The deployment of a Kubernetes cluster on Raspberry Pi hardware represents a convergence of low-power ARM64 computing and enterprise-grade container orchestration. By utilizing K3s, a lightweight, CNCF-certified Kubernetes distribution, users can transform a series of single-board computers into a resilient, distributed system capable of running production workloads, IoT edge services, or personal development environments. Unlike standard Kubernetes distributions (K8s), which are often resource-heavy and designed for massive data center nodes, K3s is specifically engineered for resource-constrained environments. When coupled with the Rancher management platform, the complexity of managing a distributed cluster—including node registration, workload distribution, and visibility—is significantly reduced. This architecture allows for the implementation of high-availability (HA) patterns, where a control plane manages multiple worker nodes, ensuring that the failure of a single Raspberry Pi does not result in the catastrophic failure of the entire service ecosystem.
Architectural Components and Hardware Requirements
The foundation of a Raspberry Pi Kubernetes cluster relies on the strategic selection of hardware and the accompanying software stack. While K3s can technically run on a single instance, the establishment of a base level of resiliency requires at least three Raspberry Pi units. This configuration typically consists of one primary node serving as the control plane (running the K3s server) and at least two secondary nodes acting as worker nodes (running the K3s agent).
The hardware versatility of the platform is significant. While modern guides leverage the enhanced processing power and I/O capabilities of the Raspberry Pi 5, the ecosystem remains compatible with various ARM64 Raspberry Pi models. For example, setups utilizing Raspberry Pi 4 with 4GB of memory provide a stable environment for mid-sized hobby projects. In high-density configurations, the use of PoE (Power over Ethernet) headers allows the nodes to be stacked and powered via a single PoE switch, eliminating the need for multiple individual power adapters and reducing cable clutter.
The software stack required for a fully functional, production-ready local cluster includes:
- Ubuntu Server 24.04.2 LTS: This 64-bit operating system provides the necessary kernel support and stability for ARM64 architectures.
- K3s (Version 1.31): The core Kubernetes distribution that replaces heavy components with lightweight alternatives.
- MetalLB: A network load balancer specifically designed for bare-metal clusters to handle external traffic.
- Nginx: Used as the ingress controller to manage how external requests reach internal services.
- Cert-manager: An automated certificate issuer to ensure secure HTTPS communication.
- Rancher: The overarching orchestration platform for visual management and lifecycle control.
The impact of these choices is a system that balances the limited thermal and power envelopes of the Raspberry Pi with the robust requirements of the Kubernetes API. Connecting these components creates a dense web of dependencies where the OS provides the runtime, K3s provides the orchestration, and Rancher provides the administrative interface.
Operating System Preparation and Node Initialization
Before the K3s installation process begins, the underlying operating system must be meticulously prepared. The primary requirement is the installation of a 64-bit OS, such as Ubuntu Server 24.04.2 LTS. This is a critical requirement because Kubernetes and K3s rely on 64-bit instructions to manage memory and process orchestration efficiently across the cluster.
The initialization process follows a strict sequence to ensure cluster stability:
- Flash the microSD cards: Each Raspberry Pi requires a microSD card flashed with the 64-bit Ubuntu Server image. High-capacity cards, such as 64GB Samsung SDXC, are recommended to accommodate the OS and the container image cache.
- Network Configuration: The control plane node must be assigned a static or reserved IP address. This prevents the worker nodes from losing connection to the server if the DHCP server reassigns the control plane's IP address.
- Hostname Assignment: Each node in the cluster must be given a unique hostname. Unique identifiers are necessary for the Kubernetes API to distinguish between nodes when scheduling pods and managing resources.
- Tool Installation: Helm, the package manager for Kubernetes, should be installed on the control plane using Snap. This allows the administrator to deploy complex applications and the aforementioned MetalLB or Nginx components using standardized charts.
For users who prefer an alternative to Ubuntu, RancherOS provides specialized images for Raspberry Pi. As of version 0.5.0, these images are available for download. However, it is noted that only Raspberry Pi 3 has been fully tested and confirmed to work with the official RancherOS images. Unlike traditional OS installations, RancherOS does not support cloud-config during the initial installation; users must boot the device, manually alter the configuration, and reboot to apply changes.
K3s Server and Agent Deployment
The deployment of K3s is divided into two distinct roles: the Server (Control Plane) and the Agent (Worker). The Server manages the cluster state, schedules pods, and handles the Kubernetes API. The Agent simply executes the workloads assigned by the server.
The installation of the server is typically initiated via a curl command that pulls the K3s installation script. Once the server is active, it generates a server token. This token is a critical security credential that must be exported and shared with worker nodes to allow them to join the cluster securely.
To install the agents on worker nodes, the following process is employed:
- Establish an SSH connection to the worker node (e.g.,
ssh pi2). - Export the server token as a variable:
export TOKEN=***REDACTED*** - Execute the K3s agent installation script:
curl -sfL https://get.k3s.io agent | INSTALL_K3S_EXEC="agent --server https://192.168.1.10:6443 --token $TOKEN" sh -
The use of the INSTALL_K3S_EXEC variable allows the agent to be told exactly where the server is located (using the static IP assigned to the control plane) and which token to use for authentication. This process can be executed individually on each node or broadcast to all worker nodes simultaneously via SSH to accelerate the deployment.
Once the agents are installed, the status of the cluster is verified using the kubectl command. Running kubectl get nodes will display the list of registered nodes and their current status (Ready/NotReady). This confirmation ensures that the worker nodes have successfully registered with the main node and are ready to receive pod assignments.
Advanced Storage and Network Configuration
A common limitation of Raspberry Pi clusters is the storage constraints of microSD cards. In RancherOS environments, the root partition does not automatically expand to fill the remainder of the SD card. To solve this, a workaround is used to store Docker containers on a larger, manually created partition.
The process for expanding storage for Docker includes the following technical steps:
- Partitioning: Use
sudo fdisk /dev/mmcblk0to create a new partition, accepting the defaults. - Writing and Rebooting: Write the partition table and execute
sudo reboot. - Directory Creation: Create a mount point using
sudo mkdir /mnt/docker. - Docker Configuration: Configure Docker to use the new root via
sudo ros config set rancher.docker.extra_args [-g,/mnt/docker]. - Formatting: Format the new partition using
sudo mkfs.ext4 /dev/mmcblk0p3. - Persistent Mounting: Preserve the mount across reboots with
sudo ros config set mounts "[['/dev/mmcblk0p3','/mnt/docker','ext4','']]". - Mounting: Execute
sudo mount /dev/mmcblk0p3 /mnt/docker. - Service Restart: Restart the Docker service using
sudo system-docker restart docker. - Data Migration: If existing data exists, it must be recursively copied using
sudo cp -R /var/lib/docker/* /mnt/dockerbefore restarting the service again.
In terms of networking, the transition from local cluster traffic to external internet access requires specific routing. For instance, in a setup using a Mikrotik RB4011 router with a LAN CIDR of 192.168.11.0/24, destination NAT (dst-nat) rules must be configured. The IP address 192.168.11.50 is typically designated as the Loadbalancer IP, which acts as the entry point for external users reaching the Kubernetes services.
Furthermore, for nodes that cannot be connected via Ethernet, Wi-Fi can be enabled in RancherOS (v1.5.2 and later) using the following commands:
- Load the driver:
modprobe brcmfmac - Create the passphrase file:
wpa_passphrase <ssid> <psk> > /etc/wpa_supplicant.conf - Start the supplicant:
wpa_supplicant -iwlan0 -B -c /etc/wpa_supplicant.conf - Request an IP:
dhcpcd -MA4 wlan0
Alternatively, Wi-Fi can be configured via a #cloud-config file by specifying the wifi_network and ssid under the rancher.network.interfaces.wlan0 section.
Comparative Analysis of Cluster Specifications
The following table summarizes the hardware and software specifications across different Raspberry Pi cluster implementations described in the reference materials.
| Component | Standard K3s Cluster (Pi 5) | Hobbyist Cluster (Pi 4) | RancherOS Cluster (Pi 3) |
|---|---|---|---|
| OS | Ubuntu Server 24.04.2 LTS (64-bit) | Ubuntu 20.04 | RancherOS (v0.5.0+) |
| Kubernetes Distro | K3s (v1.31) | K3s | K3s/RancherOS |
| Node Count | 3+ Nodes | 3 Nodes | Varies |
| Memory (Typical) | Varies (ARM64) | 4GB per node | Varies |
| Storage | microSD Card | 64GB Samsung SDXC | microSD Card (Manual Expansion) |
| Network | Static IP / Reserved IP | PoE Switch / Mikrotik Router | Wi-Fi / Ethernet |
| Load Balancer | MetalLB | dst-nat Script (192.168.11.50) | Not Specified |
Technical Analysis of the K3s and Rancher Ecosystem
The synergy between K3s and Rancher creates a powerful abstraction layer for the end user. K3s achieves its lightweight profile by stripping out legacy cloud-provider code and replacing the etcd database with SQLite for single-node or small-cluster deployments, although it remains fully compatible with etcd for high-availability configurations. This reduction in footprint is what allows a Raspberry Pi with limited RAM to maintain a functional control plane without succumbing to Out-Of-Memory (OOM) kills.
From a DevOps perspective, the integration of Helm on the control plane enables a declarative approach to infrastructure. Instead of manually configuring ingress and load balancing, the administrator can deploy the MetalLB and Nginx pods using Helm charts, ensuring that the network configuration is reproducible and version-controlled.
The real-world impact of this architecture is evident in the ability to host services such as Ghost servers or other containerized blogs. By deploying a bare-metal cluster, the user avoids the costs associated with cloud providers while gaining experience in managing pod scheduling, node affinity, and network ingress. The risk of hardware failure is mitigated by the 3-node minimum recommendation; if one worker node fails, Kubernetes automatically redistributes the pods to the remaining healthy nodes, provided the cluster has sufficient resource headroom.
The use of the curl -sfL https://get.k3s.io installation method is a testament to the "simplicity first" philosophy of K3s. By automating the binary download and service configuration, the barrier to entry for "noobs" and tech enthusiasts is lowered, while the underlying system remains a certified Kubernetes distribution suitable for production IoT workloads.
Conclusion
The deployment of K3s on Raspberry Pi hardware constitutes a sophisticated balance between resource constraints and operational power. By leveraging a 64-bit OS like Ubuntu Server 24.04.2 LTS and utilizing the streamlined installation process of K3s, users can establish a functional Kubernetes environment that mirrors enterprise architectures. The critical nature of static IP assignment for the control plane and the use of unique hostnames ensures that the cluster maintains a stable identity within the local network. Furthermore, the implementation of MetalLB and Nginx provides the necessary networking infrastructure to transform a local experiment into a reachable service.
The analysis of storage limitations reveals that while microSD cards are the primary medium, the manual partitioning of the SD card in RancherOS environments is essential for maintaining a healthy Docker root. This prevents the root partition from becoming a bottleneck for container image storage. The ability to integrate this hardware into a larger management framework via Rancher allows for a centralized view of the cluster's health, resource consumption, and workload distribution.
Ultimately, the transition from a single Raspberry Pi to a multi-node K3s cluster transforms the device from a simple computer into a distributed system. Whether used for hobbyist projects, such as hosting a Ghost blog, or for testing microservices architecture, the combination of Raspberry Pi and K3s provides a scalable, low-cost entry point into the world of cloud-native computing. The resilience provided by a 3-node setup, combined with the automation of Helm and the visibility of Rancher, ensures that the cluster is not only a learning tool but a viable production environment for edge computing.