61 lines
2.9 KiB
Markdown
61 lines
2.9 KiB
Markdown
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# ADR-004: Tor Hidden Services for Peer Communication
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**Status**: Accepted (2026-03) — **partially superseded in practice, see
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Amendment below**
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**Date**: 2026-03
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## Context
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Federated nodes need to communicate directly for state sync, app deployment, and peer verification. Options: direct IP, VPN tunnel, Tor hidden services, I2P.
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## Decision
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Use Tor hidden services (.onion addresses) for all inter-node communication.
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## Consequences
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### Positive
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- **NAT traversal**: Works behind any firewall or NAT without port forwarding
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- **IP privacy**: Nodes never expose their real IP addresses to each other
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- **End-to-end encryption**: Tor provides encryption without additional TLS setup
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- **Censorship resistance**: Onion routing makes traffic analysis difficult
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- **Stable addressing**: .onion addresses persist across IP changes and network migrations
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- **No central infrastructure**: No VPN server, STUN/TURN server, or relay needed
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### Negative
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- **Latency**: Tor adds 200-500ms per hop; 3 hops per direction = noticeable delay
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- **Bandwidth**: Tor network has limited bandwidth; not suitable for bulk data transfer
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- **Reliability**: Tor circuits can break; connections may need retry logic
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- **Setup complexity**: Requires running a Tor daemon (`archy-tor` container)
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- **Blocked networks**: Some networks block Tor; bridges can help but add complexity
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### Mitigation
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- Use Tor only for RPC/control plane; bulk data (container images) pulled from registries
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- Implement retry with backoff for Tor connections
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- Container `archy-tor` runs automatically with host networking for hidden service access
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- Federation sync interval (5 min) tolerates occasional connection failures
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## Amendment (recorded 2026-08)
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Two things in this ADR no longer describe the system. Both changes happened
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without their own ADR, which is itself worth noting.
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**1. Tor is no longer used for *all* inter-node communication — it is the last
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fallback.** The transport layer now tries, in order, mesh radio → LAN → FIPS
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overlay → Tor (`transport::TransportKind`, priority 1–4). The latency and
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bandwidth costs listed above are exactly why: FIPS was introduced to carry WAN
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peering that Tor made too slow, and direct LAN peering skips the overlay
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entirely for co-located nodes. Tor's NAT-traversal and IP-privacy properties are
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still what make it the dependable floor when the others are unavailable.
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**2. Tor does not run as the `archy-tor` container.** It is the host's Debian
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`tor` package, running as `debian-tor` and driven by the
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`archipelago-tor-helper` path unit (`scripts/tor-helper.sh`), which installs a
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staged `/etc/tor/torrc` and restarts the service. The migration was deliberate
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and is still enforced: `scripts/container-doctor.sh` removes an `archy-tor`
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container if it finds one and switches the node to system Tor. There is no
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`apps/tor` manifest.
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The decision to use onion services for peer reachability stands; only its
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exclusivity and its packaging changed.
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