DNS in Kubernetes (CoreDNS) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check the CoreDNS pods in the kube-system namespace.

Kubernetes

kubectl get pods -n [1] -l k8s-app=kube-dns

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

Adns

Bdefault

Ccore-dns

Dkube-system

Attempts:

3 left

💡 Hint

Common Mistakes

Using the default namespace instead of kube-system

Using an incorrect label selector

The CoreDNS pods run in the kube-system namespace, so you must specify it to list them.

2fill in blank

medium

Complete the command to view the CoreDNS ConfigMap in the kube-system namespace.

Kubernetes

kubectl get configmap [1] -n kube-system -o yaml

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

Acoredns-config

Bcoredns

Cdns-config

Dcore-dns-configmap

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect ConfigMap names like coredns-config

Forgetting the namespace flag

The CoreDNS ConfigMap is named coredns in the kube-system namespace.

3fill in blank

hard

Fix the error in the CoreDNS ConfigMap snippet to correctly forward DNS queries to 8.8.8.8.

Kubernetes

forward . [1]

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

A8.8.8.8:5353

B8.8.8.8

C8.8.8.8:53

D8.8.4.4

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the port number

Using wrong port like 5353

Using wrong IP address

The forward plugin requires the IP and port, so 8.8.8.8:53 is correct.

4fill in blank

hard

Fill both blanks to create a CoreDNS stub domain forwarding example for example.com to 10.0.0.1.

Kubernetes

example.com:53 {
    [1] . [2]
}

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

Aforward

Bproxy

C10.0.0.1

D8.8.8.8

Attempts:

3 left

💡 Hint

Common Mistakes

Using the deprecated proxy plugin

Using wrong IP address

Swapping plugin and IP positions

The forward plugin is used to forward queries for example.com to the IP 10.0.0.1.

5fill in blank

hard

Fill all three blanks to create a CoreDNS hosts plugin block mapping example.com to 10.0.0.2 with TTL 30.

Kubernetes

hosts {
    [1] [2] [3]
    fallthrough
}

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

A10.0.0.2

Bexample.com

C30

Dexample.net

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping domain and IP positions

Using wrong TTL value

Using wrong domain name

The hosts plugin maps example.com to 10.0.0.2 with a TTL of 30 seconds.

Practice

1. What is the main role of CoreDNS in a Kubernetes cluster?

easy

A. To manage container images in the cluster

B. To provide DNS resolution for services and pods inside the cluster

C. To schedule pods on nodes

D. To monitor cluster resource usage

Solution

1. Step 1: Understand CoreDNS function

   CoreDNS acts as the DNS server inside Kubernetes, resolving names of services and pods.

2. Step 2: Compare with other options

   Managing images, scheduling pods, and monitoring are done by other components like container registries, kube-scheduler, and metrics servers.

3. Final Answer:

   To provide DNS resolution for services and pods inside the cluster -> Option B

4. Quick Check:

   CoreDNS = DNS resolution inside Kubernetes [OK]

Hint: CoreDNS is Kubernetes' internal DNS server [OK]

Common Mistakes:

• Confusing CoreDNS with pod scheduling
• Thinking CoreDNS manages container images
• Assuming CoreDNS monitors resources

2. Which Kubernetes resource holds the CoreDNS configuration?

easy

A. Secret named coredns in default namespace

B. Deployment in kube-system namespace

C. ConfigMap named coredns in kube-system namespace

D. ServiceAccount named coredns in kube-system namespace

Solution

1. Step 1: Identify CoreDNS configuration storage

   The CoreDNS configuration is stored in a ConfigMap named 'coredns' inside the 'kube-system' namespace.

2. Step 2: Eliminate other options

   Deployment runs CoreDNS pods but does not hold config; Secrets store sensitive data; ServiceAccounts manage permissions.

3. Final Answer:

   ConfigMap named coredns in kube-system namespace -> Option C

4. Quick Check:

   CoreDNS config = ConfigMap coredns in kube-system [OK]

Hint: CoreDNS config is a ConfigMap in kube-system [OK]

Common Mistakes:

• Confusing ConfigMap with Secret
• Looking in default namespace instead of kube-system
• Thinking Deployment holds config data

3. Inside a pod, you run nslookup kubernetes.default.svc.cluster.local. What is the expected result?

medium

A. An IP address of the Kubernetes API service

B. An error saying domain not found

C. The pod's own IP address

D. The IP address of the CoreDNS pod

Solution

1. Step 1: Understand the DNS query

   The domain 'kubernetes.default.svc.cluster.local' is the default Kubernetes API service DNS name inside the cluster.

2. Step 2: Determine expected DNS resolution

   CoreDNS resolves this to the IP address of the Kubernetes API service, not the pod or CoreDNS pod IP.

3. Final Answer:

   An IP address of the Kubernetes API service -> Option A

4. Quick Check:

   Default service DNS resolves to API server IP [OK]

Hint: Default service DNS resolves to API server IP [OK]

Common Mistakes:

• Expecting pod IP instead of service IP
• Assuming CoreDNS pod IP is returned
• Thinking query fails inside pod

4. You modified the CoreDNS ConfigMap but DNS queries inside pods still fail. What is the most likely fix?

medium

A. Restart the CoreDNS pods to reload the new config

B. Delete all pods in the default namespace

C. Reinstall Kubernetes cluster

D. Change pod DNSPolicy to Default

Solution

1. Step 1: Recognize CoreDNS config reload behavior

   CoreDNS pods need to reload the ConfigMap changes, which usually requires restarting the pods.

2. Step 2: Evaluate other options

   Deleting unrelated pods or reinstalling the cluster is unnecessary; changing DNSPolicy may break cluster DNS.

3. Final Answer:

   Restart the CoreDNS pods to reload the new config -> Option A

4. Quick Check:

   CoreDNS pods restart reloads ConfigMap changes [OK]

Hint: Restart CoreDNS pods after ConfigMap changes [OK]

Common Mistakes:

• Deleting unrelated pods expecting DNS fix
• Reinstalling cluster unnecessarily
• Changing pod DNSPolicy incorrectly

5. You want to add a custom DNS entry for myapp.local inside your Kubernetes cluster using CoreDNS. Which step is required?

hard

A. Deploy a pod named myapp.local with a static IP

B. Create a new Service named myapp.local in default namespace

C. Modify the kubelet to add myapp.local to /etc/hosts on all nodes

D. Add a hosts plugin entry in the CoreDNS ConfigMap with myapp.local mapping

Solution

1. Step 1: Understand how to add custom DNS entries in CoreDNS

   CoreDNS supports a hosts plugin where you can add static hostname-to-IP mappings in its ConfigMap.

2. Step 2: Evaluate other options

   Creating a Service named myapp.local won't create a DNS entry for that domain; modifying kubelet hosts is manual and not scalable; pod names don't create DNS entries.

3. Final Answer:

   Add a hosts plugin entry in the CoreDNS ConfigMap with myapp.local mapping -> Option D

4. Quick Check:

   Custom DNS via hosts plugin in CoreDNS ConfigMap [OK]

Hint: Use hosts plugin in CoreDNS ConfigMap for custom DNS [OK]

Common Mistakes:

• Thinking Service name creates arbitrary DNS names
• Modifying node hosts files manually
• Assuming pod names create DNS entries