alknet/docs/architecture/overview.md

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reviewed	2026-06-07

Alknet Overview

Purpose

Alknet is a self-hostable SSH-based tunnel tool that provides VPN-like functionality without being a VPN protocol. It enables:

• Private tunneling of services (Postgres, Redis, internal APIs) over SSH
• Censorship circumvention — SSH over TLS on port 443 looks like HTTPS to DPI
• NAT traversal — iroh transport allows peer-to-peer connections without public IPs or port forwarding
• Service mesh connectivity — a lightweight transport layer for the pubsub/operations event system

The core insight: SSH tunnels work because SSH is fundamental infrastructure. Blocking it breaks the internet. Alknet makes SSH tunneling accessible through a simple CLI with pluggable transports.

Crate Structure

Alknet is decomposed into six crates with a strict acyclic dependency graph (ADR-027):

Crate	Purpose	Exists Now?
alknet-core	Transport, SSH, call protocol, config, auth types, OperationSpec, Interface trait	Yes
alknet-napi	Node.js native addon via napi-rs	Yes
alknet-secret	BIP39, SLIP-0010 HD key derivation, AES-256-GCM, SecretProtocol irpc service	Phase 2+
alknet-storage	SQLite-backed metagraph, identity tables, ACL graph, honker, StorageProtocol	Phase 2+
alknet-flowgraph	FlowGraph<N,E> over petgraph, operation graph, call graph	Phase 2+
alknet (CLI)	Binary that assembles everything with feature flags	Yes

The four library crates (core, secret, storage, flowgraph) are independent of each other. Dependencies flow upward only: the CLI binary sits at the top and wires concrete implementations together. alknet-storage implements alknet-core's IdentityProvider trait without a crate dependency — the CLI binary provides the bridge.

irpc is behind a feature flag in alknet-core. Nodes that only do SSH tunneling don't need the service layer overhead.

Three-Layer Model

Alknet uses a three-layer model (ADR-026, ADR-035):

Layer	Responsibility	Examples
Layer 1: Transport	Produces byte streams (AsyncRead + AsyncWrite + Unpin + Send)	TCP, TLS, iroh, WebTransport (future)
Layer 2: Interface	Two categories: StreamInterface (consumes transport stream, produces session) and MessageInterface (handles discrete requests, manages own transport)	Stream: SSH, raw framing. Message: HTTP, DNS
Layer 3: Protocol	Carries semantics — operation registry, service calls, events	Call protocol, OperationEnv, operation dispatch

SSH is an interface, not a transport. DNS is a message interface, not a transport. The three-layer model enables HTTP interfaces (stealth mode byte-peek), DNS control channels, and local service mesh (raw framing) without wrapping SSH inside those transports.

A stream-based connection is always a (Transport, StreamInterface) pair. Message-based interfaces manage their own transport. The protocol layer is agnostic to both.

Service Layer

The irpc service layer decomposes alknet's core responsibilities into independently testable, deployable, and replaceable components (ADR-033, services.md):

• Auth (AuthProtocol) — verify identities, check credentials
• Secret (SecretProtocol) — derive keys, encrypt/decrypt
• Config (ConfigProtocol) — dynamic config reload
• Storage (StorageProtocol) — graph CRUD, metagraph operations

OperationEnv is the universal composition mechanism. A handler receives context.env.invoke("secrets", "derive", input) and doesn't know whether the dispatch is local (direct function call), in-cluster (irpc service), or cross-node (call protocol EventEnvelope). Three dispatch paths, one handler-facing API.

Phase boundary: Phase 1 ships ConfigIdentityProvider (ArcSwap-backed) and ConfigServiceImpl (ArcSwap-backed) as the only auth and config implementations. The irpc service protocols (AuthProtocol, SecretProtocol, etc.) and the production deployment topology (multi-node with StorageIdentityProvider) are contracted in the specs but will be implemented in Phase 2+. Application services (DockerService, NodeService, agent services) are downstream concerns that build on top of the call protocol and OperationEnv.

Identity

Identity struct and IdentityProvider trait are core types in alknet-core (ADR-029, identity.md):

pub struct Identity {
    pub id: String,          // Fingerprint (config auth) or account UUID (database auth)
    pub scopes: Vec<String>, // Authorization scope strings
    pub resources: HashMap<String, Vec<String>>, // Resource-level authorization
}

IdentityProvider decouples alknet-core from identity storage. Phase 1 ships ConfigIdentityProvider (reads from ArcSwap<DynamicConfig.auth>). StorageIdentityProvider (Phase 2+, backed by SQLite) replaces it for production deployments. Both produce the same Identity result.

Exports

Binary: alknet

A single binary with subcommands:

alknet serve     — Start the server (accepts SSH connections)
alknet connect  — Start the client (opens SSH session, exposes SOCKS5/port-forwards)

Library: alknet-core

The alknet-core crate exports the pluggable components for embedding or programmatic use:

• Transport trait — produces a duplex stream for SSH to run over
• TcpTransport — direct TCP connection
• TlsTransport — TCP + tokio-rustls TLS
• IrohTransport — iroh QUIC P2P connection
• Interface trait → StreamInterface trait and MessageInterface trait (ADR-035)
• InterfaceSession trait — recv()/send() producing/consuming InterfaceEvent frames
• InterfaceRequest / InterfaceResponse — normalized request/response for message interfaces
• Socks5Server — local SOCKS5 proxy that forwards through SSH channels
• PortForwarder — manages local/remote port forwards
• ServerHandler → SshInterface — russh server handler with configurable auth and channel policies
• Identity / IdentityProvider — core identity types (ADR-029)
• CredentialProvider / CredentialSet — outbound credential types (ADR-036)
• OperationSpec — operation registration for call protocol (ADR-025)
• OperationEnv / OperationContext — universal composition and operation context
• ConnectOptions / ServeOptions — programmatic configuration structs
• StaticConfig / DynamicConfig — static/immutable vs, hot-reloadable config (ADR-030)
• ConfigReloadHandle — programmatic reload of dynamic config
• ForwardingPolicy — rule-based allow/deny for channel targets (ADR-031)
• ListenerConfig — stream and message listener configuration

Dependencies

Dependency	Purpose	Crate	Feature-gated
russh	SSH client & server	core	No (core)
tokio	Async runtime	core	No (core)
tokio-rustls	TLS wrapping	core	Yes (tls)
rustls	TLS implementation	core	Yes (tls)
rustls-acme	ACME/Let's Encrypt auto-cert	core	Yes (acme)
iroh	P2P QUIC transport	core	Yes (iroh)
irpc	Streaming RPC service layer	core	Yes (irpc)
arc-swap	Lock-free dynamic config	core	No (core)
serde	Serialization	core	No (core)
clap	CLI argument parsing	CLI	No (CLI)
toml	TOML config file	CLI	No (CLI)
tracing	Structured logging	core	No (core)
anyhow / thiserror	Error handling	core	No (core)
bip39	Mnemonic generation	secret	No (secret)
ed25519-bip32	HD key derivation	secret	No (secret)
aes-gcm	AES-256-GCM encryption	secret	No (secret)
rusqlite	SQLite (via honker)	storage	No (storage)
honker	Event-sourced storage	storage	No (storage)
petgraph	Graph data structure	storage, flowgraph	No
jsonschema	JSON Schema validation	storage, flowgraph	No

Note: tun-rs is no longer a dependency. TUN support is deferred in favor of the external tun2proxy tool (ADR-014).

Architecture Constraints

1. SSH runs over transport, not alongside — The transport layer produces a single AsyncRead+AsyncWrite+Unpin+Send stream. SSH runs over that stream via russh::client::connect_stream() / russh::server::run_stream(). The SSH layer never knows what transport it's on. (ADR-001, ADR-004)

2. Three-layer model: Transport, Interface, Protocol — SSH is a StreamInterface (Layer 2), not a transport (Layer 1). HTTP and DNS are MessageInterfaces (Layer 2). A connection is always a (Transport, StreamInterface) pair for stream-based interfaces, or a standalone MessageInterface for message-based ones. The call protocol (Layer 3) is agnostic to both. This enables HTTP interfaces, DNS control channels, and local service mesh without wrapping SSH. (ADR-026, ADR-035)

3. SOCKS5 is the primary client interface — Port forwarding is built on top of SOCKS5-like channel management. For VPN-like "route all traffic" behavior, users run tun2proxy alongside alknet's SOCKS5 proxy. TUN is not in the project scope. (ADR-005, ADR-014)

4. No logging of tunnel destinations — The server logs auth attempts and connections (for fail2ban) but does not log channel_open_direct_tcpip destinations, DNS lookups, or bytes transferred. (ADR-006, ADR-013)

5. Programmatic-first API — Configuration via CLI flags, library API structs (ConnectOptions, ServeOptions), and environment variables. No ~/.ssh/config parsing. Optional --config TOML file for reproducible deployments. (ADR-011, ADR-030)

6. Feature flags control transport inclusion — tls, iroh, acme, irpc are feature-gated so the base install is lean. Users opt in to heavier dependencies.

7. Authentication is key-based and unified — Ed25519 public key (default) and OpenSSH certificate authority. Same key material for SSH and token auth. Identity resolves through IdentityProvider trait, decoupling core from identity storage. (ADR-012, ADR-023, ADR-029)

8. NAPI exposes both connect() and serve() — The napi-rs wrapper provides client and server functionality, using napi-rs as the FFI bridge. The NAPI layer is transport-agnostic and not tied to pubsub. (ADR-015, ADR-016)

9. Static/dynamic config split — Transport-level settings (listen address, TLS certs) are immutable after startup. Auth, forwarding policy, and rate limits are hot-reloadable via ArcSwap<DynamicConfig>. (ADR-030)

10. Forwarding policy enforced before proxy spawn — Each channel_open_direct_tcpip is checked against ForwardingPolicy before a TCP connection is made. Default-allow preserves current behavior. (ADR-031)

11. OperationEnv as universal composition mechanism — Handlers call context.env.invoke(namespace, op, input) regardless of dispatch path (local, irpc service, remote call protocol). (ADR-033)

12. Event boundary discipline — Domain events (Honker streams) stay within the owning service. irpc calls are synchronous and in-cluster. Call protocol EventEnvelope is the only thing that crosses node boundaries. (ADR-032)

13. Error handling follows a consistent layered pattern — Transport and auth errors cause reconnection (client, with exponential backoff) or connection rejection (server). Channel-level errors (target unreachable, proxy failure) close the individual channel without killing the session. Library API errors propagate via anyhow::Result / thiserror types. CLI reports errors to stderr with appropriate exit codes. NAPI errors are marshalled as JavaScript exceptions.

Design Decisions

ADR	Decision	Summary
001	Pluggable transport	Transport trait produces AsyncRead+AsyncWrite+Unpin+Send, SSH consumes it
002	TUN shim separate	Superseded — TUN is deferred, use tun2proxy (ADR-014)
003	iroh stream join	tokio::io::join(recv, send) combines QUIC halves
004	SSH over transport	SSH never accesses TCP/iroh/TLS directly
005	SOCKS5 first	SOCKS5 is the primary interface; TUN is external (tun2proxy)
006	No logging of tunnel destinations	Server logs auth and connections, not destinations
007	NAPI single stream	NAPI exposes duplex streams, not SSH multiplexing
008	ACME/Let's Encrypt	Auto-provision TLS certs, domain and IP paths
009	Default iroh relay	n0 relay by default, --iroh-relay override
010	Transport chaining	--proxy works with all transports natively
011	Programmatic-first	No SSH config files; options are structs, env vars, CLI flags (amended by ADR-030 for optional TOML)
012	Key + cert-authority	Ed25519 keys + OpenSSH CA; no password auth
013	Fail2ban-friendly	Structured auth logs + built-in rate limiting
014	Defer TUN	Use tun2proxy for VPN-like behavior; no alknet-tun binary
015	napi-rs	Standard Node.js native addon tooling
016	connect + serve	NAPI exposes both client and server from the start
017	Stealth mode	Protocol multiplexing on port 443
018	Control channel	Reserved alknet-control destination for pubsub
019	Proxy dual semantics	--proxy routes transport on client, data on server
023	Unified auth	Same key material for SSH and token auth
024	Bidirectional call protocol	Both sides can initiate calls
025	Handler/spec separation	Downstream registers operations without modifying core
026	Three-layer model	SSH is Layer 2, not Layer 1
027	Crate decomposition	Six crates, acyclic deps, feature-gated irpc
028	Auth as irpc service	IdentityProvider is the contract, irpc is one backend
029	Identity as core type	Identity and IdentityProvider in alknet-core
030	Static/dynamic config	ArcSwap for hot-reloadable auth and forwarding
031	Forwarding policy	Per-identity, per-destination, per-transport rules
032	Event boundary	Domain events never cross service boundaries
033	OperationEnv	Universal composition, three dispatch paths
034	Head/worker	Replaces hub/spoke terminology
035	StreamInterface/MessageInterface	Two Layer 2 trait categories for stream vs message
036	CredentialProvider as core type	Outbound credentials in alknet_core::credentials
037	API keys in DynamicConfig	Hash-verified bearer tokens for service accounts

Open Questions

See open-questions.md for all open and resolved questions. Key open questions: OQ-15 (QUIC coexistence), OQ-19 (WebTransport TLS), OQ-20 (worker registration), OQ-IF-01 (Interface session / EventEnvelope relationship).

References

• transport.md — Transport abstraction (Layer 1)
• interface.md — StreamInterface and MessageInterface (Layer 2)
• call-protocol.md — Call protocol (Layer 3)
• auth.md — Unified authentication, API keys, credential presentation
• identity.md — Identity and IdentityProvider
• credentials.md — CredentialProvider and CredentialSet (outbound auth)
• definitions.md — Terminology disambiguation
• configuration.md — StaticConfig, DynamicConfig, ForwardingPolicy
• services.md — irpc service layer, OperationEnv
• server.md — Server acceptance, channel handling
• client.md — Client connection, SOCKS5, port forwarding
• napi-and-pubsub.md — NAPI wrapper and pubsub adapter
• storage.md — alknet-storage: metagraph, identity, ACL
• flowgraph.md — alknet-flowgraph: call graph, operation graph
• secret-service.md — alknet-secret: BIP39, SLIP-0010, AES-GCM
• Feasibility Assessment
• russh API — SSH client/server library
• Dispatch — Reference implementation of russh port forwarding
• iroh — P2P QUIC connections
• tun2proxy — Recommended external TUN-to-SOCKS5 tool
• irpc — iroh streaming RPC
• Production certbot setup — Let's Encrypt on our infrastructure
• Production fail2ban setup — fail2ban with nftables on our infrastructure