# Virtual Kubelet — Run Kubernetes Pods on Serverless and External Backends

> Virtual Kubelet implements the Kubernetes kubelet interface as a pluggable provider, allowing pods to be scheduled onto serverless platforms, IoT edge nodes, or any non-traditional compute backend.

## Install

Save in your project root:

# Virtual Kubelet — Run Kubernetes Pods on Serverless and External Backends

## Quick Use
```bash
# Clone and build
git clone https://github.com/virtual-kubelet/virtual-kubelet.git
cd virtual-kubelet
make build

# Run with the mock provider for testing
export KUBECONFIG=~/.kube/config
./bin/virtual-kubelet --provider mock --nodename vk-mock
# A new node "vk-mock" appears in kubectl get nodes
```

## Introduction
Virtual Kubelet masquerades as a regular Kubernetes node by implementing the kubelet API. Instead of running containers on a real host, it delegates pod execution to an external provider — Azure Container Instances, AWS Fargate, HashiCorp Nomad, or custom backends. This lets clusters burst into serverless capacity or integrate with non-Kubernetes infrastructure.

## What Virtual Kubelet Does
- Registers as a node in the Kubernetes cluster and accepts pod scheduling
- Delegates pod lifecycle management (create, update, delete) to a pluggable provider
- Reports pod status, resource capacity, and node conditions back to the API server
- Enables transparent cluster bursting to serverless platforms for peak workloads
- Supports custom providers for IoT, edge computing, and batch job backends

## Architecture Overview
Virtual Kubelet runs a single Go binary that implements the Kubelet gRPC API. The core library handles node registration, lease renewal, and pod status synchronization with the Kubernetes API server. Provider implementations satisfy a Go interface (CreatePod, GetPod, DeletePod, GetPodStatus) and translate Kubernetes pod specs into the target platform's execution model. Taints and tolerations ensure only intended workloads land on the virtual node.

## Self-Hosting & Configuration
- Build from source or use provider-specific container images (e.g., Azure ACI provider, AWS Fargate provider)
- Requires a valid kubeconfig with permissions to register nodes and manage pods
- Configure node taints to prevent accidental scheduling of non-burst workloads
- Provider-specific settings (cloud credentials, region, resource limits) are passed via environment variables or config files
- Node capacity is reported to the scheduler by the provider (often set to large values for serverless backends)

## Key Features
- CNCF Sandbox project with a well-defined provider interface for custom backends
- Transparent to the Kubernetes scheduler: pods are scheduled using standard affinity, tolerations, and resource requests
- Providers exist for Azure Container Instances, AWS Fargate, Nomad, Alibaba ECI, and more
- Node-level resource metrics reported back to the cluster for HPA and monitoring integration
- Mock provider included for development, testing, and CI validation

## Comparison with Similar Tools
- **Karpenter** — Provisions real nodes on demand; Virtual Kubelet provisions virtual nodes backed by external compute
- **Kubernetes Cluster Autoscaler** — Scales node groups; does not integrate non-Kubernetes backends
- **KubeVirt** — Runs VMs as pods on real nodes; Virtual Kubelet delegates pods off-cluster
- **KubeEdge** — Extends Kubernetes to edge devices with a real agent; Virtual Kubelet abstracts away the agent entirely
- **Admiralty** — Multi-cluster scheduling via proxy pods; similar concept but focused on cluster federation

## FAQ
**Q: Does Virtual Kubelet run actual containers on the host?**
A: No. It acts as a proxy. The actual execution happens on the external platform defined by the provider.

**Q: How do I prevent regular workloads from landing on the virtual node?**
A: Apply a taint (e.g., virtual-kubelet.io/provider=mock:NoSchedule) and add matching tolerations only to workloads intended for the virtual node.

**Q: Can I use Virtual Kubelet with Horizontal Pod Autoscaler?**
A: Yes. The provider reports pod and node metrics, and HPA scales pod replicas as usual. Pods scheduled on the virtual node burst into the external backend.

**Q: Which providers are production-ready?**
A: The Azure ACI provider is the most mature and widely used. AWS Fargate, Alibaba ECI, and HashiCorp Nomad providers are also available.

## Sources
- https://github.com/virtual-kubelet/virtual-kubelet
- https://virtual-kubelet.io/

---
Source: https://tokrepo.com/en/workflows/asset-90a1ff65
Author: AI Open Source