High availability cluster setup in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a high availability (HA) cluster in Kubernetes?

A high availability cluster in Kubernetes is a setup where multiple master nodes run simultaneously to ensure the cluster remains operational even if one or more masters fail.

beginner

Why do we use multiple master nodes in an HA Kubernetes cluster?

Multiple master nodes provide redundancy. If one master node fails, others continue managing the cluster, preventing downtime.

intermediate

What role does etcd play in a Kubernetes HA cluster?

etcd stores the cluster's configuration and state data. In HA, etcd runs as a cluster itself to keep data consistent and available across master nodes.

intermediate

How does a load balancer contribute to a Kubernetes HA cluster?

A load balancer distributes requests to the multiple master nodes, ensuring traffic is balanced and the cluster remains reachable even if one master fails.

beginner

Name one common tool or method to set up a Kubernetes HA cluster.

Using kubeadm with multiple control plane nodes and an external load balancer is a common method to set up a Kubernetes HA cluster.

What is the main purpose of having multiple master nodes in a Kubernetes HA cluster?

A To speed up container image downloads

B To increase the number of worker nodes

C To reduce the number of pods running

D To provide redundancy and avoid single points of failure

Multiple master nodes ensure the cluster control plane stays available if one master fails.

Which component stores the cluster state in a Kubernetes HA setup?

A kubelet

B etcd

C kube-proxy

D container runtime

etcd is the key-value store that holds the cluster's state and configuration.

What is the role of a load balancer in a Kubernetes HA cluster?

A To distribute requests to multiple master nodes

B To balance traffic between worker nodes

C To store container images

D To monitor pod health

The load balancer directs API requests to available master nodes to maintain availability.

Which command-line tool is commonly used to initialize a Kubernetes HA cluster?

A kubectl

B docker

C kubeadm

D helm

kubeadm is used to bootstrap Kubernetes clusters, including HA setups.

In a Kubernetes HA cluster, what happens if one master node goes down?

A The cluster continues running using other master nodes

B All pods are deleted

C The entire cluster stops working

D Worker nodes shut down automatically

Other master nodes take over control to keep the cluster operational.

Explain the key components and their roles in a Kubernetes high availability cluster setup.

Think about how the cluster stays up if one part fails.

Describe the steps to set up a basic Kubernetes HA cluster using kubeadm.

Focus on the order and components involved.

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