rakka-inference 0.2.6

Multi-runtime GPU + remote inference as a supervised actor system on the rakka actor runtime.

rakka-inference

One supervised actor topology for every place a model can run. Local GPU runtimes (vLLM, TensorRT, ONNX Runtime, Candle, cudarc, mistral.rs) and managed APIs (OpenAI, Anthropic, Gemini, LiteLLM) sit under the same routing CRDT, the same supervision tree, the same backpressure story. A request doesn't know — and doesn't need to — whether it landed on an H100 two racks away or in another company's data center.

[dependencies]
inference = { version = "0.2", features = ["openai", "anthropic", "candle", "pipeline"] }

use inference::prelude::*;

// Same value object describes a vLLM-on-4×H100 replica or a Gemini Vertex
// deployment. The `runtime` field is the only thing that changes —
// and it's auto-inferred from the model name when omitted.
let dep = Deployment {
    name: "gpt-4o-mini".into(),
    model: "gpt-4o-mini".into(),
    runtime: None,
    runtime_config: None,
    gpus: None,
    replicas: 1,
    serving: Serving::default(),
    budget: None,
    idempotent: true,
};

Built on rakka for actor supervision, clustering, and CRDTs, and on rakka-accel for two-tier GPU supervision. Cost, latency, and reliability stop being three pipelines and become one.

---

Why

Production AI rarely runs only on owned hardware. Frontier models, burst capacity, and compliance edge cases all push work onto managed APIs. Bolting providers onto a separate retry / rate-limit / observability stack from your local GPU pool fragments the system — and the cracks are exactly where 3 a.m. pages come from.

You'd otherwise hand-roll	rakka-inference gives you
One routing layer for local pools, another for the API SDK	Single routing CRDT — gpt-4o and llama-3.1-70b resolve through the same path
Per-process token buckets that 429 on cluster scale-out	RateLimiterActor over rakka_distributed_data::GCounter — one bucket, all nodes
Hand-written retry / breaker / backoff per provider	CircuitBreakerActor + jittered retry + content-filter triage, one strategy
Sticky CUDA-context recovery glued to async tasks	rakka_accel::error::device_supervisor_strategy() adopted unchanged
Cascade graphs duct-taped from threadpools and channels	InferenceCascade / DynamicBatchingServer / ModelReplicaPool actors
Credential rotation that drops in-flight traffic	RemoteSessionActor::rebuild drains old, routes new — zero dropped requests
A no-GPU egress server that still pulls cudarc transitively	--features remote-only ⇒ cudarc, rakka-accel, candle not in the graph
Cost guardrails as Slack alerts after the bill arrives	Budget { max_spend_per_hour_usd, on_exceeded: Reject } enforced at the actor

Every concern that's normally a separate library or a separate incident is folded into one supervised graph with typed messages.

---

30-second tour

# Stand up an OpenAI-compatible gateway over real (or mocked) providers.
cargo run -p inference-cli --features all-remote -- serve --config demo.toml

# End-to-end demo (happy path / 429 retry / circuit-open) without
# spending a cent — wiremock under the hood.
cargo run --bin remote_only_demo

# Pure-remote binary, zero GPU deps in the graph.
cargo build -p inference --no-default-features --features remote-only

---

Architecture

The full design lives in docs/rustakka-inference-architecture-v4.md (1,459 lines, RFC v4). Short version:

                      [HTTP clients]
                            │
                            ▼
                   ApiGatewayActor                   runtime-agnostic
                            │ spawns one per request (inference-runtime)
                            ▼
                    RequestActor
                            │   ask(routing target)
                            ▼
                  DpCoordinatorActor                cluster-singleton
                            │   tell(AddRequest)
                            ▼
            ┌───────────────┴───────────────┐
            ▼                               ▼
   EngineCoreActor (LOCAL)          RemoteEngineCoreActor (REMOTE)
   ┌──────────────────────┐         ┌────────────────────────────┐
   │ scheduler/batcher    │         │ request queue (priority)   │
   │ kv_cache_mgr (LLM)   │         │ rate-limit-aware dispatch  │
   │ ModelExecutorActor   │         │ ┌─────────────────────────┐│
   │   ├─ WorkerActor     │         │ │ WorkerPool              ││
   │   │   └─ ContextActor│         │ │  ├─ RemoteWorkerActor   ││
   │   │       ├─ ModelRunner       │ │  └─ RemoteWorkerActor   ││
   │   │       └─ rakka_accel::*     │ └─────────────────────────┘│
   │   └─ ...                       │ uses:                      │
   └──────────────────────┘         │   RateLimiterActor (CRDT)  │
                                    │   CircuitBreakerActor      │
                                    │   RemoteSessionActor       │
                                    └────────────────────────────┘

The local-GPU tier rides on top of rakka-accel's substrate: DeviceActor, ContextActor, GpuRef<T>, GpuDispatcher, PerActorAllocator, PlacementActor, BlasActor/CudnnActor/etc. We don't reinvent two-tier supervision; we adopt rakka_accel::error::device_supervisor_strategy() and add the inference-specific Box<dyn ModelRunner> slot on top.

The remote-network tier is HTTP/2 + SSE + connection pooling, with distributed rate limiting via rakka_distributed_data::GCounter and circuit breaking + retry/backoff inside inference-remote-core.

---

Crate layout — pick what you need

The workspace is 18 crates plus xtask and the demo. Each layer is optional via Cargo features so you only compile what you use. Three recommended preset shapes:

Preset	What you get	What you skip
remote-only	OpenAI + Anthropic + Gemini + LiteLLM + pipeline + rate-limiting / circuit-breaker / cost tracking	All GPU code (cudarc, rakka-accel, candle, pyo3)
default-prod	vLLM + TensorRT + ORT + OpenAI + Anthropic + pipeline	Other GPU runtimes; LiteLLM; Gemini
all-runtimes	Everything	—

Detailed feature matrix: docs/feature-matrix.md.

inference                                              ← rollup; one dep, feature-flag-driven
   │
   ├── inference-core                                  ← traits, types, no actor / GPU / HTTP deps
   │
   ├── inference-runtime                               ← gateway, request, dp-coordinator,
   │      [feature: local-gpu → rakka-accel]              engine-core, worker (two-tier),
   │                                                    placement, deployment-mgr, metrics
   │
   ├── inference-remote-core                           ← rate limiter (GCounter CRDT),
   │                                                    circuit breaker, retry/backoff,
   │                                                    SSE parser, session lifecycle
   │
   ├── inference-runtime-{openai, anthropic, gemini,   ← per-provider ModelRunner + cost table
   │   litellm}
   │
   ├── inference-runtime-{vllm, tensorrt, ort, candle, ← per-backend ModelRunner; feature-gated
   │   cudarc, mistralrs}                                so absent system libs don't break the
   │                                                    workspace build
   │
   ├── inference-python-bridge                         ← PythonGpuBridge + python-pinned dispatcher
   │      [feature: python → pyo3]                       (will lift to rakka-accel F4 — see TODO)
   │
   ├── inference-pipeline                              ← rakka-streams + re-export of
   │      [feature: cuda-patterns → rakka-accel-patterns] DynamicBatchingServer / InferenceCascade /
   │                                                    ModelReplicaPool / FairShareScheduler /
   │                                                    ModelHotSwapServer / SpeculativeDecoder
   │
   ├── inference-testkit                               ← MockRunner + wiremock-backed provider
   │                                                    mocks (inject_429, inject_5xx, ...)
   │
   ├── inference-cli                                   ← `rakka serve --config <toml>`
   │
   └── inference-py-bindings                           ← PyO3 bindings for Cluster / Deployment
          [feature: python]

How to add only the runtimes you need

# Just OpenAI + Anthropic, no GPU code, no Python:
inference = { workspace = true, features = ["openai", "anthropic", "pipeline"] }

# Local Candle + remote OpenAI fallback:
inference = { workspace = true, features = ["candle", "openai", "pipeline"] }
# (Pulls rakka-accel + cudarc + candle-* automatically via the `candle` feature.)

# Everything, including the testkit:
inference = { workspace = true, features = ["all-runtimes", "testkit"] }

The rollup's job is exactly this: make Cargo.toml declare intent and let the feature graph compute deps.

---

What you don't have to think about

• Two-tier GPU supervision. local-gpu wires WorkerActor / ContextActor to rakka_accel::error::device_supervisor_strategy(). Sticky-error CUDA contexts get Restart; OOM gets Resume; unrecoverable failures Stop. No panic-string parsing in your code.
• Distributed rate limits. RateLimiterActor shares its token-spent log across cluster nodes through rakka_distributed_data::GCounter. Two members calling OpenAI on the same API key collectively respect the bucket — no surprise 429 storms on scale-out.
• Typed circuit-breaker propagation. When the breaker opens, the caller sees InferenceError::CircuitOpen { provider, opened_at_unix_ms, retry_at_unix_ms }. Fall back, surface a 429, or queue — without knowing whether the bottleneck was GPU memory or a remote outage.
• Pipelines from blueprints, not threadpools. Enable cuda-patterns and inference::cuda_patterns::{DynamicBatchingServer, InferenceCascade, ModelReplicaPool, FairShareScheduler, ModelHotSwapServer, SpeculativeDecoder, MoeRouter} are one import away. Plug a closure into ModelRunner::execute and you've composed §9 of the architecture doc.
• Compile-time dependency budgets. cargo build -p inference --features remote-only produces a binary with zero cudarc, zero rakka-accel, zero candle, zero pyo3 in the graph. Layered crates make the invariant load-bearing, not aspirational.
• Hot credential rotation. RemoteSessionActor::rebuild drains in-flight requests on the old credential and routes new ones on the rotated value. Zero dropped traffic.

---

Developer experience

Six layers, surface up to depth

1. Deployment value object. Most users never go deeper. runtime is auto-inferred from model name when omitted (gpt-* → openai, claude-* → anthropic, …).
2. Per-runtime configs. OpenAiConfig, AnthropicConfig, GeminiConfig (Vertex + AI Studio), LiteLlmConfig, CandleConfig, VllmConfig, etc. for explicit overrides.
3. <config>.toml project files. rakka serve --config foo.toml reads the §11.3 schema and applies every [[deployment]].
4. Python decorators. @inference_actor for orchestration actors that compose deployments without touching a GPU directly. Skeleton in inference-py-bindings.
5. Escape hatches. cluster.deployment("gpt-4o").rate_limiter(), .circuit_breaker(), .workers() — direct ActorRefs for incident response (force_open, rebuild_session, etc.).
6. Raw rakka actors. When you need it, you have the full actor system underneath. Unprivileged.

Footgun-resistant by design

• Secrets are typed. inference_core::SecretString (re-export of secrecy::SecretString) — won't Debug, won't Display, never appears in logs.
• Rate-limit validation at deploy time. Catches a deployment claiming rpm = 100_000 against a free-tier API key with a typed error before the first user request hits.
• Network egress checked at deploy time. The placement actor pings the provider from each chosen node before flipping the deployment to Serving.
• Hot-swappable credentials. Updating the secret source triggers RemoteSessionActor::rebuild on the next pulse; in-flight requests drain on the old credential, new ones use the rotated value. Zero dropped traffic.
• Cost guardrails. Budget { max_spend_per_hour_usd, on_exceeded: Reject } on a Deployment makes runaway provider spend physically impossible.

---

Verification

Every PR runs:

cargo build --workspace
cargo build -p inference --features remote-only          # zero GPU deps
cargo build -p inference --features cuda,cuda-patterns   # local + patterns
cargo build -p inference --features all-runtimes
cargo test --workspace
cargo run --bin remote_only_demo

The demo asserts the §13 Phase-1 + Phase-2c exit criteria end-to-end against a wiremock-driven OpenAI mock: happy-path streaming, 429 retry-after, and circuit-breaker open after consecutive 5xx.

---

Status

Layer	Status
Foundation (inference-core)	✅ stable surface; serde round-trips for every RuntimeConfig variant
Runtime-agnostic actors	✅ gateway, request, dp-coordinator, engine-core, worker, placement, manager, metrics
Remote infrastructure	✅ rate limiter (CRDT), strict variant (singleton), circuit breaker, retry, SSE, session
OpenAI / Anthropic / Gemini / LiteLLM	✅ ModelRunner + wire types + error classification + pricing tables
Local Rust-native runtimes	🟡 trait satisfied; forward-pass bodies are stubs pinned to the doc's §13 Phase 2b roadmap
vLLM / TensorRT FFI	🟡 stubs that compile against the trait; full bodies on §13 Phase 2a/2b
Pipeline (rakka-streams + cuda-patterns)	✅ re-export shim + reference hybrid graph
CLI (rakka serve)	✅ TOML config → ActorSystem → gateway; cost-report/rotate-credentials are stubs
Python bindings	🟡 PyO3 skeleton (Cluster, Deployment); decorator surface deferred

---

AI-assisted development

If you're using Claude Code, Cursor, or another AI coding assistant on a project that depends on rakka-inference, install our ai-skills bundle — seven skills covering quickstart, choosing a runtime, wiring remote providers, composing pipelines, deployment, typed-error troubleshooting, and extending with a new backend.

/plugin marketplace add rustakka/rakka-inference
/plugin install rakka-inference-ai-skills@rakka-inference

Each SKILL.md is a thin router into the canonical docs (this README, the per-crate READMEs, the architecture RFC) so the skills stay in sync with the code instead of restating API surfaces that belong in rustdoc. Other harnesses (Cursor, Codex CLI, Gemini CLI, Aider, etc.) have install instructions in ai-skills/README.md.

Companion bundles for the broader stack:

• rakka ai-skills — actor design, supervision, persistence, clustering, Python bindings.
• rakka-accel ai-skills — DeviceActor, kernel selection, two-tier GPU supervision, backend choice.

Install all three when you're building a service that uses rakka primitives, rakka-accel GPU acceleration, and rakka-inference runtimes.

---

Release management

Releases are fully automated. Land a feat: / fix: commit on main and the version-bump workflow tags vX.Y.Z; the release workflow fires on the tag, runs cargo xtask verify, builds binaries for five platforms, generates release notes from git log, and publishes the allowlisted crates to crates.io in dependency order with idempotent retry.

Task	How
Bump + tag based on Conventional Commits	Auto on push to main via .github/workflows/version-bump.yml.
Force a specific version	Release-As: x.y.z in commit footer.
Run the full release pipeline manually	Actions → Release → Run workflow.
Dry-run before tagging	Actions → Release → Run workflow → dry_run: true.
Inspect publishable vs gated crates	cargo xtask release-checklist.
Audit anti-pattern regressions	cargo xtask audit / cargo xtask audit --check.
Run the same checks CI runs	cargo xtask verify.

Full operator runbook: RELEASING.md. Contributor guide: CONTRIBUTING.md.

License

Apache-2.0. See LICENSE once it lands; the workspace inherits the rakka project license.