A Guide to Flexible DNS Configuration

Overview

Custom DNS mode lets you use Go templates to generate DNS entries dynamically, giving you precise control over complex DNS configurations. Specify your desired setup in the dnsTemplates field.

You can use functions from the Slim Sprig library in your templates.

What is Custom DNS Mode?

Custom DNS mode uses Go templates to generate DNS entries. Specify your configuration in the dnsTemplates field.

Available Variables in DNS Templates

• {{.domain}}: The value of spec.domain.
• {{.dnsTarget}}: The effective ingress target, specified by spec.dnsTarget or derived from spec.istioIngressSelector.
• {{.subDomain}}: The subdomain of a CAPTenant or a tenant-agnostic workload.

DNS Record Behavior

• Each template typically produces one DNS record.
• If the name contains {{.subDomain}}, a DNS record is created for each valid subdomain from tenants or service exposures.
• {{.subDomain}} may appear in the target only if it also appears in the name.

Example Configuration

The following example configures Custom DNS mode for a Domain resource:

apiVersion: sme.sap.com/v1alpha1
kind: Domain
metadata:
  namespace: cap-app-01
  name: cap-app-01-primary
spec:
  domain: my.cluster.shoot.url.k8s.example.com
  ingressSelector:
    app: istio-ingressgateway
    istio: ingressgateway
  dnsMode: Custom
  dnsTemplates:
  - name: '*.{{ .domain }}'
    target: '{{ .dnsTarget }}'
  - name: '{{ .subDomain }}.{{ .domain }}'
    target: '{{ .dnsTarget }}'
  - name: '{{ .subDomain }}.myapp.com'
    target: '{{ .subDomain }}.{{ .domain }}'

This configuration applies to both Domain and ClusterDomain resources.