lhci-external-ingress.yaml

apiVersion: traefik.containo.us/v1alpha1
kind: IngressRoute
metadata:
  name: lhci-forwarder
spec:
  entryPoints:
    - web
    - websecure
  routes:
  - kind: Rule
    match: Host(`lighthouse.cony.line.dev`)
    services:
    - kind: Service
      name: lhci-external-svc
      passHostHeader: false
      port: https
      scheme: https
  # tls: {}

---
apiVersion: v1
kind: Service
metadata:
  name: lhci-external-svc
spec:
  externalName: lhci-farm-dev.linecorp.com
  type: ExternalName
  ports:
    - name: https
      port: 443

LGTM