Tyn

A minimal Rust microkernel purpose-built for the BEAM.

No Linux. No POSIX. Your Erlang/Elixir code on bare metal.

Recent: the BEAM now runs confined in ring 3 (isolated from the kernel); in-guest TLS works both directions; deploying your own app is one command (tyn deploy). See CHANGELOG.md.

What is Tyn?

Tyn is a unikernel: a single-purpose OS kernel that hosts exactly one thing — the BEAM virtual machine. It replaces the entire Linux stack with ~8,000 lines of Rust, and runs on KVM/QEMU and on real AWS Nitro EC2, driving the network with a from-scratch ENA driver and serving HTTP directly from the kernel.

The BEAM already has its own scheduler, process model, memory management, and distribution. A general-purpose kernel underneath duplicates most of that. Tyn removes the redundancy and gives the BEAM a host built for it and nothing else.

It runs the real, unmodified ERTS — not a reimplementation. A new OTP release should just work. That's the deliberate bet: reimplementing the BEAM (as LING did on Xen) means owning a moving target forever — the SMP scheduler, the JIT, distribution. Hosting upstream ERTS keeps all of that upstream.

Why

• Security — a general-purpose kernel carries drivers and subsystems a cloud BEAM workload never touches. Tyn includes only what the BEAM needs, so the trusted computing base is a few thousand lines of Rust. And it's now enforced, not just small: the BEAM runs in ring 3, isolated from the kernel by a hardware boundary, so a memory-safety bug in the BEAM or a NIF can't reach the kernel. See What works.
• Simplicity — a Tyn image is BEAM bytecode plus the Rust kernel. No OS services, no package manager, no user accounts. The application and its runtime, nothing else.
• Density — images are megabytes, not gigabytes. More nodes per host, lower cost.
• Verifiability — one runtime and a small TCB, structured so formal verification is tractable.

Status

A stock mix phx.new Phoenix app — static assets, LiveView, sessions, outbound HTTP — runs unmodified on OTP 27 BEAM on real AWS Nitro. It serves HTTP under concurrency with byte-exact assets, over a from-scratch ENA driver and network stack — no Linux, no host networking. The BEAM runs confined in ring 3 (see What works).

The serving path is ENA hardware → admin queue → I/O queues → smoltcp → DHCP → gen_tcp → Bandit → Phoenix, entirely inside the Rust kernel — the kernel talks to the NIC's descriptor rings directly.

Throughput figures are omitted here pending a faithful Nitro benchmark. Early numbers were taken under QEMU/SLIRP, whose host networking distorted them; single-connection bulk HTTP/HTTPS on Nitro is ~13 MB/s, but a full benchmark will be published when it's run.

Try it

Run the demo — a public AMI in us-east-1, no build required:

aws ec2 run-instances --image-id ami-0c13cb4a868a6e441 \
    --instance-type c5.large --region us-east-1
# open TCP 8080 in your security group; the instance takes ~1–2 min to launch
# (Tyn itself boots in ~5 s — the rest is EC2 provisioning), then:
curl http://<public-ip>:8080/                           # → Phoenix landing page
curl -s http://<public-ip>:8080/assets/app.js | wc -c    # → a static asset via kernel sendfile
# open http://<public-ip>:8080/counter in a browser — the LiveView counter increments live

Deploy your own app — one command takes a Mix release to a running instance:

tyn deploy --env DATABASE_URL=... my_app/    # release → AMI → running Nitro instance

It packs the release, builds and imports the image, registers the AMI (reused on unchanged redeploys), launches, and prints the IP and how to reach it. The full walkthrough — IAM policy, security groups, the IAM-gated serial console, config/secrets — is in docs/DEPLOY.md. Instances accrue hourly charges; terminate when done.

What works

• Full Phoenix stack, stock app — a mix phx.new app runs unmodified: static assets (Plug.Static / send_file over kernel sendfile(2), no dependency patch), interactive LiveView (WebSocket mount + live updates), runtime.exs, signed cookies / CSRF / Phoenix.Token, and outbound TCP/UDP + DNS. Clean-clone validated byte-exact on Nitro; codified in tests/.
• BEAM confined in ring 3 — the BEAM runs as ring-3 userland with the kernel in ring 0 behind a hardware boundary: US/NX page permissions, SMEP/SMAP, and a syscall path that bounds-checks every user pointer. A memory-safety bug in the BEAM or a NIF faults and is contained; the kernel keeps serving. Proven by violation — a deliberate BEAM write to a kernel address is denied and contained, and the confused-deputy case (handing the kernel a bad pointer) is rejected — on 16-vCPU Nitro. This confines the kernel from the BEAM; the JIT region is necessarily user-RWX, so it doesn't internally harden the BEAM, and side-channel (Meltdown/Spectre) isolation is future work.
• One-command deploy — tyn deploy takes a Mix release to a running Nitro instance: packs it, builds/imports/registers the AMI (content-hashed, so unchanged redeploys skip the ~10-min import), launches, injects config/secrets via --env, and reports the IP. tyn iam-policy prints the required IAM, and a preflight fails early on missing permissions. A bash wrapper over tyn-pack + the AWS CLI.
• 8-way SMP — ACPI/MADT CPU discovery, APIC timer calibration, AP trampoline (16→64-bit), per-CPU GDT/TSS/IST, per-CPU GS_BASE syscall data, IPI wakeup, preemptive user-mode scheduling.
• BeamAsm JIT — OTP 27 built --enable-jit. The timer preempts inside mmap'd JIT pages; erlang:system_info(emu_flavor) returns jit.
• TCP/UDP networking — gen_tcp / gen_udp end-to-end: POSIX socket layer → smoltcp → virtio-net (QEMU) or the from-scratch ENA driver (Nitro). On Nitro the address comes from DHCP, with lease renewal.
• In-guest TLS, inbound and outbound — HTTPS both terminates and originates inside the guest, with no plaintext hop to an edge terminator. Inbound: the tyn_tls rustls NIF behind a ThousandIsland transport, wired in config-only (no Bandit or app changes). Outbound: OTP's own :ssl does verified client TLS — :httpc / Finch / Postgrex just work — via Tyn's RustCrypto NIF (ECDHE + ECDSA/RSA-PSS/Ed25519 verify) and a pure-Erlang asn1 shim. Both proven on Nitro: TLS 1.3, cert-verified, byte-exact; verify passes a 22/22 adversarial suite. See docs/IN_GUEST_TLS.md. Unreviewed; TLS 1.2/mTLS not yet done — see Limitations.
• :crypto — a from-scratch Rust NIF (RustCrypto primitives) fed by a kernel CSPRNG (RDSEED → ChaCha20), statically linked into ERTS. Passes known-answer vectors and matches upstream OTP byte-for-byte. Unreviewed — see Limitations.
• Distributed Erlang (basic, two-node) — net_kernel distribution works node-to-node on Nitro: mutual connect_node, rpc, large-term transfer byte-exact, tick/nodedown. Needs static host mapping — no in-guest .internal DNS — so it's a fixed pair, not turnkey multi-node. Single-node is the default.
• AWS Nitro deployment — boots from a GRUB/multiboot disk image imported as an EBS snapshot. The ENA NIC (1d0f:ec20) is found via port-IO PCI config, since Nitro publishes no MCFG/ECAM.
• Live eval shell — over the AWS serial console (IAM-gated, no open port) or TCP. Evaluate Erlang or Elixir against the running BEAM.
• Elixir 1.18.3 on OTP 27.
• ~50 Linux syscalls — mmap, read, write, open, stat, pipe, ppoll, futex, clone, epoll, readv, writev, sendfile, getrandom, …
• VFS — read-only cpio (newc) holding the OTP + Elixir .beam files; application images are packed by tyn-pack.
• Boot — Multiboot1, ELF loader for static musl binaries, a 2 MiB/4 KiB page hierarchy with guard pages under kernel stacks.

>> erlang:system_info(emu_flavor).
jit
>> 'Elixir.System':version().
<<"1.18.3">>

Limitations

Tyn is a specialized runtime, and these are first-class, not footnotes. Two kinds: by design — deliberate consequences of hosting one workload on KVM/Nitro — and rough edges — real gaps being closed. Read both before deploying.

By design

• Writable storage is in-memory only. /tmp and /dev/shm are a volatile tmpfs (4 MiB cap, lost on reboot), so Plug.Upload and scratch writes work within that budget. The application VFS is a read-only cpio; there is no persistent disk.
• IPv4 only. IPv6 socket binds are rewritten to IPv4-any at boot (stock Phoenix runtime.exs binds IPv6-any).
• Runs on KVM or Nitro, not QEMU-TCG. Under software emulation (-accel tcg) some images deterministically #PF at boot. Real hardware (Nitro, or KVM with -enable-kvm) is unaffected and is the standard of evidence.
• Wall clock is kvmclock-backed on Nitro/KVM, RTC-seeded elsewhere. On Nitro/KVM, CLOCK_REALTIME uses the paravirtual clock — nanosecond resolution, host-drift-corrected. Where kvmclock isn't exposed it falls back to an RTC-seeded, TSC-extrapolated clock: real UTC but second-resolution and drifts over long uptime. Monotonic time is exact.

Working on it

• Crypto and TLS are unreviewed. The :crypto and TLS NIFs (RustCrypto primitives, kernel-CSPRNG-fed) pass known-answer vectors and match upstream OTP byte-for-byte, and verify — the silent-MITM keystone — is adversarially tested, but the surface has had no outside security review. Don't rely on it for production security until it has (RNG-review first). TLS 1.2 and mTLS aren't done. Boot panics without a hardware RNG (RDRAND/RDSEED; present on c5/m5/t3 Nitro).
• Clustering is not turnkey. Two-node distribution is validated but needs static host mapping (no in-guest .internal DNS). Fine for a fixed pair; not drop-in multi-node discovery.
• Confinement is against memory-safety faults, not side channels. Ring-3 isolation protects the kernel from a BEAM memory bug (proven), but doesn't yet defend Meltdown/Spectre-class side channels — that needs separate page tables (KPTI), which is future work. The JIT region is user-RWX by necessity, so the BEAM isn't internally W^X-hardened.
• No built-in observability yet. Logs and BEAM stats are reachable over the eval shell / serial console, but there's no logs-off-the-box or metrics endpoint yet — operating a deployed instance is hands-on. Deployment (tyn deploy) is done; lifecycle/observability tooling is next.
• LiveView on a bare IP needs check_origin. Phoenix returns 403 on the LiveView WebSocket when the served host doesn't match the configured URL host. check_origin: false is fine for a throwaway IP demo, but for production set the real host list — false is a cross-site WebSocket-hijacking hole on a real deployment.

Architecture

┌─────────────────────────────────────────┐
│  Applications (Elixir / Erlang)         │
├─────────────────────────────────────────┤
│  OTP / Supervision Trees                │
├─────────────────────────────────────────┤
│  ERTS / BEAM VM (unmodified · SMP · JIT)│   ring 3
├─────────────────────────────────────────┤
│  BEAM Host Interface (Rust)             │   ← syscall boundary
│  ~50 Linux syscalls emulated            │     (pointer-checked)
├─────────────────────────────────────────┤
│  Tyn Kernel (Rust · ~8,000 LOC)         │   ring 0
│  SMP · Memory · Networking · VFS · I/O  │
├─────────────────────────────────────────┤
│  KVM / QEMU / AWS Nitro                 │
└─────────────────────────────────────────┘

ERTS is built from unmodified OTP 27 source — no patches, no special defines — via the pinned, reproducible build in beam-build/ (Alpine 3.19, GCC 13.2, musl 1.2.4, static, --enable-jit --without-ssl).

Deeper detail: module structure · boot flow · runtime architecture.

Building & running

Prerequisites

• Rust — the toolchain is pinned in rust-toolchain.toml; rustup installs it on first build.
• A C toolchain — build-essential or equivalent; rustc needs cc to link build scripts and proc-macros.
• QEMU with KVM (qemu-system-x86_64) — for local runs; use -enable-kvm, not TCG.
• A static beam.smp + the OTP/Elixir rootfs cpio — both committed (src/beam.smp.elf, src/otp-rootfs.cpio), so the kernel builds out of the box. To rebuild, see docs/BUILDING_ERTS.md.

Build

cargo build --release --target x86_64-tyn.json \
  -Zbuild-std=core,alloc,compiler_builtins \
  -Zbuild-std-features=compiler-builtins-mem

Run

qemu-system-x86_64 \
  -kernel target/x86_64-tyn/release/tyn-kernel \
  -m 2560M -machine q35 -cpu host -enable-kvm -smp 8 \
  -nographic -no-reboot -serial mon:stdio \
  -device virtio-net-pci,netdev=net0,disable-legacy=on,disable-modern=off \
  -netdev user,id=net0,hostfwd=tcp::5555-:8080,hostfwd=tcp::5567-:9090

The committed image boots a minimal bench app — small endpoints to confirm the kernel boots, serves, and runs the BEAM. It's not the full Phoenix demo; the stock-phx.new app is what the public AMI runs and what you get by deploying your own app. Once the serial console prints phoenix_listening:

curl http://localhost:5555/          # landing page (endpoint list)
curl http://localhost:5555/health    # → {"status":"ok"}
curl http://localhost:5555/json      # live BEAM stats
nc localhost 5567                    # eval shell

Use KVM (-enable-kvm), not TCG. Software emulation deterministically #PFs at boot on some images, and QEMU/SLIRP host networking was the bottleneck behind every early throughput figure. Benchmark on KVM or Nitro.

Testing

tests/ holds the capability suite. Every assertion checks content, not status codes — a truncated asset served as 200 is exactly the bug class this exists to catch.

tests/setup-test-app.sh      # builds a stock mix phx.new app; fails if any dep is patched
tests/run.sh <instance-ip>   # byte-exact assertions; non-zero exit gates a build

It covers byte-exact static assets, large transfers spanning many TX windows, inline and multi-send bodies, N=25 concurrency with per-response hashes, and interactive LiveView.

Engineering record

The bug-class hunts behind the current state, kept because the negative results are as useful as the fixes:

• docs/SEND_CORRUPTION.md — the TCP send-path corruption hunt: eliminated hypotheses, the non-perturbing trace that localized it, and the sys_writev partial-write root cause.
• docs/FUTEX_HISTORY.md — the boot-path futex valve: the init-time thread-progress hazard and the ledger of rejected hypotheses.
• BUGS.md (BUG-1) — the SMP corruption residual: a missing IST on the wakeup IPI let its interrupt frame land in the BEAM red zone under SMP. Fixed, and later dissolved outright by the ring-3 rework (the clean-stack transition removes the red-zone hazard by construction).

Design principles

• Run the real BEAM — the actual ERTS, cross-compiled for Tyn's host interface, not a reimplementation. The BEAM's hard parts (SMP scheduler, JIT, GC, distribution) stay upstream.
• Minimal kernel, maximal BEAM — the kernel provides memory, interrupts, device access, and network. The BEAM does its own scheduling, memory management, code loading, and supervision.
• Target KVM/virtio and Nitro — standardized virtual hardware means a handful of small drivers; each NIC driver is a few hundred lines of Rust.
• Built for verification — minimal unsafe, explicit invariants, a small and now enforced TCB.

Prior art

• LING — Erlang on Xen. Proved the concept; reimplemented the BEAM and targeted only Xen.
• Nerves — Elixir on embedded Linux. Complementary: Nerves owns embedded, Tyn targets cloud.
• GRiSP — BEAM on RTEMS for IoT hardware.
• Asterinas — Rust Linux-compatible kernel; architectural reference.
• rcore-os/virtio-drivers · smoltcp — used by Tyn.

Related projects

• Vor — a BEAM-native language with compile-time verification.
• VorDB — a CRDT-based distributed database built on Vor.

License

MIT OR Apache-2.0