Understanding and resolving DNS issues in Kubernetes can be challenging. This workshop is designed to equip you with the skills and knowledge needed to effectively troubleshoot DNS problems in a Kubernetes environment.

Introduction to DNS in Kubernetes

A brief introduction to DNS and its role in Kubernetes. We’ll also discuss the importance of DNS in Kubernetes and how it differs from traditional DNS solutions.

Overview

We’ll start by understanding the role and significance of DNS in Kubernetes. DNS is crucial for service discovery and connectivity within a Kubernetes cluster.

CoreDNS and Kubernetes DNS Service

A brief introduction to CoreDNS, the default DNS server used in Kubernetes, and how it differs from traditional DNS solutions. We’ll also touch upon the Kubernetes DNS service, which translates service and pod names into IP addresses.

Example Command: kubectl get svc -n kube-system - To view the Kubernetes DNS service.

Key Takeaways

  • Understanding of Kubernetes DNS basics.
  • Introduction to CoreDNS and its role in Kubernetes.
  • Insights into the Kubernetes DNS service’s functionality.

Note: RKE1, RKE2, and k3s use CoreDNS as the default DNS server even tho the service is named kube-dns.

Understanding CoreDNS

A deep dive into CoreDNS, its architecture, and how it integrates with Kubernetes. CoreDNS is a flexible and extensible DNS server, which can be customized using plugins.

CoreDNS in Kubernetes

Delve into the details of CoreDNS, its architecture, and how it integrates with Kubernetes. CoreDNS is a flexible and extensible DNS server, which can be customized using plugins.

Example Command: kubectl describe configmap coredns -n kube-system - To view CoreDNS configurations.

Configuration and Plugins

Learn about the basic configuration of CoreDNS in Kubernetes and how plugins can be used to enhance its functionality.

Key Takeaways

  • In-depth understanding of CoreDNS.
  • Knowledge of CoreDNS configuration and plugins in Kubernetes.

Kubernetes DNS Architecture

A detailed look at the Kubernetes DNS architecture and how it works. We’ll also discuss the role of the Kubernetes DNS service in the cluster.

Kubernetes DNS Architecture

DNS Components in Kubernetes

Explore the components of DNS in Kubernetes, including the role of kube-dns, CoreDNS, and how they interact with pods and services.

Diagram Suggestion: A flowchart showing how a DNS query travels through a Kubernetes cluster.

DNS Workflow

Understand the workflow of a DNS query in a Kubernetes cluster, from a pod requesting a service to the resolution of the service’s IP address.

Diagram Suggestion: Illustrate the sequence of events in a DNS resolution within Kubernetes.

Key Takeaways

  • Clear understanding of Kubernetes DNS architecture.
  • Insights into the DNS query workflow in Kubernetes.

Common DNS Issues and Solutions

A discussion on common DNS issues in Kubernetes and how to resolve them. We’ll also touch upon the best practices for maintaining healthy DNS in Kubernetes.

Debugging DNS Resolution

Explore how to identify and solve DNS resolution problems within Kubernetes pods and services.

Example Command: kubectl exec <pod-name> -- nslookup <service-name> - To test DNS resolution inside a pod.

Diagram Suggestion: Flowchart illustrating common DNS resolution issues and troubleshooting steps.

Key Takeaways

  • Techniques to diagnose DNS resolution problems.
  • Understanding common patterns in DNS issues within Kubernetes.

Analyzing CoreDNS Logs

Learn the art of reading and understanding CoreDNS logs to troubleshoot DNS issues effectively.

Example Command: kubectl logs -n kube-system -l k8s-app=kube-dns - To view CoreDNS logs.

Practical Tips: Guidance on identifying key log entries that signify DNS issues and how to interpret them.

Key Takeaways

  • Skills to analyze CoreDNS logs.
  • Ability to identify DNS issues from log entries.

Advanced Troubleshooting Techniques

Advanced methods for diagnosing and resolving complex DNS issues in Kubernetes.

Customizing CoreDNS Configuration

Detailed walkthrough on tailoring CoreDNS configuration to address specific DNS challenges in your Kubernetes cluster.

Example Command: kubectl edit configmap coredns -n kube-system - To modify CoreDNS configurations.

Practical Exercise: Participants will practice modifying a CoreDNS configmap to address a simulated DNS issue.

Key Takeaways

  • Knowledge of advanced CoreDNS configuration.
  • Hands-on experience in customizing CoreDNS settings.

Network Policies and DNS

Understand how Kubernetes network policies can impact DNS resolution and learn strategies to configure them for optimal DNS functionality.

Example Command: kubectl describe netpol <policy-name> - To examine a network policy affecting DNS.

Diagram Suggestion: Visual representation of how network policies can block or allow DNS traffic in a Kubernetes cluster.

Key Takeaways

  • Insights into the interaction between network policies and DNS.
  • Strategies for configuring network policies to support DNS operations.

Lab Exercises

Hands-on lab exercises to reinforce the concepts covered in the workshop.

Lab 1: Pod DNS Resolution

Lab 1.0: Setup

apiVersion: v1
kind: Pod
metadata:
  name: dns-troubleshoot-pod
spec:
  containers:
  - name: swiss-army-knife
    image: rancherlab/swiss-army-knife
    command:
      - sleep
      - "3600"
  dnsPolicy: Broken

Lab 1.1: Debug

Can the pod resolve the service name?

Example Command: kubectl exec dns-troubleshoot-pod -- nslookup kubernetes.default - To test DNS resolution inside a pod.

Can the pod resolve an external domain name?

Example Command: kubectl exec dns-troubleshoot-pod -- nslookup google.com - To test DNS resolution inside a pod.

What IP address is the pod using for DNS resolution?

Example Command: kubectl exec dns-troubleshoot-pod -- cat /etc/resolv.conf - To view the DNS configuration inside a pod.

Lab 1.2: Fix

Modify the pod’s DNS configuration to use a custom DNS server.

apiVersion: v1
kind: Pod
metadata:
  name: dns-troubleshoot-pod
spec:
  containers:
  - name: swiss-army-knife
    image: rancherlab/swiss-army-knife
    command:
      - sleep
      - "3600"
  dnsPolicy: Default

Lab 2: CoreDNS Performance Issues

Lab 2.0: Setup

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |
    .:53 {
        errors
        health
        log  # Excessive logging for simulation
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        forward . /etc/resolv.conf {
            max_concurrent 1
        }
        cache 30
        loop
        reload
        loadbalance
    }

Lab 2.1: Debug

How long does it take for a pod to resolve a service name?

Example Command: kubectl exec dns-troubleshoot-pod -- time nslookup kubernetes.default - To test DNS resolution inside a pod.

Lab 2.2: Fix

Modify the CoreDNS configuration to use high performance settings.

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |
    .:53 {
        errors
        health
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        forward . /etc/resolv.conf {
            max_concurrent 1000  # Allowing a high number of concurrent queries
        }
        cache {
            success 512 30  # Caching successful responses
            denial 512 5   # Caching denial responses
        }
        reload
        loadbalance
    }

Alternatively, you can use nodeLocal DNSCache to improve DNS performance.

Useful Tools

A list of tools that can be used to troubleshoot DNS issues in Kubernetes.