OpenFaaS is a Functions-as-a-Service framework that runs on Kubernetes (via faas-netes) or directly on containerd (via faasd for single-node installs). A function is a container image that implements a simple HTTP watchdog contract: the of-watchdog sidecar binary receives requests, invokes your handler over stdin/stdout or HTTP, and returns the response, so any language or binary can become a function.
The control plane is an API gateway that fronts the function pods and exposes a REST API plus a CLI (faas-cli). Functions are defined in a stack.yaml that points at a language template, built with BuildKit, pushed to a registry, and deployed as Kubernetes Deployments. Autoscaling is driven by Prometheus metrics and handled either by OpenFaaS’s built-in scaler or by KEDA for event-driven scale-to-zero. Event connectors exist for Kafka, NATS, SQS, Postgres, cron, and MQTT, which turn OpenFaaS into a general-purpose event router rather than just an HTTP function runner.
Licensing is mixed: faas-netes, faasd, and the community templates are MIT, while OpenFaaS Pro and OpenFaaS Edge (features like HA, retries, long-running async jobs, SSO) are commercial under a EULA. In the cloud-native serverless space it competes with Knative Serving, Fission, Nuclio, OpenFunction, and Kubeless (archived). OpenFaaS’s niche is the classic container-per-function FaaS model with minimal moving parts.