# Fission — Fast Serverless Functions on Kubernetes

> Fission is an open-source serverless framework for Kubernetes that lets developers deploy functions in Python, Go, Node.js, and other languages with sub-second cold starts and no container builds required.

## Install

Save in your project root:

# Fission — Fast Serverless Functions on Kubernetes

## Quick Use
```bash
# Install Fission CLI
curl -Lo fission https://github.com/fission/fission/releases/latest/download/fission-cli-linux
chmod +x fission && sudo mv fission /usr/local/bin/
# Install on existing K8s cluster
kubectl create -k "github.com/fission/fission/crds/v1?ref=v1.20.5"
helm install fission fission-charts/fission-all --namespace fission --create-namespace
# Deploy a function
fission env create --name python --image fission/python-env
fission fn create --name hello --env python --code hello.py
fission route create --method GET --url /hello --function hello
curl http://$FISSION_ROUTER/hello
```

## Introduction
Fission brings serverless functions to any Kubernetes cluster without vendor lock-in. Developers write functions in their preferred language, and Fission handles packaging, routing, scaling, and lifecycle management with minimal cold-start latency.

## What Fission Does
- Deploys functions from source code directly, no Dockerfile or container build step needed
- Maintains pre-warmed environment pools for sub-second cold starts
- Automatically scales functions from zero to thousands of instances based on demand
- Provides HTTP triggers, message queue triggers (Kafka, NATS), and timer triggers
- Supports canary deployments with traffic splitting for safe function rollouts

## Architecture Overview
Fission runs three core components on Kubernetes: the Controller (API server), the Router (HTTP gateway), and the Executor (manages function pods). The Executor uses a pool-based strategy that keeps warm containers ready, or a new-deploy strategy for heavier workloads. Functions are injected into pre-built environment containers at invocation time.

## Self-Hosting & Configuration
- Requires an existing Kubernetes cluster (1.23+) with Helm 3 for installation
- Environment images for Python, Go, Node.js, Java, Ruby, and .NET are provided officially
- Persistent storage for function source and build artifacts uses Kubernetes PVCs
- Prometheus and OpenTelemetry integrations are available for metrics and tracing
- Istio integration enables advanced traffic management and mTLS between functions

## Key Features
- Pool-based executor pre-warms containers for sub-second cold starts
- Multi-language support with pluggable environment images
- Built-in Kafka and NATS connectors for event-driven architectures
- Canary deployments with percentage-based traffic splitting
- Composable workflows chain multiple functions into pipelines

## Comparison with Similar Tools
- **OpenFaaS** — Also runs on K8s but requires building container images; Fission deploys from source directly
- **Knative** — More general-purpose serving platform; Fission is purpose-built for functions with faster cold starts
- **Kubeless** — Archived project; Fission is actively maintained with regular releases
- **AWS Lambda** — Vendor-locked SaaS; Fission runs on any Kubernetes cluster you control
- **Nuclio** — Strong on real-time data; Fission offers broader language support and simpler developer experience

## FAQ
**Q: How fast are Fission cold starts?**
A: With pool-based execution, cold starts are typically under 100ms since containers are pre-warmed and only the function code is loaded at invocation.

**Q: Can I use custom container images?**
A: Yes. You can build custom environment images or use the new-deploy executor strategy with your own Docker images.

**Q: Does Fission scale to zero?**
A: Yes. The new-deploy executor scales functions to zero replicas when idle and scales up on incoming requests.

**Q: What languages are supported?**
A: Official environments exist for Python, Go, Node.js, Java, Ruby, PHP, and .NET. Custom environments can be created for any language.

## Sources
- https://github.com/fission/fission
- https://fission.io/docs/

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Source: https://tokrepo.com/en/workflows/781fc161-39c9-11f1-9bc6-00163e2b0d79
Author: AI Open Source