compreshensive-coredns.md

CoreDNS: A Comprehensive Overview

Table of Contents

1. Introduction
2. Installation
3. Configuration
4. Plugins
5. Server Blocks
6. Common Setups
7. Writing Plugins
8. Best Practices

Introduction

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

Installation

There are several ways to install CoreDNS:

1. Pre-compiled binaries: Available for various operating systems and architectures.
2. Docker: Images are available on the public Docker hub.
3. 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.org

Configuration

CoreDNS uses a file called Corefile for configuration. The Corefile consists of one or more Server Blocks, each containing plugin configurations.

Environment Variables

CoreDNS supports environment variable substitution in its configuration using the syntax {$ENV_VAR} or {%ENV_VAR%}.

Importing Other Files

The import plugin allows including other configuration files or snippets.

Reusable Snippets

Snippets are defined using parentheses and can be imported into other parts of the configuration:

(snip) {
    prometheus
    log
    errors
}

. {
    whoami
    import snip
}

Plugins

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

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.

Common Setups

Authoritative Serving from Files

Use the file plugin to serve zone data from a file:

example.org {
    file db.example.org
    log
}

Forwarding

Forward queries to other DNS servers:

. {
    forward . 8.8.8.8 9.9.9.9
    log
}

Recursive Resolver

Use the unbound plugin (requires recompilation) for recursive resolution:

. {
    unbound
    cache
    log
}

Writing Plugins

To write a custom plugin:

1. Create a setup.go file for Corefile parsing
2. Implement the plugin logic in a separate file (e.g., example.go)
3. Write tests
4. Create a README.md documenting the plugin
5. Include a LICENSE file

Plugins should implement the plugin.Handler interface, which includes the ServeDNS method.

Best Practices

1. Use example.org or example.net in examples and tests
2. Implement fallthrough functionality when appropriate
3. Follow the style guide for documentation
4. Include metrics and readiness reporting
5. Use proper logging practices

Remember to check the CoreDNS website and GitHub repository for the most up-to-date information and best practices.

CoreDNS and OpenXPKI Setup Guide

Table of Contents

1. Introduction
2. Prerequisites
3. System Architecture
4. Step 1: Install OpenXPKI
5. Step 2: Configure OpenXPKI
6. Step 3: Set Up Root CA and Issuing CA
7. Step 4: Install and Configure CoreDNS
8. Step 5: Generate SSL Certificate for hostname.local
9. Step 6: Configure Client VMs
10. Step 7: Configure SELinux (if applicable)
11. Troubleshooting
12. Advanced Usage

Introduction

This guide will walk you through setting up CoreDNS with OpenXPKI for certificate management, providing a robust local DNS infrastructure with valid SSL certificates.

Prerequisites

• 1 Debian VM for CoreDNS server and OpenXPKI
• 2 Client VMs (any Linux distribution)
• Root or sudo access on all VMs
• Basic understanding of DNS, SSL, and networking concepts

System Architecture

• Server VM: Hosts CoreDNS and OpenXPKI
• Client VMs: Use CoreDNS for local resolution and trust the OpenXPKI CA

Step 1: Install OpenXPKI

1. Update your system and install dependencies:

   sudo apt update
   sudo apt upgrade -y
   sudo apt install -y libopenca-perl libopenxpki-perl openxpki-i18n

2. Install OpenXPKI:

   sudo apt install -y openxpki

Step 2: Configure OpenXPKI

1. Initialize the OpenXPKI configuration:

   sudo openxpkiadm init

2. Create a new realm (replace "Local-CA" with your desired realm name):

   sudo openxpkiadm realm create --realm Local-CA

3. Edit the OpenXPKI configuration file:

   sudo nano /etc/openxpki/config.d/realm/Local-CA/system/crypto.yaml

   Adjust the key sizes and algorithms as needed:

   type: OpenXPKI::Crypto::Backend::OpenSSL
   
   key:
       default:
           algorithm: rsa
           key_length: 4096
           enc_alg: aes256
   
   hash: sha256

4. Configure the certificate profiles in /etc/openxpki/config.d/realm/Local-CA/profile/:
   Create or edit files for your certificate profiles (e.g., I18N_OPENXPKI_PROFILE_TLS_SERVER.yaml for server certificates).

Step 3: Set Up Root CA and Issuing CA

1. Generate the Root CA:

   sudo openxpkiadm certificate init --realm Local-CA --token root

2. Generate the Issuing CA:

   sudo openxpkiadm certificate init --realm Local-CA --token ca-signer

3. Start the OpenXPKI service:

   sudo systemctl start openxpki.service
   sudo systemctl enable openxpki.service

Step 4: Install and Configure CoreDNS

1. Download and install CoreDNS:

   wget https://github.com/coredns/coredns/releases/download/v1.10.1/coredns_1.10.1_linux_amd64.tgz
   tar xzf coredns_1.10.1_linux_amd64.tgz
   sudo mv coredns /usr/local/bin/

2. Create CoreDNS configuration:

   sudo mkdir /etc/coredns
   sudo nano /etc/coredns/Corefile

   Add the following content:

   .:53 {
       hosts {
           192.168.1.10 server.local
           192.168.1.20 client1.local
           192.168.1.30 client2.local
           fallthrough
       }
       forward . 1.1.1.1
       log
       errors
   }
   

3. Create a systemd service for CoreDNS:

   sudo nano /etc/systemd/system/coredns.service

   Add the following content:

   [Unit]
   Description=CoreDNS DNS server
   After=network.target
   
   [Service]
   ExecStart=/usr/local/bin/coredns -conf /etc/coredns/Corefile
   Restart=on-failure
   
   [Install]
   WantedBy=multi-user.target

4. Start and enable CoreDNS:

   sudo systemctl daemon-reload
   sudo systemctl start coredns
   sudo systemctl enable coredns

Step 5: Generate SSL Certificate for hostname.local

1. Create a certificate signing request (CSR) for hostname.local:

   openssl req -new -newkey rsa:2048 -nodes -keyout hostname.local.key -out hostname.local.csr

2. Submit the CSR to OpenXPKI:

   openxpki-cli request create --subject "CN=hostname.local" --format pkcs10 --csr hostname.local.csr

3. Approve and issue the certificate:

   openxpki-cli workflow start --workflow certificate_signing_request_v2 --param cert_profile=tls-server --param cert_subject_style=00_basic_style

   Follow the prompts to approve and issue the certificate.

4. Retrieve the issued certificate:

   openxpki-cli certificate get --format PEM > hostname.local.crt

Step 6: Configure Client VMs

1. Export the Root CA certificate:

   openxpki-cli certificate get --format PEM --realm Local-CA --issuer root > root-ca.crt

2. Copy the Root CA certificate to client VMs:

   scp root-ca.crt user@client-vm:/tmp/

3. On each client VM, install the Root CA certificate:

   sudo cp /tmp/root-ca.crt /usr/local/share/ca-certificates/openxpki-root-ca.crt
   sudo update-ca-certificates

4. Configure DNS on client VMs:

   sudo nano /etc/resolv.conf

   Add:

   nameserver 192.168.1.10  # CoreDNS server IP
   

Step 7: Configure SELinux (if applicable)

If you're using SELinux, follow these steps:

1. Generate a custom SELinux policy for CoreDNS:

   sudo ausearch -c 'coredns' --raw | audit2allow -M my-coredns

2. Apply the custom policy:

   sudo semodule -i my-coredns.pp

3. Set correct file contexts:

   sudo semanage fcontext -a -t bin_t "/usr/local/bin/coredns"
   sudo restorecon -v /usr/local/bin/coredns
   sudo semanage fcontext -a -t etc_t "/etc/coredns(/.*)?"
   sudo restorecon -R -v /etc/coredns

Troubleshooting

• Check OpenXPKI logs: sudo journalctl -u openxpki
• Check CoreDNS logs: sudo journalctl -u coredns
• Verify DNS resolution: dig @192.168.1.10 hostname.local
• Test SSL: openssl s_client -connect hostname.local:443 -CAfile /path/to/root-ca.crt

Advanced Usage

• Set up a web interface for OpenXPKI for easier certificate management
• Implement automatic certificate renewal using OpenXPKI's REST API
• Configure CoreDNS to use DNS-over-TLS (DoT) or DNS-over-HTTPS (DoH) for enhanced security

This guide provides a comprehensive setup for CoreDNS with OpenXPKI, allowing you to manage your own Certificate Authority and issue valid SSL certificates for your local network.

SSL Setup with CoreDNS and OpenXPKI

Table of Contents

1. Introduction
2. System Overview
3. Setup Process
4. Component Interactions
5. Project Timeline
6. Implementation Guide
7. Best Practices
8. Troubleshooting
9. Additional Resources

Introduction

This README provides a comprehensive guide for setting up a secure SSL infrastructure using CoreDNS for DNS management and OpenXPKI for certificate authority operations. This setup is designed for organizations requiring a robust, scalable, and secure internal PKI solution.

System Overview

The following diagram presents a high-level overview of the SSL setup:

Key components:

• CoreDNS: Manages DNS resolution for the network
• OpenXPKI: Acts as the Certificate Authority (CA) for issuing and managing SSL certificates
• Client VMs: Endpoints that will use the SSL certificates and CoreDNS for secure communication

Setup Process

The setup process involves several key steps, as illustrated in this flowchart:

This flowchart outlines the entire process from initial setup to final testing. Color coding helps distinguish different types of steps:

• Green: Start/End points
• Blue: Processes
• Yellow: Decision points

Component Interactions

To understand how different parts of the system interact, refer to this diagram:

This diagram shows:

• How client VMs interact with CoreDNS for DNS queries
• The role of OpenXPKI in issuing SSL certificates
• The connection to external DNS (1.1.1.1) for resolving internet domains

Implementation Guide

1. Set up Server Infrastructure

   • Prepare server(s) for CoreDNS and OpenXPKI
   • Ensure network connectivity

2. Install and Configure OpenXPKI

   • Set up Root CA
   • Configure Issuing CA

3. Install and Configure CoreDNS

   • Set up DNS zones
   • Configure forwarding rules

4. Generate and Deploy SSL Certificates

   • Use OpenXPKI to generate certificates
   • Deploy certificates to required services

5. Configure Client VMs

   • Install Root CA certificate
   • Update DNS settings to use CoreDNS

6. Implement Security Measures

   • Configure firewalls
   • Set up SELinux/AppArmor if applicable

7. Testing and Verification

   • Test DNS resolution
   • Verify SSL certificate validity
   • Check secure connections between services

Best Practices

1. Regular Updates: Keep all components up-to-date with the latest security patches.
2. Backup: Regularly backup CA keys and certificates.
3. Monitoring: Implement monitoring for both CoreDNS and OpenXPKI.
4. Access Control: Use strong authentication for administrative access.
5. Documentation: Maintain clear, up-to-date documentation of the setup and processes.

Troubleshooting

Common issues and solutions:

1. Certificate Issuance Failures

   • Check OpenXPKI logs
   • Verify CA certificate validity

2. DNS Resolution Problems

   • Ensure CoreDNS is running
   • Check CoreDNS configuration

3. Client Connection Issues

   • Verify Root CA certificate installation on clients
   • Check client DNS settings

Additional Resources

• CoreDNS Documentation
• OpenXPKI User Guide
• SSL/TLS Best Practices

Project Timeline

For project planning, use this Gantt chart as a reference:

This timeline provides:

• A breakdown of major tasks
• Estimated durations for each phase
• Dependencies between different stages of the setup