OpenFaaS — Serverless Functions Made Simple

Introduction

OpenFaaS turns any container into a function with a uniform HTTP interface and scale-to-zero behavior. It is the most popular open-source FaaS platform and runs on anything that speaks the Kubernetes or containerd APIs — including Raspberry Pi clusters.

What OpenFaaS Does

• Packages handlers as OCI images with a minimal watchdog process
• Exposes functions behind a single gateway with auth and metrics
• Autoscales via Prometheus alerts or HPA v2
• Supports async invocations through NATS JetStream
• Ships templates for Python, Node, Go, Ruby, Rust, PHP, Java and more

Architecture Overview

A gateway service (Go) routes HTTP requests to per-function Deployments; each function pod runs a watchdog that forks the handler or proxies HTTP. Metrics flow to Prometheus, which triggers scaling decisions. An optional queue-worker pulls async jobs from NATS and invokes functions with retries.

Self-Hosting & Configuration

• arkade install openfaas or the openfaas Helm chart
• faasd variant runs on a single VM via containerd (no K8s needed)
• Use OPENFAAS_URL and basic-auth/OIDC for the gateway
• Define functions in a stack.yml — faas-cli up builds, pushes, deploys
• Wire Prometheus + Grafana dashboards shipped with the chart

Key Features

• True scale-to-zero with configurable idle timeout
• Async invocations with NATS-backed retries and callbacks
• Function templates store and of-watchdog streaming handlers
• Works on ARM64 — great for edge and homelab
• Pro version adds multi-tenancy, CRDs and single sign-on

Comparison with Similar Tools

• Knative Serving — heavier, tied to Kubernetes and Istio/Contour
• Fission — similar idea, pool-based cold starts, less active
• AWS Lambda — managed only, provider lock-in
• Kubeless — archived
• Nuclio — data-science focused, richer triggers

FAQ

Q: Do I need Kubernetes? A: No — faasd runs the core stack on one VM with systemd + containerd.

Q: How do cold starts compare to Lambda? A: Warm pods are sub-10 ms; cold starts depend on image pull and usually land at 1–3 s.

Q: Can I use my own container image? A: Yes — set image: and fprocess: in stack.yml and skip the template.

Q: Is OpenFaaS CE still open source? A: Yes, MIT licensed; OpenFaaS Pro adds commercial features under EULA.

Sources

• https://github.com/openfaas/faas
• https://docs.openfaas.com/