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SlimFaas

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SlimFaas : The slimmest and simplest Function As A Service

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    <a href="https://slimfaas.dev">Go to SlimFaas website</a>
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# SlimFaas: The Slimmest, Simplest & Autoscaling-First Function-as-a-Service

### 🌥️ Proud CNCF Landscape Project

SlimFaas is part of the [Cloud Native Computing Foundation (CNCF) landscape](https://landscape.cncf.io).

[Join us on CNCF Slack](https://cloud-native.slack.com/archives/C08CRC77VDE) · [Community Meeting Calendar](https://calendar.google.com/calendar/embed?src=be1dd72d18650490580a7d5d96a45a6eebe0fc4c9fe8adce630754cbb6121cca%40group.calendar.google.com&ctz=Europe%2FParis) · [Code of Conduct](https://github.com/cncf/foundation/blob/main/code-of-conduct.md)

</div>

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SlimFaas is a lightweight, plug-and-play Function-as-a-Service (FaaS) platform for Kubernetes (and Docker-Compose / Podman-Compose).
It’s designed to be **fast**, **simple**, and **extremely slim** — with a very opinionated, **autoscaling-first** design:
- `0 → N` wake-up from HTTP history & schedules,
- `0 → N` wake-up from **Kafka lag** via the companion **SlimFaas Kafka** service,
- `N → M` scaling powered by PromQL,
- internal metrics store, debug endpoints, and scale-to-zero out of the box.
- built-in **User Interface** at the SlimFaas root address to see functions, jobs, queues, and real-time messages.
- temporary **Data Files** endpoints to ingest and stage binaries (from tiny to very large) with TTL-friendly storage — perfect for caching & agentic workflows.
- temporary **Data Sets** endpoints (`/data/sets`) to store small, Redis-like KV payloads (cache, JSON state, flags) with optional TTL — replicated through the cluster via a robust consensus layer.

> **Looking for MCP integration?**
> Check out **[SlimFaas MCP](https://slimfaas.dev/mcp)** — the companion runtime that converts *any* OpenAPI definition into MCP-ready tools on the fly.

---

## Why Use SlimFaas?

### 🚀 Autoscaling that actually understands your traffic

- **Scale-to-zero & wake-up**
    - Scale down to `0` after inactivity with configurable timeouts.
    - Wake up from `0 → N` based on real HTTP traffic and/or cron-like schedules.
    - Wake up from `0 → N` based on **Kafka topic activity**, using **SlimFaas Kafka** to monitor consumer lag and call the SlimFaas wake-up API.
    - Control initial capacity with `ReplicasAtStart` to reduce cold-start impact.

- **Two-phase scaling model**
    - **`0 → N`**: driven by HTTP history, schedules, **and Kafka lag (SlimFaas Kafka)** to bring functions online only when they’re needed.
    - **`N → M`**: driven by a built-in PromQL mini-evaluator on top of an internal metrics store.
    - Metrics-based autoscaling only runs when at least one pod exists — no reliance on non-existent metrics.

- **PromQL-driven autoscaler**
    - Express scaling rules with PromQL-style queries, for example:
        - `sum(rate(http_server_requests_seconds_count{namespace="...",job="..."}[1m]))`
        - `max_over_time(slimfaas_function_queue_ready_items{function="my-func"}[30s])`
        - `histogram_quantile(0.95, sum by (le) ( rate(http_server_requests_seconds_bucket{...}[1m]) ))`
    - Choose whether thresholds are **per pod** (`AverageValue`) or **global** (`Value`).
    - Configure scale-up/scale-down policies and stabilization windows inspired by HPA/KEDA.

- **Integrated metrics scraping**
    - SlimFaas scrapes only the Prometheus-style HTTP metrics endpoints of pods with `prometheus.io/scrape: "true"`.
    - It stores only the **metric keys that are requested** in autoscaling triggers or debug queries.
    - A single designated node scrapes and persists metrics; all other nodes read from the same store.

- **Debug-friendly**
    - `POST /debug/promql/eval` – evaluate a PromQL expression against the internal store and see the scalar result.
    - `GET /debug/store` – inspect what metrics are being scraped, how many series exist, and retention size.
    - Designed so you can easily answer: *“What does SlimFaas see when it decides to scale?”*

- **FinOps-minded**
    - 30-minute metrics retention window for predictable memory usage.
    - Native scale-to-zero and schedules to keep non-critical workloads cold when they’re not needed.
    - Slim control-plane footprint to avoid burning resources in your autoscaling logic itself.

### 🧵 Synchronous and Asynchronous Functions

- Simple HTTP endpoints for both **sync** and **async** calls.
- Async mode:
    - Limit the number of concurrent requests per function.
    - Configure retry behaviors and backoff strategies.
    - Drive autoscaling decisions from queue metrics.

### ⏱ Jobs

- Run **one-off**, **batch**, and **scheduled (cron)** jobs via HTTP calls.
- Configure:
    - concurrency,
    - visibility (public/private),
    - retry behavior.

### 🔐 Private/Public Functions and Jobs

- Mark functions as **public** or **private**:
    - Private: only accessible from within the cluster or from trusted pods.
    - Public: fronted by Ingress / API Gateways as usual.

### 📣 Publish/Subscribe Internal Events

- Synchronously send events to **every replica** of selected functions.
- No additional event bus required — ideal for cluster-local fan-out, cache invalidation, configuration refresh, etc.

### 🧰 Data Files & Data Sets (real-time ingestion + ephemeral caching + robust KV)

SlimFaas includes two complementary “data” APIs:

#### 📁 Data Files (temporary binary artifacts)

**Data Files** endpoints are designed to **stream, store, and serve temporary files** — from tiny payloads to *very large* binaries.
Ideal for **agentic workflows** and **real-time ingestion**: upload once, get an `id`, then let tools/functions consume it when they’re ready.

- Stream-first uploads (without buffering in memory or disk)
- **Agentic-ready** attachments & multi-step flows
- **Ephemeral caching** for intermediate artifacts
- **TTL-based** lifecycle (auto-expiration)

#### 🧠 Data Sets (Redis-like KV for small state)

**Data Sets** endpoints provide a **small, Redis-like KV store** (raw bytes) replicated across the SlimFaas cluster.

- Stream-first uploads
- Store **anything small**: JSON, strings, flags, lightweight cache entries
- Optional `ttl` in **milliseconds** (auto-expiration)
- Hard limit: **1 MiB per value**

### 🧠 “Mind Changer” (Status & Wake-up API)

- Built-in REST APIs to:
    - monitor function and replica status,
    - wake functions up on demand,
    - integrate autoscaling state into your own tools/dashboards.

### 🔌 Plug and Play

- Deploy SlimFaas as a standard pod/StatefulSet with minimal configuration.
- Onboard existing workloads simply by adding annotations:
    - let SlimFaas manage their scaling without rewriting your applications.

### ⚡ Slim & Fast

- Written in .NET with:
    - focus on performance and low memory footprint,
    - AOT-friendly design,
    - minimal dependency surface.

---

## Ready to Get Started?

Check out:

- [Get Started](docs/get-started.md) – Deploy SlimFaas on Kubernetes or Docker Compose.
- [Local Mode](docs/native-local-mode.md) – Run functions, Jobs, development processes, and a supervised SlimFaas cluster directly on your machine.
- Scaling
    - [Autoscaling](docs/autoscaling.md) – Configure `0 → N` / `N → M` autoscaling, PromQL triggers, metrics scraping, and debug endpoints.
    - [Kafka Connector](docs/kafka.md) – Use Kafka topic lag to wake functions and keep workers alive while messages are flowing.
    - [Planet Saver](docs/planet-saver.md) – Start and monitor replicas from a JavaScript frontend.
- Functions & Workloads
    - [Functions](docs/functions.md) – Call functions synchronously or asynchronously.
    - [User Interface](docs/user-interface.md) – Monitor functions, queues, jobs, and real-time messages.
    - [Clients](docs/clients.md) – Integrate SlimFaas with .NET and Python applications.
    - [Events](docs/events.md) – Use internal publish/subscribe events.
    - [Jobs](docs/jobs.md) – Define, schedule, and run one-off jobs.
    - [OpenTelemetry](docs/opentelemetry.md) – Enable distributed tracing, metrics, and logs.
    - [Benchmarks](docs/benchmarking.md) – Measure sync overhead, async delivery latency, and native-local scaling speed.
- Data & Files
    - [Data Files](docs/data-files.md) – Ingest, store, and serve temporary binary artifacts.
    - [Data Sets](docs/data-sets.md) – Store replicated, Redis-like key-value payloads with optional TTL.
- [How It Works](docs/how-it-works.md) – Understand SlimFaas architecture and request flows.
- [MCP](docs/mcp.md) – Convert OpenAPI definitions into MCP-ready tools.

### Technical references

- [Local three-node orchestrator](docs/local-orchestrator.md)
- [Memory profiling](docs/memory-profiling.md)
- [Unified SlimData mutation batching](docs/slimdata-unified-batching.md)
- [SlimData batch modes](docs/slimdata-batch-modes.md)
- [Environment-variable breaking changes](docs/BREAKING_CHANGES_ENVIRONMENT_VARIABLES.md)

We hope SlimFaas helps you **simplify autoscaling**, **reduce costs**, and **keep your serverless workloads slim**.

---

### Community & Governance

- **Community Meeting**
  Join us through our [Community Meeting Calendar](https://calendar.google.com/calendar/embed?src=be1dd72d18650490580a7d5d96a45a6eebe0fc4c9fe8adce630754cbb6121cca%40group.calendar.google.com&ctz=Europe%2FParis)
    - [ICS file](https://calendar.google.com/calendar/ical/be1dd72d18650490580a7d5d96a45a6eebe0fc4c9fe8adce630754cbb6121cca%40group.calendar.google.com/public/basic.ics)

- **Slack Channel**
  Join our channel on the [CNCF Slack](https://cloud-native.slack.com/archives/C08CRC77VDE) to connect with other SlimFaas users.

- **Code of Conduct**
  SlimFaas follows the [CNCF Code of Conduct](https://github.com/cncf/foundation/blob/main/code-of-conduct.md).

Enjoy SlimFaas!

---

## Adopters

List of organizations using this project in production or at stages of testing.

---

Add your logo via a pull request:

- Logo must be in PNG format, 100 px wide and 100 px high.
- Add your logo to the `docs/adopters_logo` folder.

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