Dynamic Kubernetes Ingress host with Kustomize

ingress.yaml

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ingress-resource
  annotations:
    kubernetes.io/ingress.class: "nginx"
spec:
  rules:
    - host: foo.example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: webapp-service
                port:
                  number: 80

kustomization.yaml

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

commonLabels:
  pull-request: this_will_be_the_new_url

resources:
  - ingress.yaml

replacements:
  - source:
      kind: Ingress
      fieldPath: metadata.labels.pull-request
    targets:
      - select:
          kind: Ingress
        fieldPaths:
          - spec.rules.0.host
        options:
          delimiter: "."

kustomize-output.shell

❯ kubectl kustomize .

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    kubernetes.io/ingress.class: nginx
  labels:
    pull-request: this_will_be_the_new_url
  name: ingress-resource
spec:
  rules:
  - host: this_will_be_the_new_url.example.com
    http:
      paths:
      - backend:
          service:
            name: webapp-service
            port:
              number: 80
        path: /
        pathType: Prefix