fips/testing/sidecar/README.md

# FIPS Sidecar

Run FIPS as a network sidecar container, providing mesh-only network
access to a companion application. The app container shares the FIPS
container's network namespace and is isolated from the host network by
iptables rules — it can only communicate over the FIPS mesh via `fips0`.

This is the recommended deployment pattern when connecting to an untrusted
public FIPS mesh: the application never touches the underlying transport
network, so it cannot leak traffic outside the mesh or be reached by
non-mesh peers.

## Quick Start

```bash
cd testing/sidecar
./scripts/build.sh
docker compose up -d

# Verify the sidecar is running:
docker exec fips-sidecar fipsctl show status

# Verify the app container can see the FIPS interface:
docker exec fips-app ip addr show fips0
```

With the default `.env`, FIPS starts with no peers. See
[Run with peers](#run-with-peers) to connect to an existing mesh.

## Security Model

The sidecar pattern enforces strict network isolation on the app container:

- **No IPv4 access**: iptables blocks all eth0 traffic except FIPS UDP
  transport (port 2121). The app container cannot reach the Docker bridge,
  the host network, or any IPv4 address.
- **No IPv6 on eth0**: ip6tables blocks all IPv6 traffic on eth0. The app
  container cannot use link-local or any Docker-assigned IPv6 addresses.
- **FIPS mesh only**: The only routable network path is through `fips0`
  (`fd::/8`). All application traffic traverses the FIPS mesh with
  end-to-end encryption.
- **Loopback allowed**: `lo` is unrestricted for inter-process communication
  within the shared namespace.

This means the app container treats the FIPS mesh as its sole network. Even
if the application is compromised, it cannot bypass the mesh or communicate
with the transport layer directly.

## Architecture

```text
┌───────────────────────────────────────────────────┐
│ Shared network namespace                          │
│                                                   │
│ ┌───────────────┐    ┌──────────────────────────┐ │
│ │ fips-sidecar  │    │ fips-app                 │ │
│ │               │    │                          │ │
│ │ fips daemon   │    │ your workload            │ │
│ │ fipsctl       │    │                          │ │
│ │ dnsmasq       │    │                          │ │
│ └───────────────┘    └──────────────────────────┘ │
│                                                   │
│ Interfaces:                                       │
│   lo    — loopback (unrestricted)                 │
│   eth0  — Docker bridge (iptables: FIPS only)     │
│   fips0 — FIPS TUN (fd::/8, unrestricted)         │
└───────────────────────────────────────────────────┘
```

The FIPS sidecar owns the network namespace and creates the `fips0` TUN
interface. The app container joins via `network_mode: service:fips` and
sees the same interfaces. The entrypoint script applies iptables rules
before launching the FIPS daemon:

**IPv4 rules** (iptables):

- ACCEPT on `lo` (both directions)
- ACCEPT UDP sport/dport 2121 on `eth0` (FIPS transport)
- DROP everything else on `eth0`

**IPv6 rules** (ip6tables):

- ACCEPT on `lo` (both directions)
- ACCEPT on `fips0` (both directions)
- DROP everything on `eth0`

### DNS Resolution

DNS inside the container is handled by dnsmasq (127.0.0.1:53):

- `.fips` queries are forwarded to the FIPS daemon's built-in DNS resolver
  (127.0.0.1:5354), which resolves npub-based names to `fd::/8` addresses
- All other queries are forwarded to Docker's embedded DNS (127.0.0.11)

The `resolv.conf` mount points the container's resolver at 127.0.0.1,
where dnsmasq handles the routing.

## Build

```bash
cd testing/sidecar
./scripts/build.sh
```

This compiles FIPS for Linux, copies the binaries into the Docker context,
and builds the sidecar and app images. Cross-compilation from macOS is
supported via `cargo-zigbuild`.

## Run with Peers

To connect the sidecar to an existing mesh, provide the peer's npub and
transport address:

```bash
FIPS_PEER_NPUB=npub1... \
FIPS_PEER_ADDR=203.0.113.10:2121 \
FIPS_PEER_ALIAS=gateway \
docker compose up -d
```

Verify the peer link:

```bash
docker exec fips-sidecar fipsctl show peers
docker exec fips-sidecar fipsctl show links
```

## Verify Connectivity and Isolation

From the app container:

```bash
# Ping a mesh node by npub (resolves via .fips DNS):
docker exec fips-app ping6 -c3 npub1sjlh2c3x9w7kjsqg2ay080n2lff2uvt325vpan33ke34rn8l5jcqawh57m.fips

# Fetch a web page from a mesh node over FIPS:
docker exec fips-app curl -6 "http://[fd69:e08d:65cc:3a6b:9c2c:2ac4:bd40:5e4b]:8000/"

# Docker bridge is blocked — this should fail:
docker exec fips-app ping -c1 -W2 172.20.0.13

# Loopback is allowed:
docker exec fips-app ping -c1 127.0.0.1
```

## Environment Variables

| Variable | Default | Description |
|---|---|---|
| `FIPS_NSEC` | *(required)* | Node secret key (hex or nsec1 bech32) |
| `FIPS_PEER_NPUB` | *(empty)* | Peer's npub to connect to |
| `FIPS_PEER_ADDR` | *(empty)* | Peer's transport address (e.g. `203.0.113.10:2121`) |
| `FIPS_PEER_ALIAS` | `peer` | Human-readable peer name |
| `FIPS_UDP_BIND` | `0.0.0.0:2121` | UDP transport bind address |
| `FIPS_TUN_MTU` | `1280` | TUN interface MTU |
| `FIPS_NETWORK` | `fips-sidecar-net` | Docker network name (set to join external network) |
| `FIPS_SUBNET` | `172.20.1.0/24` | Docker network subnet |
| `FIPS_IPV4` | `172.20.1.20` | Sidecar's IPv4 address on the Docker network |
| `RUST_LOG` | `info` | FIPS log level |

## Troubleshooting

**`FIPS_NSEC is required`** — The `FIPS_NSEC` environment variable is not
set. Either add it to `.env` or pass it on the command line. Generate a
random key with: `openssl rand -hex 32`

**`fips0` interface not appearing** — The FIPS daemon needs `/dev/net/tun`
and `NET_ADMIN` capability. Check that the compose file includes both:

```yaml
cap_add:
  - NET_ADMIN
devices:
  - /dev/net/tun:/dev/net/tun
```

**No peer connection established** — Verify the peer address is reachable
from the sidecar container (`docker exec fips-sidecar ping -c1 <peer-ip>`).
If joining an external Docker network, ensure `FIPS_NETWORK`, `FIPS_SUBNET`,
and `FIPS_IPV4` match the target network. Check logs with
`docker logs fips-sidecar`.

**DNS not resolving `.fips` names** — Verify dnsmasq is running:
`docker exec fips-sidecar pgrep dnsmasq`. Check that `resolv.conf` is
mounted (should contain `nameserver 127.0.0.1`). Verify the FIPS DNS
resolver is listening: `docker exec fips-sidecar dig @127.0.0.1 -p 5354 <npub>.fips AAAA`.

**iptables errors in entrypoint** — The sidecar container requires
`NET_ADMIN` capability for iptables. Without it, the isolation rules
cannot be applied and the entrypoint will fail.

## Production Considerations

**Secrets management**: The default `.env` contains a hardcoded nsec for
development. In production, use Docker secrets, a vault, or inject the key
via a secure CI/CD pipeline. Never commit production keys to version control.

**Logging**: Set `RUST_LOG` to control log verbosity (`debug`, `info`,
`warn`, `error`). For production, configure the Docker logging driver with
size limits:

```yaml
logging:
  driver: json-file
  options:
    max-size: "10m"
    max-file: "3"
```

**Resource limits**: Add memory and CPU constraints in the compose file:

```yaml
deploy:
  resources:
    limits:
      memory: 256M
      cpus: "0.5"
```

**Multiple peers**: The entrypoint supports a single peer via environment
variables. For multiple peers, mount a custom `fips.yaml` directly:

```yaml
volumes:
  - ./my-fips.yaml:/etc/fips/fips.yaml:ro
```

**Health checks**: Add a Docker health check using `fipsctl`:

```yaml
healthcheck:
  test: ["CMD", "fipsctl", "show", "status"]
  interval: 30s
  timeout: 5s
  retries: 3
```