High availability cluster setup in Kubernetes - Mini Project: Build & Apply

High Availability Cluster Setup

📖 Scenario: You are working as a DevOps engineer tasked with setting up a high availability Kubernetes cluster. This cluster will ensure that your application stays online even if one of the master nodes fails.Think of it like having multiple backup generators at home. If one stops working, the others keep the lights on without interruption.

🎯 Goal: Build a simple Kubernetes cluster configuration with multiple master nodes for high availability. You will create the initial cluster configuration, add a control plane endpoint, configure multiple master nodes, and finally verify the cluster status.

📋 What You'll Learn

Create a basic Kubernetes cluster configuration file named kubeadm-config.yaml with a single master node.

Add a control plane endpoint to enable high availability.

Add two additional master nodes to the configuration.

Verify the cluster status using kubectl commands.

💡 Why This Matters

🌍 Real World

High availability clusters keep applications running without interruption even if some servers fail, which is critical for business continuity.

💼 Career

DevOps engineers often set up and maintain highly available Kubernetes clusters to ensure reliable application deployment and uptime.

1

Create initial cluster configuration

Create a file named kubeadm-config.yaml with the following content exactly: a ClusterConfiguration kind, Kubernetes version v1.26.0, and a single control plane endpoint set to "localhost:6443". Include one master node with the name master1 and IP 192.168.1.10 under nodes.

Kubernetes

# Create kubeadm-config.yaml with ClusterConfiguration, version v1.26.0, controlPlaneEndpoint localhost:6443, and one master node named master1 with IP 192.168.1.10
# Your code here

Hint

Use YAML format. The controlPlaneEndpoint is the address clients use to connect to the cluster.

2

Add control plane endpoint for high availability

Modify kubeadm-config.yaml to change the controlPlaneEndpoint from "localhost:6443" to "ha-cluster.example.com:6443" to enable high availability access point.

Kubernetes

apiVersion: kubeadm.k8s.io/v1beta3
kind: ClusterConfiguration
kubernetesVersion: v1.26.0
controlPlaneEndpoint: "localhost:6443"
nodes:
  - name: master1
    ip: 192.168.1.10
    role: master
# Change controlPlaneEndpoint to ha-cluster.example.com:6443
# Your code here

Hint

The controlPlaneEndpoint should be a DNS name or IP that points to your load balancer for masters.

3

Add two more master nodes

Add two more master nodes to kubeadm-config.yaml under nodes: master2 with IP 192.168.1.11 and master3 with IP 192.168.1.12. Both should have the role master.

Kubernetes

apiVersion: kubeadm.k8s.io/v1beta3
kind: ClusterConfiguration
kubernetesVersion: v1.26.0
controlPlaneEndpoint: "ha-cluster.example.com:6443"
nodes:
  - name: master1
    ip: 192.168.1.10
    role: master
# Add master2 and master3 nodes with their IPs and role master
# Your code here

Hint

Indent the new nodes properly under nodes in YAML.

4

Verify cluster status

Run the command kubectl get nodes to display the status of all nodes in the cluster.

Kubernetes

# Run kubectl get nodes to check cluster status
# Your code here

Hint

Make sure your cluster is running and kubectl is configured to connect to it.

Practice

1. What is the main purpose of setting up a high availability (HA) cluster in Kubernetes?

easy

A. To prevent downtime by having multiple master nodes

B. To reduce the number of worker nodes

C. To speed up pod creation on a single node

D. To disable load balancing between nodes

Solution

1. Step 1: Understand HA cluster purpose

   High availability clusters are designed to avoid downtime by having multiple master nodes so if one fails, others take over.

2. Step 2: Compare options

   Options B, C, and D do not relate to preventing downtime or multiple masters.

3. Final Answer:

   To prevent downtime by having multiple master nodes -> Option A

4. Quick Check:

   HA cluster = multiple masters for uptime [OK]

Hint: HA means multiple masters to avoid downtime [OK]

Common Mistakes:

• Thinking HA reduces worker nodes
• Confusing HA with pod scaling
• Ignoring the role of multiple masters

2. Which of the following is the correct syntax to initialize a Kubernetes HA cluster using kubeadm with a config file named ha-config.yaml?

easy

A. kubeadm create cluster ha-config.yaml

B. kubeadm start --config=ha-config.yaml

C. kubeadm init --config ha-config.yaml

D. kubeadm init ha-config.yaml

Solution

1. Step 1: Recall kubeadm init syntax

   The correct command to initialize a cluster with a config file is kubeadm init --config filename.

2. Step 2: Check options

   kubeadm init --config ha-config.yaml matches the correct syntax. Options A, B, and D use incorrect commands or missing flags.

3. Final Answer:

   kubeadm init --config ha-config.yaml -> Option C

4. Quick Check:

   kubeadm init + --config = correct syntax [OK]

Hint: Use 'kubeadm init --config filename' to start HA cluster [OK]

Common Mistakes:

• Using 'start' instead of 'init'
• Omitting '--config' flag
• Passing config file without flag

3. Given the following HA cluster setup snippet in ha-config.yaml:

apiVersion: kubeadm.k8s.io/v1beta3
kind: ClusterConfiguration
controlPlaneEndpoint: "lb.example.com:6443"
---
apiVersion: kubeproxy.config.k8s.io/v1alpha1
kind: KubeProxyConfiguration
mode: ipvs

What does the controlPlaneEndpoint specify in this configuration?

medium

A. The IP address of the worker node

B. The port for kubelet communication

C. The DNS name of the pod network

D. The load balancer address for master nodes

Solution

1. Step 1: Understand controlPlaneEndpoint role

   This field defines the address (usually a load balancer) that routes traffic to the master nodes in an HA setup.

2. Step 2: Analyze options

   The load balancer address for master nodes correctly identifies it as the load balancer address. Other options do not relate to controlPlaneEndpoint.

3. Final Answer:

   The load balancer address for master nodes -> Option D

4. Quick Check:

   controlPlaneEndpoint = load balancer address [OK]

Hint: controlPlaneEndpoint points to the HA load balancer [OK]

Common Mistakes:

• Confusing it with worker node IP
• Thinking it is pod network DNS
• Mixing it with kubelet port

4. You tried to join a new master node to your HA cluster using this command:

kubeadm join lb.example.com:6443 --token abcdef.0123456789abcdef --discovery-token-ca-cert-hash sha256:12345

But it failed with an error about missing --control-plane flag. What is the correct fix?

medium

A. Remove the token from the command

B. Add the --control-plane flag to the join command

C. Use kubeadm init instead of join

D. Change the port number to 8080

Solution

1. Step 1: Identify the error cause

   Joining a master node requires the --control-plane flag to indicate it is a control plane node.

2. Step 2: Apply the fix

   Add --control-plane to the join command to fix the error.

3. Final Answer:

   Add the --control-plane flag to the join command -> Option B

4. Quick Check:

   Joining master needs --control-plane flag [OK]

Hint: Joining master nodes requires --control-plane flag [OK]

Common Mistakes:

• Removing token breaks authentication
• Using init instead of join for adding nodes
• Changing port to wrong value

5. You want to set up a Kubernetes HA cluster with 3 master nodes behind a load balancer. Which of the following steps is the correct order to achieve this?

hard

A. Set up load balancer -> Initialize first master with kubeadm and config -> Join other masters with --control-plane -> Join worker nodes

B. Initialize all masters separately -> Set up load balancer -> Join worker nodes

C. Join worker nodes -> Initialize first master -> Set up load balancer -> Join other masters

D. Set up load balancer -> Join worker nodes -> Initialize all masters

Solution

1. Step 1: Set up load balancer first

   The load balancer must be ready to route traffic to masters before initializing the cluster.

2. Step 2: Initialize first master with kubeadm and config

   This creates the cluster control plane and configures the controlPlaneEndpoint.

3. Step 3: Join other masters with --control-plane flag

   Other masters join as control plane nodes to form HA.

4. Step 4: Join worker nodes

   Finally, worker nodes join the cluster to run workloads.

5. Final Answer:

   Set up load balancer -> Initialize first master with kubeadm and config -> Join other masters with --control-plane -> Join worker nodes -> Option A

6. Quick Check:

   Load balancer first, then masters, then workers [OK]

Hint: Load balancer first, then init masters, then join workers [OK]

Common Mistakes:

• Initializing all masters before load balancer
• Joining workers before masters
• Skipping --control-plane flag on masters