CoreDNS

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Overview

• Run it directly to get a managed CoreDNS container with sensible defaults
• Inherit it in your own runnable to seamlessly add a flexible, extensible DNS server to your infrastructure

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What this template manages

• CoreDNS container (coredns/coredns image, configurable tag)
• DNS service on port 53 (UDP)
• Custom CoreDNS configuration (Corefile)
• Plugin-based DNS functionality
• Persistent volume for zone files and configuration

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Quick start (run directly)

1. Load templates

monk load MANIFEST

2. Run CoreDNS with a custom zone domain

monk run coredns/coredns -v zone-domain=example.local

3. Customize configuration (recommended via inheritance)

• Preferred: inherit and override variables as shown below.
• Alternative: fork/clone and edit the variables in coredns/coredns.yaml, then monk load MANIFEST and run.

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Configuration

variables:
  image-tag: "1.11.3"                   # CoreDNS container image tag
  config-dir: "${monk-volume-path}/coredns"  # host path for zone files
  zone-domain: "example.local"          # domain name for your custom zone (required)

• A catch-all zone (.) that forwards queries to upstream DNS servers
• A custom zone configured via zone-domain variable that serves from a zone file
• Logging and error reporting enabled
• 5-second reload interval for zone file changes

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Use by inheritance (recommended for infrastructure)

namespace: myapp
dns-server:
  defines: runnable
  inherits: coredns/coredns
  variables:
    zone-domain:
      value: myapp.local
    image-tag:
      value: 1.11.3
  files:
    zone-file:
      container: coredns
      path: /config/myapp.local.db
      contents: |
        $ORIGIN myapp.local.
        @       3600 IN SOA sns.dns.icann.org. noc.dns.icann.org. (
                                2023010101 ; serial
                                7200       ; refresh
                                3600       ; retry
                                1209600    ; expire
                                3600       ; minimum
                                )
        
        @       IN NS    ns1.myapp.local.
        ns1     IN A     10.0.0.1
        api     IN A     10.0.0.10
        db      IN A     10.0.0.11
        web     IN A     10.0.0.12

namespace: myapp
dns-server:
  defines: runnable
  inherits: coredns/coredns
  variables:
    zone-domain:
      value: myapp.local
  files:
    corefile:
      container: coredns
      path: /etc/coredns/Corefile
      contents: |
        .:53 {
          forward . 1.1.1.1 1.0.0.1
          cache 30
          log
          errors
        }
        
        myapp.local:53 {
          file /config/myapp.local.db {
            reload 5s
          }
          log
          errors
        }

monk run myapp/dns-server

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Ports and connectivity

• Service: dns on UDP port 53
• From other runnables in the same process group, use connection-hostname("\<connection-name>") to resolve the DNS server host.

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Plugins

• forward: Forwarding queries to upstream DNS servers (8.8.8.8, 9.9.9.9)
• file: Serving zone data from files
• log: Query logging
• errors: Error logging

• kubernetes: Service discovery for Kubernetes
• cache: Caching DNS responses
• prometheus: Exporting metrics to Prometheus
• rewrite: Rewriting queries
• etcd: Backend storage in etcd
• loadbalance: Load balancing with random selection

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Persistence and configuration

• Zone files path: ${monk-volume-path}/coredns:/config
• Corefile location: /etc/coredns/Corefile (in container)
• You can place additional zone files in the config path and reference them in your Corefile

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Zone file format

$ORIGIN example.local.
@       3600 IN SOA ns1.example.local. admin.example.local. (
                        2023010101 ; serial
                        7200       ; refresh
                        3600       ; retry
                        1209600    ; expire
                        3600       ; minimum
                        )

@       IN NS    ns1.example.local.
ns1     IN A     192.168.1.1
www     IN A     192.168.1.10
api     IN A     192.168.1.11

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Related templates

• See other templates in this repository for complementary services
• Combine with monitoring tools (prometheus-grafana/) for observability
• Integrate with your application stack as needed

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Troubleshooting

• Ensure port 53 is available and not blocked by another DNS service
• Verify your Corefile configuration is valid (use coredns -conf /etc/coredns/Corefile -validate inside the container)
• Ensure zone files exist in the config directory and have correct permissions
• Check that zone-domain variable is set when running the template
• Check logs:

monk logs -l 500 -f coredns/coredns

• Test DNS resolution:

dig @localhost example.local
dig @localhost api.example.local

• Verify zone file syntax:

# Check if zone file is readable and properly formatted
monk exec coredns/coredns "cat /config/example.local.db"

• If queries are not being answered, ensure the zone file matches the zone-domain variable (e.g., if zone-domain=example.local, the zone file should be named example.local.db)