OpenFaaS (Functions as a Service) is an open-source framework that makes it simple to deploy serverless functions and existing microservices to Kubernetes or Docker Swarm. Its design philosophy emphasizes simplicity and developer experience: any process that can be packaged in a Docker container can be deployed as a function on OpenFaaS, supporting any programming language or binary. This container-first approach avoids the language-specific constraints of many FaaS platforms and makes it straightforward to migrate existing services to a serverless model.

OpenFaaS provides a complete function lifecycle: a CLI and UI for building, deploying, and invoking functions; an API gateway that handles routing, metrics collection, and auto-scaling; a built-in Prometheus-based auto-scaler that scales functions from zero to many replicas based on request rate or queue depth; and an asynchronous invocation system backed by NATS Streaming for long-running tasks. Functions are defined using templates that provide language-specific scaffolding, with official templates for Node.js, Python, Go, Java, C#, Ruby, and PHP. The watchdog component handles HTTP request/response mediation between the gateway and function processes.

OpenFaaS has been adopted by developers and organizations seeking a simpler alternative to Knative for running functions on Kubernetes. Its lower operational complexity and gentle learning curve make it popular for smaller teams and edge computing scenarios. OpenFaaS Ltd offers OpenFaaS Pro with enhanced auto-scaling, single sign-on, Kafka event connector, and dedicated support.

Key Capabilities

  • Any Container as a Function - Deploy any Docker container as a serverless function, supporting all languages, frameworks, and binaries
  • Auto-Scaling - Prometheus-driven scaling from zero to thousands of replicas based on requests per second or queue depth
  • Async Invocations - Built-in asynchronous function execution via NATS for long-running tasks with callback support
  • Developer CLI - faas-cli for building, pushing, deploying, and invoking functions with YAML-based stack definitions

Cloud Equivalents

OpenFaaS is the open-source alternative to AWS Lambda, Azure Functions, and Google Cloud Functions. Cloud FaaS platforms offer deeper ecosystem integration and true pay-per-invocation pricing, while OpenFaaS provides language-agnostic function deployment on any Kubernetes cluster with no cold start penalties for pre-scaled functions.

Origins and History

OpenFaaS was created by Alex Ellis in December 2016, initially as a proof of concept for running serverless functions on Docker Swarm. The project was open-sourced in 2017 and quickly gained popularity, accumulating over 25,000 GitHub stars. OpenFaaS is licensed under the MIT License (Community Edition). Ellis founded OpenFaaS Ltd to provide commercial support and the Pro edition. The project later added full Kubernetes support via the faas-netes provider, which became the primary deployment target.

Sources

  1. https://www.openfaas.com/
  2. https://github.com/openfaas/faas