# K3s — Lightweight Certified Kubernetes Distribution

> K3s is a fully compliant, lightweight Kubernetes distribution that runs in less than 512MB RAM. Perfect for edge, IoT, ARM, CI/CD, and resource-constrained environments.

## Install

Save in your project root:

## Quick Use

```bash
# Install on any Linux (takes 30 seconds)
curl -sfL https://get.k3s.io | sh -

# Check status
sudo k3s kubectl get nodes

# Run a workload
sudo k3s kubectl create deployment nginx --image=nginx
sudo k3s kubectl expose deployment nginx --port=80 --type=NodePort
```

## Intro

**K3s** is a fully compliant Kubernetes distribution designed for resource-constrained environments. Built by Rancher Labs (now SUSE), it packages Kubernetes into a single binary under 100MB that uses less than 512MB of RAM, making it perfect for edge computing, IoT devices, CI/CD pipelines, and developers who want Kubernetes without the operational complexity.

With 32.7K+ GitHub stars and Apache-2.0 license, K3s is the most popular lightweight Kubernetes distribution, certified by the CNCF and used in production from home labs to large enterprises.

## What K3s Does

- **Single Binary**: Everything (API server, scheduler, kubelet, etc.) in one <100MB binary
- **Low Resource**: Runs Kubernetes in <512MB RAM (minimum)
- **Easy Install**: One curl command to install a complete cluster
- **SQLite or etcd**: Lightweight SQLite backend by default, embedded etcd for HA
- **Built-in**: Traefik ingress, Flannel CNI, CoreDNS, local-path storage, metrics-server
- **ARM Support**: Runs on Raspberry Pi and other ARM devices
- **Air-Gap Ready**: Install without internet connection
- **High Availability**: HA cluster with embedded etcd (3+ server nodes)
- **Upgrade**: Simple version upgrades with automatic migration

## Architecture

```
┌─────────────────────────────────────┐
│       K3s Single Binary              │
│  ┌──────────┐  ┌──────────────┐     │
│  │API Server│  │  Scheduler   │     │
│  └──────────┘  └──────────────┘     │
│  ┌──────────┐  ┌──────────────┐     │
│  │Controller│  │   Kubelet    │     │
│  │  Manager │  │              │     │
│  └──────────┘  └──────────────┘     │
│  ┌──────────┐  ┌──────────────┐     │
│  │  Kine    │  │  Containerd  │     │
│  │ (SQLite) │  │              │     │
│  └──────────┘  └──────────────┘     │
└─────────────────────────────────────┘
```

K3s replaces etcd with Kine (an abstraction layer), which can use SQLite, PostgreSQL, MySQL, or embedded etcd.

## Installation

### Single Node (Dev/Test)

```bash
# Install server (master)
curl -sfL https://get.k3s.io | sh -

# Kubeconfig is at /etc/rancher/k3s/k3s.yaml
sudo chmod 644 /etc/rancher/k3s/k3s.yaml
export KUBECONFIG=/etc/rancher/k3s/k3s.yaml

kubectl get nodes
```

### Multi-Node Cluster

```bash
# On the server (master) node
curl -sfL https://get.k3s.io | sh -
sudo cat /var/lib/rancher/k3s/server/node-token
# Save this token!

# On worker nodes
curl -sfL https://get.k3s.io | K3S_URL=https://server-ip:6443 K3S_TOKEN=your-token sh -
```

### High Availability (3 servers with embedded etcd)

```bash
# First server
curl -sfL https://get.k3s.io | sh -s - server 
  --cluster-init 
  --token=shared-secret

# Additional servers
curl -sfL https://get.k3s.io | sh -s - server 
  --server https://first-server:6443 
  --token=shared-secret
```

### Uninstall

```bash
# On server
/usr/local/bin/k3s-uninstall.sh

# On agent
/usr/local/bin/k3s-agent-uninstall.sh
```

## Key Features

### Built-in Components

K3s includes batteries-included components you'd otherwise need to install separately:

```
├── Traefik (v2)         — Ingress controller
├── Flannel             — CNI networking
├── CoreDNS             — DNS service
├── Metrics Server      — kubectl top support
├── Local Path Provisioner — Default storage
├── Helm Controller     — HelmChart CRD support
└── Klipper LoadBalancer — ServiceType=LoadBalancer
```

Disable any component if you want to use alternatives:
```bash
curl -sfL https://get.k3s.io | sh -s - 
  --disable traefik 
  --disable servicelb
```

### Using with Rancher

```yaml
# Deploy Rancher management UI on K3s
kubectl create namespace cattle-system
kubectl apply -f https://github.com/cert-manager/cert-manager/releases/latest/download/cert-manager.yaml

helm repo add rancher-stable https://releases.rancher.com/server-charts/stable
helm install rancher rancher-stable/rancher 
  --namespace cattle-system 
  --set hostname=rancher.yourdomain.com
```

### Deploy Helm Charts

```yaml
# K3s natively supports HelmChart CRD
apiVersion: helm.cattle.io/v1
kind: HelmChart
metadata:
  name: grafana
  namespace: kube-system
spec:
  chart: grafana
  repo: https://grafana.github.io/helm-charts
  targetNamespace: monitoring
  valuesContent: |-
    service:
      type: LoadBalancer
    adminPassword: your-password
```

### Air-Gap Installation

```bash
# Download K3s binary and images
wget https://github.com/k3s-io/k3s/releases/download/v1.28.0%2Bk3s1/k3s
wget https://github.com/k3s-io/k3s/releases/download/v1.28.0%2Bk3s1/k3s-airgap-images-amd64.tar.gz

# On target machine
sudo mkdir -p /var/lib/rancher/k3s/agent/images/
sudo cp k3s-airgap-images-amd64.tar.gz /var/lib/rancher/k3s/agent/images/
sudo cp k3s /usr/local/bin/
sudo chmod +x /usr/local/bin/k3s
```

## Use Cases

| Scenario | Why K3s? |
|----------|----------|
| Edge computing | Low resource, ARM support |
| IoT devices | Raspberry Pi compatible |
| CI/CD pipelines | Fast startup, single binary |
| Developer workstation | Full K8s, low overhead |
| Home lab | Easy install, full featured |
| Branch offices | Air-gap ready |
| GitOps (Flux/ArgoCD) | HelmChart CRD support |

## K3s vs Alternatives

| Feature | K3s | K8s (kubeadm) | K0s | MicroK8s |
|---------|-----|---------------|-----|----------|
| Binary size | ~100MB | ~1GB+ | ~180MB | ~200MB |
| RAM (idle) | 512MB | 2GB+ | 500MB | 600MB |
| Install time | 30s | 30+ min | 30s | 60s |
| Backend | SQLite/etcd | etcd | etcd | dqlite |
| Certification | CNCF certified | Native | CNCF certified | CNCF certified |
| Best for | Edge, dev, prod | Prod at scale | Prod, edge | Ubuntu users |

## 常见问题

**Q: K3s 和完整 Kubernetes 功能相同吗？**
A: 是的。K3s 是 CNCF 认证的 Kubernetes 发行版，通过了所有一致性测试。差异只是打包方式——K3s 更小、更容易部署，但运行的是同样的 Kubernetes。

**Q: 适合生产环境吗？**
A: 非常适合。许多公司在生产环境大规模使用 K3s。SUSE（Rancher 母公司）提供商业支持。HA 模式下（3+ 服务器节点）可以提供生产级可用性。

**Q: 和 Docker Swarm 怎么选？**
A: 如果你需要 Docker Swarm 的简单性，选 Docker Swarm。如果你需要 Kubernetes 生态（Helm、Operators、复杂工作负载），但又不想要完整 K8s 的复杂性，选 K3s。K3s 是更好的长期选择。

## 来源与致谢

- GitHub: [k3s-io/k3s](https://github.com/k3s-io/k3s) — 32.7K+ ⭐ | Apache-2.0
- 官网: [k3s.io](https://k3s.io)

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Source: https://tokrepo.com/en/workflows/300fbdf6-3535-11f1-9bc6-00163e2b0d79
Author: AI Open Source