- 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.
Secure Service Mesh Setup Guide with CoreDNS and OpenXPKI/EJBCA
Table of Contents
1. Introduction
This guide will walk you through setting up a secure service mesh using Cilium, CoreDNS, and either OpenXPKI or EJBCA for certificate management. This setup will provide service discovery, mutual TLS (mTLS) authentication, and network policy enforcement without the need for Kubernetes.
2. Prerequisites
3. Set Up Cilium on Linux VMs
Install Cilium on each VM:
Configure Cilium in standalone mode:
Create a file
/etc/cilium/cilium.yamlwith the following content:Start Cilium:
4. Install and Configure CoreDNS
Install CoreDNS:
Create a CoreDNS configuration file
/etc/coredns/Corefile:Install and configure etcd:
Start CoreDNS:
Update
/etc/resolv.confon all VMs to use CoreDNS:5. Set Up Certificate Authority (OpenXPKI or EJBCA)
Choose either OpenXPKI or EJBCA as your Certificate Authority:
Option A: OpenXPKI
Install OpenXPKI:
Configure OpenXPKI (basic setup):
Create a Root CA and Issuing CA:
Option B: EJBCA
Install EJBCA:
wget https://sourceforge.net/projects/ejbca/files/ejbca6/ejbca_6_15_2_6/ejbca-ce-6.15.2.6.zip unzip ejbca-ce-6.15.2.6.zip cd ejbca-ce-6.15.2.6 ant deployConfigure EJBCA (basic setup):
6. Configure Services for mTLS
For each service:
Generate a certificate signing request (CSR):
Submit the CSR to your CA (OpenXPKI or EJBCA) and obtain a signed certificate.
Configure your service to use the certificate and private key for mTLS.
7. Integrate Cilium with Certificate-based Authentication
Create a Cilium network policy that uses certificate information:
Apply the policy:
8. Test and Validate the Setup
Verify DNS resolution:
Test mTLS communication between services:
Verify Cilium network policies:
This guide provides a comprehensive approach to setting up a secure service mesh using CoreDNS and either OpenXPKI or EJBCA for certificate management. It covers service discovery, mutual TLS authentication, and network policy enforcement without the need for Kubernetes.
Remember to adapt the configurations and commands to your specific environment and requirements. Always follow best practices for security and keep your systems updated.