feat: migrate Traefik Ingress to Kubernetes Gateway API (HTTPRoute)

[ixxeL2097]

Overview

Migrate from the legacy Kubernetes Ingress API to the Gateway API (HTTPRoute, GRPCRoute, Gateway CRDs), the future-standard networking API that Traefik already supports.

Why

The Ingress API is feature-frozen. Gateway API is the official successor with:

• Standardized routing across vendors (no more traefik.ingress.kubernetes.io/ annotations)
• GRPCRoute for native gRPC routing without workarounds
• HTTPRoute filters for request/response manipulation
• Per-route timeout, retry, and header policies
• Split traffic / canary deployments at the routing level
• Already supported by Traefik v3+

Migration path

# Before (Ingress)
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    traefik.ingress.kubernetes.io/router.entrypoints: websecure
    traefik.ingress.kubernetes.io/router.middlewares: traefik-authentik@kubernetescrd
spec:
  rules:
    - host: app.fredcorp.com
      http:
        paths:
          - path: /
            backend:
              service:
                name: app
                port:
                  number: 80

# After (HTTPRoute)
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: app
spec:
  parentRefs:
    - name: traefik-gateway
      namespace: traefik
  hostnames:
    - app.fredcorp.com
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /
      backendRefs:
        - name: app
          port: 80

Phases

1. Enable Gateway API CRDs and Traefik Gateway provider
2. Create Gateway resources (internal + external)
3. Migrate apps one by one (non-breaking alongside existing Ingress)
4. Remove legacy Ingress resources

Notes

• Compatible with existing cert-manager (supports Gateway as a cert target)
• Compatible with external-dns (supports HTTPRoute as a source)
• Enables auto-discovery in Gatus (see feat: add Gatus for uptime monitoring with auto-discovery #1486)

Reference

• Inspired by szinn/k8s-homelab Envoy Gateway setup
• Traefik Gateway API docs: https://doc.traefik.io/traefik/routing/providers/kubernetes-gateway/