How to Set Up a High Availability (HA) Kubernetes Cluster with Kubeadm

Kubernetes (k8s) is a powerful orchestration tool that allows you to manage containerized applications across a cluster of nodes. Setting up a High Availability (HA) Kubernetes cluster ensures that your applications remain available even if one or more nodes fail. This comprehensive guide will walk you through the process of setting up a HA Kubernetes cluster using Kubeadm.

Table of Contents

1. Introduction
2. Prerequisites
3. Step 1: Prepare Your Environment
4. Step 2: Install Docker on All Nodes
5. Step 3: Install Kubernetes Components on All Nodes
6. Step 4: Set Up HAProxy and Keepalived
7. Step 5: Initialize the Kubernetes Control Plane
8. Step 6: Join Worker Nodes to the Cluster
9. Step 7: Verify the Cluster
10. Conclusion

Introduction

Setting up a HA Kubernetes cluster with Kubeadm involves configuring multiple control plane nodes, ensuring that the cluster can withstand the failure of one or more control planes. This guide provides step-by-step instructions to help you achieve a robust and resilient Kubernetes setup.

Prerequisites

Before you start, ensure you have the following:

• At least three machines (virtual or physical) running a supported version of Linux (e.g., Ubuntu 20.04).
• At least 2GB of RAM and 2 CPUs per machine.
• A user account with sudo privileges on all machines.
• Internet access for downloading packages and images.

Step 1: Prepare Your Environment

First, update and upgrade all your nodes:

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sudo apt update sudo apt upgrade -y

Disable swap on all nodes:

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sudo swapoff -a sudo sed -i '/ swap / s/^/#/' /etc/fstab

Enable required kernel modules and configure sysctl:

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sudo modprobe overlay sudo modprobe br_netfilter cat <<EOF | sudo tee /etc/sysctl.d/k8s.conf net.bridge.bridge-nf-call-iptables = 1 net.bridge.bridge-nf-call-ip6tables = 1 net.ipv4.ip_forward = 1 EOF sudo sysctl --system

Step 2: Install Docker on All Nodes

Install Docker, which Kubernetes uses as the default container runtime:

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sudo apt update sudo apt install -y apt-transport-https ca-certificates curl software-properties-common curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add - sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" sudo apt update sudo apt install -y docker-ce sudo systemctl enable docker sudo systemctl start docker

Step 3: Install Kubernetes Components on All Nodes

Install kubeadm, kubelet, and kubectl:

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sudo apt update sudo apt install -y apt-transport-https ca-certificates curl curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add - sudo add-apt-repository "deb http://apt.kubernetes.io/ kubernetes-xenial main" sudo apt update sudo apt install -y kubelet kubeadm kubectl sudo apt-mark hold kubelet kubeadm kubectl

Step 4: Set Up HAProxy and Keepalived

To ensure high availability of the control plane, set up HAProxy and Keepalived on a load balancer node.

Install HAProxy:

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sudo apt install -y haproxy

Configure HAProxy to load balance traffic to the Kubernetes API servers. Edit /etc/haproxy/haproxy.cfg:

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frontend kubernetes-frontend    bind *:6443    option tcplog    mode tcp    default_backend kubernetes-backend backend kubernetes-backend    mode tcp    balance roundrobin    server master1 <Master1_IP>:6443 check    server master2 <Master2_IP>:6443 check    server master3 <Master3_IP>:6443 check

Restart HAProxy:

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sudo systemctl restart haproxy

Install Keepalived:

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sudo apt install -y keepalived

Configure Keepalived for VIP (Virtual IP):

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cat <<EOF | sudo tee /etc/keepalived/keepalived.conf vrrp_instance VI_1 {    state MASTER    interface <network_interface>    virtual_router_id 51    priority 100    authentication {        auth_type PASS        auth_pass <password>    }    virtual_ipaddress {        <Virtual_IP>    } } EOF

Start Keepalived:

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sudo systemctl enable keepalived sudo systemctl start keepalived

Step 5: Initialize the Kubernetes Control Plane

On the first control plane node, initialize the cluster using kubeadm:

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sudo kubeadm init --control-plane-endpoint "<Virtual_IP>:6443" --upload-certs

Save the join command with the certificate key provided in the output. It will be used to join additional control plane nodes.

Set up your local kubectl configuration:

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mkdir -p $HOME/.kube sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config sudo chown $(id -u):$(id -g) $HOME/.kube/config

Install the CNI (Container Network Interface) plugin, for example, Calico:

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kubectl apply -f https://docs.projectcalico.org/v3.14/manifests/calico.yaml

Step 6: Join Worker Nodes to the Cluster

Use the join command from the kubeadm init output to join the worker nodes to the cluster:

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sudo kubeadm join <Virtual_IP>:6443 --token <token> --discovery-token-ca-cert-hash sha256:<hash>

Step 7: Verify the Cluster

Ensure all nodes are joined and ready:

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kubectl get nodes

You should see all control plane and worker nodes listed with the status Ready.

Conclusion

Setting up a HA Kubernetes cluster with Kubeadm ensures your applications remain resilient and available. This guide provided step-by-step instructions to achieve a robust and scalable Kubernetes environment.

Compelling Summary: Setting up a HA Kubernetes cluster with Kubeadm ensures robust, resilient application management, offering a reliable environment even during failures.

References

• Kubernetes Official Documentation
• Kubeadm Official Documentation
• HAProxy Documentation
• Keepalived Documentation

By following these steps, you will have a fully functional and highly available Kubernetes cluster capable of handling production workloads.