Using Kubernetes Services with DNS

Introduction

Kubernetes Services can be located with the Kubernetes DNS just like Pods can. In this lab, you will work with the Kubernetes DNS to discover Services from within a Pod. This will test your knowledge of how to interact with Services using DNS.

Solution

Log in to the control plane server using the credentials provided:

ssh cloud_user@<PUBLIC_IP_ADDRESS>

Perform an Nslookup for a Service in the Same Namespace

1. Start using the busybox Pod in the web namespace to perform an nslookup on the web-frontend Service by entering:

   kubectl exec -n web busybox -- nslookup web-frontend
   

2. Redirect the output to save the results in a text file by using:

   kubectl exec -n web busybox -- nslookup web-frontend >> ~/dns_same_namespace_results.txt
   

3. Look up the same Service using the fully qualified domain name by entering:

   kubectl exec -n web busybox -- nslookup web-frontend.web.svc.cluster.local
   

4. Redirect the output to save the results of the second nslookup in a text file by using:

   kubectl exec -n web busybox -- nslookup web-frontend.web.svc.cluster.local >> ~/dns_same_namespace_results.txt
   

5. Check that everything looks okay in the text file by using:

   cat ~/dns_same_namespace_results.txt
   

6. Use clear to clear the text file output.

Perform an Nslookup For a Service in a Different Namespace

1. Use the busybox Pod in the web namespace to perform an nslookup on the user-db Service in the data namespace, while only utilizing the short Service name, by entering:

   kubectl exec -n web busybox -- nslookup user-db
   

   This first request is supposed to result in an error message, so don’t be alarmed if you see that we can’t resolve user-db.

2. Save the results of this nslookup in a text file by using:

   kubectl exec -n web busybox -- nslookup user-db >> ~/dns_different_namespace_results.txt
   

3. Perform the same lookup using the fully qualified domain name by entering:

   kubectl exec -n web busybox -- nslookup user-db.data.svc.cluster.local
   

4. Save the results in a text file by using:

   kubectl exec -n web busybox -- nslookup user-db.data.svc.cluster.local >> ~/dns_different_namespace_results.txt
   

5. Check the output in the text file by using:

   cat ~/dns_different_namespace_results.txt