hyperhive/docs/network.md

# hive-network

Host-side bridge + per-agent DNS resolver — the foundation that
makes container netns isolation safe to land. Configured via
`services.hyperhive.network.*`; off by default during rollout.

## Why ship before netns isolation

If netns isolation lands first, agent containers lose
`/etc/resolv.conf` propagation from the host and DNS breaks until a
separate resolver is up. Inverting the sequence — bridge + dnsmasq
first, netns flip second — makes the flag day boring: the resolver
endpoint is already live, agents just discover it via veth instead
of shared netns.

## v1 vs v2

| feature | v1 (this PR) | v2 (after netns isolation) |
|---|---|---|
| bridge interface | created on host, no slave NICs | per-agent veth pairs attach |
| dnsmasq binding | bridge IP (reachable via host loopback in shared netns) | bridge IP (reachable via veth in private netns) |
| agent container netns | shared host | private |
| agent `/etc/resolv.conf` | unchanged (host DNS) | `nameserver <bridge-ip>` |
| `address` rules target | `<bridge-ip>` (works in both modes) | unchanged from v1 |

The `address` rules ship pointing at the bridge IP from v1 so the
DNS contract is fixed before any container actually depends on it
— minimises the things that flip on netns day.

## 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` works without any veth gymnastics today; when
agent containers flip to private netns the binding doesn't change
(it's still on the host's bridge interface).

## Configuration

```nix
{
  services.hyperhive = {
    enable = true;
    domain = "darkest.space";
    network.enable = true;            # opt in to bridge + DNS
    network.bridgeIp = "10.42.0.1";   # default
    network.upstreamDns = [            # default Cloudflare + Quad9
      "1.1.1.1"
      "9.9.9.9"
    ];
  };
}
```

Asserts `services.hyperhive.domain != null` (resolver needs a domain
to be authoritative for) + `services.hyperhive.gateway.enable =
true` (resolver lives in the gateway container).

## 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 gets forwarded to `upstreamDns`. 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 ]`
+ `allowedTCPPorts = [ 53 ]` opens the resolver on the bridge
interface only. Other interfaces stay closed. The hive resolver
isn't an external-facing service.

When `isolateContainers = true`, `allowedTCPPorts` is extended with
`[ 80 443 ]` so isolated agents can reach nginx (gateway container,
shared host netns) for the forge sub-domain, per-agent UI proxies,
and any other HTTP services.

## Container isolation

`services.hyperhive.network.isolateContainers` (default `false`) flips
agent containers from shared host netns to private netns. Set only after
`enable = true` is stable in production — an assertion blocks the reverse.

### What the nix side does when `isolateContainers = true`

| 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 reach nginx on the host (shared netns) |
| Forge URL | `HIVE_FORGE_URL` flips from `http://127.0.0.1:3000` to `http://forge.<domain>` — agents resolve via dnsmasq, nginx proxies to forgejo |
| 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, when set, passes
`PRIVATE_NETWORK=1`, `LOCAL_ADDRESS=<deterministic-ip>`,
`HOST_ADDRESS=<bridge-ip>`, and `HOST_BRIDGE=<bridgeName>` via
`lifecycle::set_nspawn_flags` when creating or updating containers. Each
agent gets a deterministic IP derived from its name so the address is
reproducible across destroy/recreate. This applies uniformly to all
containers including the manager — no special case.

`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 must be replaced with the
bridge dnsmasq (the gateway IP). 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 the container's `/etc` **only when isolated**, removing
  it otherwise — so one shared container toplevel behaves correctly in both
  netns modes.
- the `hyperhive-isolated-dns` oneshot (harness-base.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; it's
  an instant no-op in shared-netns mode (the marker is absent, so
  `ConditionPathExists` skips it).

**Why isolation is safe for the manager**: all hive-c0re communication goes
through unix domain sockets (`/run/hive/mcp.sock` for agent requests,
`/run/hive/priv.sock` for privileged ops, per-agent manager sockets).
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.

### Prerequisites before flipping on

- All agents must have `hyperhive.web.useUnixSocket = true`. Agents that
  still bind TCP on `0.0.0.0:<port>` will be reachable at their bridge IP
  from other agents on the same subnet — defeating the isolation goal. The
  gateway routes via unix sockets so gateway reach is unaffected.

### Migration behaviour

Containers are destroyed and re-created when the flag flips. Agent state
under `/agents/<name>/state/` is bind-mounted and survives; the container
rootfs is recreated cleanly from the nix store.

## Cross-references

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