CoreDNS Task Service
Overview
The CoreDNS task service provides a complete installation and configuration of CoreDNS, a DNS server written in Go that chains plugins. CoreDNS is the default DNS server for Kubernetes and can also serve as a general-purpose authoritative or recursive DNS server with advanced features like service discovery, load balancing, and integration with various backends.
Features
Core DNS Capabilities
- Authoritative DNS - Serve DNS records for your domains
- Recursive DNS - Forward queries to upstream DNS servers
- Zone File Support - Traditional DNS zone file management
- Dynamic Records - Real-time DNS record updates
- Service Discovery - Integration with service discovery systems
Plugin Architecture
- Modular Design - Extensible plugin-based architecture
- Built-in Plugins - Comprehensive set of built-in plugins
- Custom Plugins - Support for custom plugin development
- Plugin Chaining - Chain multiple plugins for complex DNS scenarios
- Hot Reload - Configuration changes without service restart
Advanced Features
- Load Balancing - Multiple DNS resolution strategies
- Health Checking - Monitor upstream server health
- Metrics & Monitoring - Prometheus metrics integration
- Logging - Structured logging with multiple output formats
- TLS/DoT Support - DNS over TLS for secure queries
Integration Capabilities
- Kubernetes Integration - Native Kubernetes service discovery
- Etcd Backend - Store DNS records in etcd
- Cloud DNS - Integration with cloud DNS providers
- External Data - Integration with external databases and APIs
- DNSSEC Support - DNS Security Extensions
Configuration
Basic Configuration
coredns: COREDNS = {
name: "coredns"
version: "1.11.1"
hostname: "dns-server"
etc_corefile: "/etc/coredns/Corefile"
nameservers: [
{ns_ip: "8.8.8.8"},
{ns_ip: "8.8.4.4"}
]
domains_search: "cluster.local"
entries: [
{
domain: "."
port: 53
forward: {
source: "."
forward_ip: "8.8.8.8"
}
use_log: true
use_errors: true
use_cache: true
}
]
}
Production DNS Server
coredns: COREDNS = {
name: "coredns"
version: "1.11.1"
hostname: "production-dns"
etc_corefile: "/etc/coredns/Corefile"
nameservers: [
{ns_ip: "1.1.1.1"},
{ns_ip: "1.0.0.1"},
{ns_ip: "8.8.8.8"}
]
domains_search: "company.com cluster.local"
entries: [
{
domain: "company.com"
port: 53
file: "/etc/coredns/company.com.db"
records: [
{
name: "www"
ttl: 300
rectype: "A"
target_ip: "203.0.113.10"
comment: "Main website"
},
{
name: "api"
ttl: 300
rectype: "A"
target_ip: "203.0.113.20"
comment: "API server"
},
{
name: "mail"
ttl: 300
rectype: "MX"
value: "10 mail.company.com"
comment: "Mail server"
}
]
use_log: true
use_errors: true
use_cache: true
},
{
domain: "."
port: 53
forward: {
source: "."
forward_ip: "1.1.1.1"
}
use_log: true
use_errors: true
use_cache: true
}
]
}
Kubernetes DNS Configuration
coredns: COREDNS = {
name: "coredns"
version: "1.11.1"
hostname: "k8s-dns"
etc_corefile: "/etc/coredns/Corefile"
nameservers: [
{ns_ip: "8.8.8.8"},
{ns_ip: "8.8.4.4"}
]
domains_search: "cluster.local svc.cluster.local"
entries: [
{
domain: "cluster.local"
port: 53
use_log: true
use_errors: true
use_cache: true
etcd_cluster_name: "kubernetes"
},
{
domain: "in-addr.arpa"
port: 53
use_log: true
use_errors: true
use_cache: true
},
{
domain: "ip6.arpa"
port: 53
use_log: true
use_errors: true
use_cache: true
},
{
domain: "."
port: 53
forward: {
source: "."
forward_ip: "8.8.8.8"
}
use_log: true
use_errors: true
use_cache: true
}
]
}
Multi-Zone Configuration
coredns: COREDNS = {
name: "coredns"
version: "1.11.1"
hostname: "multi-zone-dns"
etc_corefile: "/etc/coredns/Corefile"
nameservers: [
{ns_ip: "1.1.1.1"},
{ns_ip: "8.8.8.8"}
]
domains_search: "internal.company.com external.company.com"
entries: [
{
domain: "internal.company.com"
port: 53
file: "/etc/coredns/internal.db"
records: [
{
name: "db1"
ttl: 300
rectype: "A"
target_ip: "10.0.1.100"
},
{
name: "app1"
ttl: 300
rectype: "A"
target_ip: "10.0.1.200"
},
{
name: "load-balancer"
ttl: 60
rectype: "A"
target_ip: "10.0.1.10"
}
]
use_log: true
use_errors: true
use_cache: true
},
{
domain: "external.company.com"
port: 53
file: "/etc/coredns/external.db"
records: [
{
name: "www"
ttl: 3600
rectype: "CNAME"
value: "cdn.cloudflare.com"
},
{
name: "blog"
ttl: 300
rectype: "A"
target_ip: "203.0.113.50"
}
]
use_log: true
use_errors: true
use_cache: true
}
]
}
High-Availability Configuration
coredns: COREDNS = {
name: "coredns"
version: "1.11.1"
hostname: "ha-dns-primary"
etc_corefile: "/etc/coredns/Corefile"
nameservers: [
{ns_ip: "1.1.1.1"},
{ns_ip: "1.0.0.1"},
{ns_ip: "8.8.8.8"},
{ns_ip: "8.8.4.4"}
]
domains_search: "company.com"
entries: [
{
domain: "company.com"
port: 53
file: "/etc/coredns/company.com.db"
records: [
{
name: "@"
ttl: 300
rectype: "SOA"
value: "ns1.company.com. admin.company.com. 2024010101 3600 1800 604800 86400"
},
{
name: "@"
ttl: 300
rectype: "NS"
value: "ns1.company.com."
},
{
name: "@"
ttl: 300
rectype: "NS"
value: "ns2.company.com."
},
{
name: "ns1"
ttl: 300
rectype: "A"
target_ip: "203.0.113.10"
},
{
name: "ns2"
ttl: 300
rectype: "A"
target_ip: "203.0.113.11"
}
]
use_log: true
use_errors: true
use_cache: true
}
]
}
Usage
Deploy CoreDNS
./core/nulib/provisioning taskserv create coredns --infra <infrastructure-name>
List Available Task Services
./core/nulib/provisioning taskserv list
SSH to CoreDNS Server
./core/nulib/provisioning server ssh <coredns-server>
Service Management
# Check CoreDNS status
systemctl status coredns
# Start/stop CoreDNS
systemctl start coredns
systemctl stop coredns
systemctl restart coredns
# View CoreDNS logs
journalctl -u coredns -f
# Check CoreDNS version
coredns -version
DNS Testing
# Test DNS resolution
dig @localhost google.com
nslookup google.com localhost
# Test specific record types
dig @localhost company.com MX
dig @localhost company.com NS
dig @localhost company.com SOA
# Test reverse DNS
dig @localhost -x 8.8.8.8
# Performance testing
drill @localhost google.com
Configuration Management
# Validate Corefile syntax
coredns -conf /etc/coredns/Corefile -dry
# Check loaded plugins
coredns -plugins
# Reload configuration (if enabled)
systemctl reload coredns
# View current configuration
cat /etc/coredns/Corefile
Zone File Management
# Check zone file syntax
named-checkzone company.com /etc/coredns/company.com.db
# View zone records
cat /etc/coredns/company.com.db
# Update zone file
sudo vi /etc/coredns/company.com.db
sudo systemctl reload coredns
Monitoring and Debugging
# Check DNS metrics (if Prometheus plugin enabled)
curl http://localhost:9153/metrics
# Debug DNS queries
tail -f /var/log/coredns/query.log
# Check plugin status
coredns -conf /etc/coredns/Corefile -plugins
# Network troubleshooting
netstat -tlnp | grep :53
ss -tulpn | grep :53
Architecture
System Architecture
┌─────────────────┐ ┌──────────────────┐ ┌─────────────────┐
│ DNS Clients │────│ CoreDNS │────│ Backends │
│ │ │ │ │ │
│ • Applications │ │ • Plugin Chain │ │ • Zone Files │
│ • Services │────│ • Query Router │────│ • Etcd │
│ • Resolvers │ │ • Cache Layer │ │ • External DNS │
│ • Load Balancer │ │ • Health Checks │ │ • Databases │
└─────────────────┘ └──────────────────┘ └─────────────────┘
Plugin Chain Architecture
┌─────────────────────────────────────────────────────────────┐
│ DNS Query Flow │
├─────────────────────────────────────────────────────────────┤
│ Input Plugin │ Processing Plugins │ Output Plugin │
│ │ │ │
│ • bind │ • cache │ • forward │
│ • health │ • rewrite │ • file │
│ • ready │ • template │ • auto │
│ • prometheus │ • loadbalance │ • etcd │
│ • log │ • dnssec │ • kubernetes │
├─────────────────────────────────────────────────────────────┤
│ Error Handling │
│ │
│ • errors • whoami • debug │
│ • trace • chaos • reload │
└─────────────────────────────────────────────────────────────┘
File Structure
/etc/coredns/ # Configuration directory
├── Corefile # Main configuration file
├── company.com.db # Zone files
├── internal.db # Internal zone file
└── external.db # External zone file
/var/lib/coredns/ # Data directory
├── cache/ # DNS cache data
├── zones/ # Dynamic zone data
└── logs/ # Log files
/var/log/coredns/ # Log directory
├── query.log # Query logs
├── error.log # Error logs
└── access.log # Access logs
Supported Operating Systems
- Ubuntu 20.04+ / Debian 11+
- CentOS 8+ / RHEL 8+ / Fedora 35+
- Amazon Linux 2+
- SUSE Linux Enterprise 15+
System Requirements
Minimum Requirements
- RAM: 512MB (1GB+ recommended)
- Storage: 5GB (10GB+ for extensive logging)
- CPU: 1 core (2+ cores recommended)
- Network: UDP/TCP port 53 access
Production Requirements
- RAM: 2GB+ (depends on cache size and query volume)
- Storage: 20GB+ SSD
- CPU: 2+ cores
- Network: High bandwidth, low latency
Network Requirements
- Port 53 - DNS queries (UDP/TCP)
- Port 9153 - Metrics endpoint (optional)
- Port 8080 - Health check endpoint (optional)
- Firewall - Allow inbound DNS traffic
Troubleshooting
Service Issues
# Check service status
systemctl status coredns
# View detailed logs
journalctl -u coredns --no-pager -l
# Check configuration syntax
coredns -conf /etc/coredns/Corefile -dry
# Test plugin loading
coredns -conf /etc/coredns/Corefile -plugins
DNS Resolution Issues
# Test local resolution
dig @127.0.0.1 google.com
# Check upstream connectivity
dig @8.8.8.8 google.com
# Test specific zones
dig @localhost company.com SOA
# Debug query path
dig @localhost +trace google.com
Performance Issues
# Check resource usage
top -p $(pgrep coredns)
ps aux | grep coredns
# Monitor DNS queries
tail -f /var/log/coredns/query.log
# Check cache hit ratio
curl http://localhost:9153/metrics | grep coredns_cache
# Network performance
iftop -i eth0 -f "port 53"
Configuration Issues
# Validate Corefile
coredns -conf /etc/coredns/Corefile -dry
# Check zone file syntax
named-checkzone company.com /etc/coredns/company.com.db
# Test configuration reload
sudo systemctl reload coredns
# Check file permissions
ls -la /etc/coredns/
Network Connectivity
# Check port binding
netstat -tlnp | grep :53
ss -tulpn | grep coredns
# Test external connectivity
telnet 8.8.8.8 53
# Check firewall rules
sudo iptables -L | grep 53
sudo ufw status | grep 53
Security Considerations
DNS Security
- DNSSEC Support - Enable DNS Security Extensions
- Query Filtering - Filter malicious or unwanted domains
- Rate Limiting - Prevent DNS amplification attacks
- Access Control - Restrict query sources when appropriate
Network Security
- Firewall Rules - Limit DNS port access to necessary sources
- TLS Encryption - Use DNS over TLS for sensitive environments
- Monitoring - Monitor for unusual query patterns
- Logging - Comprehensive query and error logging
Operational Security
- Regular Updates - Keep CoreDNS updated to latest version
- Configuration Validation - Validate configuration changes
- Backup - Regular backup of zone files and configuration
- Access Control - Limit administrative access
Zone Security
- Zone Transfer - Secure zone transfer configuration
- Dynamic Updates - Secure dynamic DNS updates
- Key Management - Proper DNSSEC key management
- Audit Trail - Maintain audit logs for zone changes
Performance Optimization
Query Performance
- Cache Configuration - Optimize cache size and TTL values
- Upstream Selection - Choose fast, reliable upstream servers
- Load Balancing - Distribute queries across multiple upstreams
- Query Optimization - Minimize query response times
System Performance
- Memory Allocation - Allocate sufficient memory for cache
- CPU Optimization - Use appropriate number of worker threads
- Storage Performance - Use fast storage for zone files
- Network Optimization - Optimize network buffer sizes
Monitoring Optimization
- Selective Logging - Log only necessary information
- Metric Collection - Monitor key performance indicators
- Alert Configuration - Set up appropriate alerting thresholds
- Resource Monitoring - Monitor system resource usage
Integration Examples
Prometheus Monitoring
# Corefile configuration for metrics
. {
prometheus localhost:9153
errors
log
cache 30
forward . 8.8.8.8 8.8.4.4
}
Kubernetes Service Discovery
# Kubernetes CoreDNS configuration
apiVersion: v1
kind: ConfigMap
metadata:
name: coredns
namespace: kube-system
data:
Corefile: |
.:53 {
errors
health {
lameduck 5s
}
ready
kubernetes cluster.local in-addr.arpa ip6.arpa {
pods insecure
fallthrough in-addr.arpa ip6.arpa
ttl 30
}
prometheus :9153
forward . /etc/resolv.conf
cache 30
loop
reload
loadbalance
}
Etcd Backend Integration
# Corefile with etcd backend
example.com {
etcd {
stubzones
path /coredns
endpoint http://localhost:2379
}
cache 160
loadbalance
prometheus
errors
log
}
Resources
- Official Documentation: coredns.io
- GitHub Repository: coredns/coredns
- Plugin Documentation: coredns.io/plugins
- Community: coredns.slack.com
- CNCF Project: cncf.io/projects/coredns