High availability cluster setup in Kubernetes - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the number of master nodes in a Kubernetes HA cluster.

Kubernetes

apiVersion: kubeadm.k8s.io/v1beta3
kind: ClusterConfiguration
controlPlaneEndpoint: "loadbalancer.example.com:6443"
controllerManager:
  extraArgs:
    node-monitor-grace-period: "40s"
    node-monitor-period: "5s"
    pod-eviction-timeout: "1m0s"
scheduler:
  extraArgs:
    leader-elect: "true"
---
apiVersion: kubeadm.k8s.io/v1beta3
kind: InitConfiguration
nodeRegistration:
  name: master-1
  kubeletExtraArgs:
    node-labels: "node-role.kubernetes.io/master="
    authorization-mode: AlwaysAllow
---
apiVersion: kubeadm.k8s.io/v1beta3
kind: JoinConfiguration
controlPlane:
  localAPIEndpoint:
    advertiseAddress: "192.168.1.10"
    bindPort: 6443
  [1]: 3

Drag options to blanks, or click blank then click option'

AmasterCount

BreplicaCount

CcontrolPlaneReplicas

Dreplicas

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'replicaCount' which is common in Helm charts but not in kubeadm config.

Using 'masterCount' which is not a valid kubeadm key.

The correct key to specify the number of master nodes in kubeadm HA setup is 'replicas'.

2fill in blank

medium

Complete the command to initialize the Kubernetes control plane with high availability.

Kubernetes

kubeadm init --control-plane-endpoint [1] --upload-certs

Drag options to blanks, or click blank then click option'

A192.168.1.10:6443

Bloadbalancer.example.com:6443

Cmaster-1:6443

Dlocalhost:6443

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single master node IP instead of the load balancer.

Using localhost which is not accessible externally.

The control plane endpoint should be the load balancer address that fronts the master nodes.

3fill in blank

hard

Fix the error in the kubeadm join command to add a new control plane node.

Kubernetes

kubeadm join loadbalancer.example.com:6443 --token [1] --discovery-token-ca-cert-hash sha256:abcdef1234567890 --control-plane --certificate-key abcdef1234567890

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A0123456789abcdef

Babcdef

Cabcdef.0123456789abcdef

Dtoken1234

Attempts:

3 left

💡 Hint

Common Mistakes

Using incomplete or partial token strings.

Omitting the dot separator in the token.

The token must be in the correct format with a dot separating two parts, e.g., 'abcdef.0123456789abcdef'.

4fill in blank

hard

Fill both blanks to create a Kubernetes Service manifest for the HA control plane load balancer.

Kubernetes

apiVersion: v1
kind: Service
metadata:
  name: kubernetes
  namespace: default
spec:
  type: [1]
  ports:
  - port: 6443
    targetPort: 6443
  selector:
    [2]: master-node

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ALoadBalancer

BClusterIP

Capp

Drole

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ClusterIP' which does not expose the service externally.

Using incorrect selector keys like 'app' when 'role' is expected.

The service type for external load balancing is 'LoadBalancer', and the selector key is commonly 'role' to select master nodes.

5fill in blank

hard

Fill all three blanks to define a Pod Anti-Affinity rule to spread master nodes across failure domains.

Kubernetes

affinity:
  podAntiAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
    - labelSelector:
        matchExpressions:
        - key: [1]
          operator: In
          values:
          - master
      topologyKey: [2]
  nodeAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
      nodeSelectorTerms:
      - matchExpressions:
        - key: [3]
          operator: In
          values:
          - zone-a
          - zone-b

Drag options to blanks, or click blank then click option'

Akubernetes.io/role

Bkubernetes.io/hostname

Cfailure-domain.beta.kubernetes.io/zone

Dnode-role.kubernetes.io/master

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect label keys for roles or topology.

Confusing node labels with pod labels.

The podAntiAffinity key is 'node-role.kubernetes.io/master', topologyKey is 'kubernetes.io/hostname' to spread pods across nodes, and nodeAffinity key is the zone label 'failure-domain.beta.kubernetes.io/zone'.

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