High availability cluster setup in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Kubernetes Control Plane High Availability

Which component is not typically replicated to achieve high availability in a Kubernetes control plane setup?

A Controller Manager

B kubelet

C API Server

D etcd

💡 Hint

Think about which component runs on worker nodes rather than control plane nodes.

The kubelet runs on worker nodes and is not part of the control plane replication. The API Server, etcd, and Controller Manager are control plane components that are replicated for high availability.

💻 Command Output

intermediate

Check etcd Cluster Health in HA Setup

You run the command etcdctl endpoint health on a 3-node etcd cluster. What output indicates all nodes are healthy?

Kubernetes

etcdctl endpoint health

A endpoint https://10.0.0.1:2379 is healthy: successfully committed proposal

B endpoint https://10.0.0.1:2379 is unhealthy: failed to connect

C error: no endpoints found

D endpoint https://10.0.0.1:2379 is healthy: failed to commit proposal

💡 Hint

Healthy means the node successfully processes requests.

The message 'successfully committed proposal' means the etcd node is healthy and responding correctly.

❓ Configuration

advanced

Load Balancer Configuration for HA Kubernetes API Servers

Which load balancer configuration snippet correctly balances traffic to three Kubernetes API servers on port 6443?

A

frontend kubernetes-frontend
  bind *:6443
  default_backend kubernetes-backend
backend kubernetes-backend
  server master1 10.0.0.1:6443
  server master2 10.0.0.2:6443
  server master3 10.0.0.3:6443

B

frontend kubernetes-frontend
  bind *:6443
  default_backend kubernetes-backend
backend kubernetes-backend
  server master1 10.0.0.1:8080 check
  server master2 10.0.0.2:8080 check
  server master3 10.0.0.3:8080 check

C

frontend kubernetes-frontend
  bind *:6443
  default_backend kubernetes-backend
backend kubernetes-backend
  server master1 10.0.0.1:6443 check
  server master2 10.0.0.2:6443 check
  server master3 10.0.0.3:6443 check

D

frontend kubernetes-frontend
  bind *:6443
  default_backend kubernetes-backend
backend kubernetes-backend
  server master1 10.0.0.1:6443 check
  server master2 10.0.0.2:6443
  server master3 10.0.0.3:6443 check

💡 Hint

Health checks help detect unhealthy API servers.

Option C includes health checks on all servers, which is essential for load balancers to route traffic only to healthy API servers.

❓ Troubleshoot

advanced

Diagnosing Kubernetes API Server Failover Issue

In a 3-master HA Kubernetes cluster, the API server on master2 is down. The load balancer still sends traffic to master2, causing failures. What is the most likely cause?

A The load balancer does not have health checks configured for master2

B etcd cluster is unhealthy

C kubelet on master2 is not running

D Controller Manager is not running on master2

💡 Hint

Focus on how the load balancer detects server health.

If the load balancer lacks health checks, it will continue sending traffic to a down API server, causing failures.

🔀 Workflow

expert

Steps to Add a New Master Node to an Existing HA Kubernetes Cluster

What is the correct order of steps to add a new master node to an existing high availability Kubernetes cluster?

A 2,1,3,4

B 1,3,2,4

C 1,2,4,3

D 1,2,3,4

💡 Hint

Think about the dependencies: components must be installed before joining clusters, and load balancer updated last.

First install components, then join etcd, then join control plane, finally update load balancer to route traffic to the new master.

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