like
DNS/gateway), so only expose services safe for any agent to reach.

## Container isolation

Each agent container runs in a private network namespace with a dedicated
veth pair attached to the bridge. The following table summarises what
the nix side sets up unconditionally:

| effect         | mechanism                                                                                                                             |
| -------------- | ------------------------------------------------------------------------------------------------------------------------------------- |
| IP forwarding  | `boot.kernel.sysctl."net.ipv4.ip_forward" = 1`                                                                                        |
| Internet NAT   | `networking.nat { enable = true; internalInterfaces = [ bridgeName ]; }` — MASQUERADE on packets leaving via any external NIC         |
| Loopback DROP  | `networking.firewall.extraInputRules` — drops bridge-subnet → `127.0.0.0/8` traffic; defence-in-depth against routing table leaks     |
| Gateway access | `networking.firewall.interfaces.<bridge>.allowedTCPPorts = [ 80 443 ]` — lets isolated agents (private netns, veth on bridge) reach nginx on the host  |
| c0re signal    | `HIVE_NETWORK_ISOLATION=1`, `HIVE_NETWORK_BRIDGE`, `HIVE_NETWORK_SUBNET` in `systemd.services.hive-c0re.environment`                  |

`HIVE_NETWORK_SUBNET` is the host-side bridge IP + prefix (e.g.
`10.42.0.1/24`), **not** the canonical network address. The Rust side
must normalise (bitwise-AND with mask) before subnet membership checks or
address arithmetic.

### What the Rust side does

`hive-c0re` reads `HIVE_NETWORK_ISOLATION` and passes
`PRIVATE_NETWORK=1`, `LOCAL_ADDRESS=` (empty), `HOST_ADDRESS=<bridge-ip>`,
and `HOST_BRIDGE=<bridgeName>` via `lifecycle::set_nspawn_flags` when
creating or updating containers. `LOCAL_ADDRESS` is left empty so the
container's dhcpcd acquires an address from the bridge dnsmasq pool
(`networking.useDHCP = true` in `nix/agent-modules/network.nix`). This applies uniformly
to all containers — agents and service containers alike.

`HOST_ADDRESS` is the bridge gateway IP (the address part of
`HIVE_NETWORK_SUBNET`, via `lifecycle::bridge_gateway_ip` — taken verbatim
so a non-`.1` operator override still resolves to wherever the bridge
actually lives). It is **load-bearing**: nixos-container's container-side
network setup only installs a default route (`ip route add default via
$HOST_ADDRESS`) when `HOST_ADDRESS` is non-empty. In bridge mode the
host-side address/route setup is skipped, so writing it only affects the
container's default route — without it the container comes up with an IP
but no path off the bridge subnet (no internet, no `api.anthropic.com`).

### How the isolated container gets its resolver

nixos-container copies the **host's** `/etc/resolv.conf` into the container
at every start. The host resolver (e.g. `127.0.0.53` from systemd-resolved,
or a LAN router) is unreachable from a private netns and isn't
authoritative for the hive's own zones, so it is replaced with the
bridge dnsmasq at boot. Because the copy happens on every start, a
declarative `environment.etc."resolv.conf"` would be clobbered — so the
wiring is runtime:

- `hive-priv` drops a marker file (`/etc/hyperhive-bridge-dns`, carrying the
  gateway IP) into each container's `/etc`.
- the `hyperhive-isolated-dns` oneshot (`nix/agent-modules/network.nix`), gated on that
  marker, rewrites `/etc/resolv.conf` to `nameserver <gateway-ip>` at boot.
  It is ordered `before` the harness (`hive-ag3nt`), the matrix daemon, and
  `tea-login` so the resolver is correct before the first DNS lookup.

**Why isolation is safe**: all hive-c0re communication goes
through unix domain sockets (`/run/hive/mcp.sock` for agent requests,
`/run/hive/priv.sock` for privileged ops).
These are bind-mounted into containers via the nspawn conf. UDS paths
traverse the VFS, not the network stack, so `PRIVATE_NETWORK=1` does not
affect them.

The nix side also enables IP forwarding + NAT (agents reach the internet
through the host) and drops bridge-subnet → loopback traffic (defence-in-depth
against a compromised agent reaching the c0re dashboard HTTP at
`127.0.0.1`). Agents have no legitimate reason to reach the dashboard over
loopback — the hive-c0re admin socket is a UDS, not TCP.

## Cross-references

- `docs/gateway.md` — vhost map + the gateway container's other duties