Introduction

By default, a Crusoe Managed Kubernetes (CMK) cluster is configured with a pod CIDR range of /16 and a node CIDR mask of /24. This setup allows for a total of 65,536 pod IP addresses. Since each node is allocated a /24 subnet (providing 256 IPs), the cluster can support a maximum of 256 nodes (65,536/256). This guide explains how users can create a CMK cluster that supports more than 256 nodes.

Prerequisites

Before starting, ensure you have the following:

• Access to a Crusoe Cloud project with appropriate permissions
• A CMK cluster with the latest image version (>= 1.30.8-cmk.26)
• Kubeconfig to access your CMK cluster
• Access to Crusoe CLI or Console 

Step-by-Step Instructions

To create a CMK cluster that supports more than 256 nodes, you need to specify a larger pod CIDR range and/or a smaller node CIDR mask during the cluster creation process.

Using Crusoe CLI

When creating a cluster using the Crusoe CLI, use the --cluster-cidr and --node-cidr-mask-size flags to define the desired network configuration.

Example:

To create a cluster named large-cluster with cluster version 1.30.8-cmk.26 in the eu-iceland1 location, with a pod CIDR range of 10.0.0.0/8 and a node CIDR mask size of /24, use the following command:

crusoe kubernetes clusters create --name large-cluster --cluster-version 1.30.8-cmk.26 --location eu-iceland1-a --cluster-cidr "10.0.0.0/8" --node-cidr-mask-size 24

Using Crusoe Cloud Console (UI)

When creating a cluster via the Crusoe Cloud Console, you will find options to configure the "Pod CIDR" and "Node Mask Size" during the cluster configuration steps. Modify these values according to your requirements.

Understanding CIDR Ranges and Node Capacity

The following table provides a reference for adjusting the Pod CIDR range and per-node CIDR mask to support your desired number of nodes and pods per node:

General Formula:

The number of nodes a cluster can support is determined by the total number of usable IP addresses available for pods divided by the number of usable IP addresses allocated to each node.

Number of Nodes = Usable IPs per Node / Total Usable IPs for Pods​

Where:

• Total Usable IPs for Pods is determined by the --cluster-cidr. A smaller CIDR suffix (e.g., /14) provides a larger range of IP addresses.
• Usable IPs per Node is determined by the --node-cidr-mask-size. A larger CIDR suffix (e.g., /24) provides fewer IP addresses per node, while a smaller suffix (e.g., /26) provides more.

Additional Resources

• Kubernetes Documentation