Learning Coredns: Configuring DNS for Cloud Native Environments

Until recently, learning CoreDNS required reading the code or combing through the skimpy documentation on the website. No longer. With this practical book, developers and operators working with Docker or Linux containers will learn how to use this standard DNS server with Kubernetes.

John Belamaric, senior staff software engineer at Google, and Cricket Liu, chief DNS architect at Infoblox, show you how to configure CoreDNS using real-world configuration examples to achieve specific purposes. You’ll learn the basics of DNS, including how it functions as a location broker in container environments and how it ties into Kubernetes.

• Dive into DNS theory: the DNS namespace, domain names, domains, and zones
• Learn how to configure your CoreDNS server
• Manage and serve basic and advanced zone data with CoreDNS
• Configure CoreDNS service discovery with etcd and Kubernetes
• Learn one of the most common use cases for CoreDNS: the integration with Kubernetes
• Manipulate queries and responses as they flow through the plug-in chain
• Monitor and troubleshoot the availability and performance of your DNS service
• Build custom versions of CoreDNS and write your own plug-ins
Table of contents :
Cover
Copyright
Table of Contents
Preface
Why a New DNS Server?
Who Needs CoreDNS?
Who This Book Is For
What You Will Learn
Conventions Used in This Book
Using Code Examples
O’Reilly Online Learning
How to Contact Us
Acknowledgments
Chapter 1. Introduction
What Is CoreDNS?
CoreDNS, Containers, and Microservices
CoreDNS Limitations
CoreDNS, Kubernetes, and the Cloud Native Computing Foundation
Chapter 2. A DNS Refresher
What Is the Domain Name System?
Domain Names and the Namespace
Domains, Delegation, and Zones
Resource Records
DNS Servers and Authority
Resolvers
Resolution and Recursion
Caching
Resource Records
NAME
TTL
CLASS
Resource Record Types
The A Record
The AAAA Record
The CNAME Record
The MX Record
The NS Record
The SRV Record
The PTR Record
The SOA Record
An Annotated Zone Data File
Chapter 3. Configuring CoreDNS
Getting CoreDNS
CoreDNS Command-Line Options
Corefile Syntax
Environment Variables
Reusable Snippets
Import
Server Blocks
Query Processing
Plug-ins
Root
File
Secondary
Forward
Cache
Errors
Log
Common Configuration Options
fallthrough
tls
transfer to
Sample DNS Server Configurations
Caching-Only DNS Server
Primary DNS Server
Secondary DNS Server
Chapter 4. Managing Zone Data
The file Plug-in
The auto Plug-in
Using the auto Plug-in with Git
The hosts Plug-in
The route53 plug-in
Chapter 5. Service Discovery
Introduction to Service Discovery
Solving the Service Discovery Problem
Service Discovery with CoreDNS and etcd
The etcd Plug-in
Other Service Discovery Options
Service Discovery and Container Orchestration
Chapter 6. Kubernetes
Basic Concepts
Kubernetes Networking
Cluster IP Services
Headless Services
Kubernetes DNS Specification
CoreDNS Integration
Default Configuration
Stub Domains and Federations
Cluster DNS Deployment Resources
Role-Based Access Control
Service
Deployment
Autoscaling
A Better Configuration
The kubernetes Plug-in
CoreDNS Extensions
Pod Options
Wildcard Queries
Autopath and the Dreaded ndots:5
Zone Transfer Support
Exposing Services Externally
Modifying the Available Records
Chapter 7. Manipulating Queries and Responses
The template Plug-in
The rewrite Plug-in
Using the rewrite Plug-in for EDNS0 Options
Multiple rewrite Rules
The metadata Plug-in
Signing Responses with the DNS Security Extensions
Managing a DNSSEC-Signed Primary Zone
On-the-Fly DNSSEC Signing with the dnssec Plug-in
Case Study: Infoblox’s BloxOne Threat Defense
Identifying Users
Applying Policy
Chapter 8. Monitoring and Troubleshooting
The prometheus Plug-in
The log Plug-in
The dnstap Plug-in
The errors Plug-in
The trace Plug-in
The debug Plug-in
Chapter 9. Building a Custom Server
Compiling CoreDNS with an External Plug-in
Building Using Docker
Building on Your Workstation
Modifying plugin.cfg
Replacing main
Writing a Custom Plug-in
There Can Be Only One
Integrating with Metrics, Trace, and Metadata
Index
About the Authors
Colophon