fips/testing/sidecar

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

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 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

┌───────────────────────────────────────────────────┐
│ 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

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:

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

Verify the peer link:

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

Verify Connectivity and Isolation

From the app container:

# 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:

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:

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

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

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:

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

Health checks: Add a Docker health check using fipsctl:

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