- Introduction
- Installation
- Configuration
- Plugins
- Server Blocks
- Common Setups
- Writing Plugins
- Best Practices
CoreDNS is a flexible, extensible DNS server written in Go. Unlike traditional DNS servers, CoreDNS relies heavily on plugins to provide functionality. This modular approach allows for great customization and extensibility.
Key features of CoreDNS:
- Written in Go
- Plugin-based architecture
- Supports various protocols: DNS, DNS over TLS (DoT), DNS over HTTPS (DoH), and DNS over gRPC
- Highly configurable
There are several ways to install CoreDNS:
- Pre-compiled binaries: Available for various operating systems and architectures.
- Docker: Images are available on the public Docker hub.
- From source: Requires a working Go setup and uses Go modules for dependency management.
To test a basic CoreDNS installation:
$ ./coredns -dns.port=1053
$ dig @localhost -p 1053 a whoami.example.orgCoreDNS uses a file called Corefile for configuration. The Corefile consists of one or more Server Blocks, each containing plugin configurations.
CoreDNS supports environment variable substitution in its configuration using the syntax {$ENV_VAR} or {%ENV_VAR%}.
The import plugin allows including other configuration files or snippets.
Snippets are defined using parentheses and can be imported into other parts of the configuration:
(snip) {
prometheus
log
errors
}
. {
whoami
import snip
}
Plugins are the core of CoreDNS functionality. They can:
- Process queries
- Forward queries
- Modify responses
- Implement non-DNS functionality (e.g., metrics, health checks)
The order of plugins in the Corefile does not determine execution order. The execution order is defined in plugin.cfg.
Example plugin configuration:
. {
chaos CoreDNS-001 [email protected]
}
Server Blocks define the zones a server is responsible for and the port it listens on. The basic syntax is:
zone:port {
plugin1
plugin2
}
Multiple zones can be specified in a single Server Block.
Use the file plugin to serve zone data from a file:
example.org {
file db.example.org
log
}
Forward queries to other DNS servers:
. {
forward . 8.8.8.8 9.9.9.9
log
}
Use the unbound plugin (requires recompilation) for recursive resolution:
. {
unbound
cache
log
}
To write a custom plugin:
- Create a
setup.gofile for Corefile parsing - Implement the plugin logic in a separate file (e.g.,
example.go) - Write tests
- Create a
README.mddocumenting the plugin - Include a LICENSE file
Plugins should implement the plugin.Handler interface, which includes the ServeDNS method.
- Use
example.orgorexample.netin examples and tests - Implement
fallthroughfunctionality when appropriate - Follow the style guide for documentation
- Include metrics and readiness reporting
- Use proper logging practices
Remember to check the CoreDNS website and GitHub repository for the most up-to-date information and best practices.
CoreDNS Setup with Custom CA and SSL
Table of Contents
Introduction
This guide will walk you through setting up CoreDNS with a custom Certificate Authority (CA) and SSL certificates for secure local connections. The setup mimics commercial CA operations, providing valid SSL certificates for your local network.
Prerequisites
System Architecture
Step 1: Set Up the Root CA
Create the root CA directory:
Create the root CA configuration file:
Add the following content:
Generate the root CA key:
Generate the root CA certificate:
Verify the root CA certificate:
Step 2: Set Up the Intermediate CA
Create the intermediate CA directory:
Create the intermediate CA configuration file:
Add content similar to the root CA configuration, adjusting paths and CA settings as needed.
Generate the intermediate CA key:
Generate the intermediate CA CSR:
Sign the intermediate CA certificate with the root CA:
Verify the intermediate CA certificate:
Step 3: Install and Configure CoreDNS
Download and install CoreDNS:
Create CoreDNS configuration:
Add the following content:
Create a systemd service for CoreDNS:
Add the following content:
Start and enable CoreDNS:
Step 4: Generate SSL Certificate for hostname.local
Create a certificate signing request (CSR) for hostname.local:
Sign the certificate with the intermediate CA:
Verify the certificate:
Step 5: Configure Client VMs
Copy the root CA certificate to client VMs:
On each client VM, install the root CA certificate:
Configure DNS on client VMs:
Add:
Step 6: Configure SELinux (if applicable)
If you're using SELinux, follow these steps:
Generate a custom SELinux policy for CoreDNS:
Apply the custom policy:
Set correct file contexts:
Troubleshooting
sudo journalctl -u corednsdig @192.168.1.10 hostname.localopenssl s_client -connect hostname.local:443 -CAfile /path/to/ca.cert.pemAdvanced Usage
This README provides a comprehensive guide to setting up CoreDNS with a custom CA and SSL certificates, mimicking commercial CA operations for your local network.