PoC Core DNS with DNSRecord

[maleck13]

What

DNS Operator leverages the kuadarnt DNSRecord CR. It should be possible to create a Kuadrant plugin for core dns that allows core dns to source records from our DNSRecord CR. The goal here is to prove we can integrate DNSRecord with Core DNS, identify any potential issues. If successful the outcome here would be a working PoC with a none load balanced DNSPolicy and issues for follow up work to bring the PoC to a "beta" level.

Prior Art: https://github.com/k8gb-io/coredns-crd-plugin

Done

• Understand what is involved in compiling a plugin into Core DNS
• Proof of Concept plugin that can serve basic DNS (without any geo or weighting applied) using our merged DNSRecord CRD
• Identify how we can debug and see logs from our plugin
• Remaining Work Items defined to bring the PoC to a beta level where it is tested and usable

Remaining A poc that handles:

• Handling CNames
• Handling wildcards
• For multi value dnsnames - return the first one in the list
• Basic docs for getting the POC working

[mikenairn]

POC branch is here https://github.com/Kuadrant/dns-operator/tree/coredns.

It contains a CoreDNS plugin that adds the "kuadrant" directive allowing it be added to the CoreDNS Corefile. The plugin will watch for any DNSRecords being created/updated/deleted in any configured namesapces (default is all) that have a label added that corresponds to the zone name in the Corefile:

Example Corefile:

k.example.com {
   kuadrant
}

Example Record:

apiVersion: kuadrant.io/v1alpha1
kind: DNSRecord
metadata:
  name: api-k-example-com
  labels:
    kuadrant.io/zone-name: k.example.com
spec:
  rootHost: api.k.example.com
  endpoints:
    - dnsName: rapi.k.example.com
      recordTTL: 60
      recordType: A
      targets:
        - 1.1.1.1
  providerRef:
    name: dns-provider-credentials-coredns

Example response:

dig @172.18.0.16 api.k.example.com A +short
1.1.1.1

The plugin makes use of the CoreDNS file plugin to do much of the heavy lifting in providing us with a functioning DNS Server, but some modifications were required https://github.com/mikenairn/coredns/tree/add_rrresolver

The plugin also handles recursively resolving CNAMES, so we can get a response we would expect from a dns server when working with our loadbalanced (geo/weighted) records:

dig @172.18.0.16 api.k.example.com A +short
klb.api.k.example.com.
geo-eu.klb.api.k.example.com.
cluster2.klb.api.k.example.com.
127.0.0.2