docs: How to achieve Backend failover?

[ferdinandosimonetti]

Description:
I'd like to implement failover in case of unhealty backend workload for an HTTPRoute.
Scenario:

• two workloads (workload4 and workload2) with their respective Services (workload4 and workload2)
• during normal operations, 100% of the requests coming in through the HTTPRoute should be routed to workload4
• if workload4's Pods fail (or are not present) for whatever reason, then 100% of requests should be routed to workload2

I'm using v0.0.0-latest Helm Chart version and I've set config.envoyGateway.extensionApis.enableBackend=true

I tried this HTTPRoute

---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: tobackend
  namespace: default
spec:
  parentRefs:
    - name: test-fsmn-xyz
      sectionName: https
  hostnames:
    - "test0.fsmn.xyz"
  rules:
    - backendRefs:
        - group: gateway.envoyproxy.io
          kind: Backend
          name: workload4
        - group: gateway.envoyproxy.io
          kind: Backend
          name: workload2
      matches:
        - path:
            type: PathPrefix
            value: /tobackend

And these Backends

---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: Backend
metadata:
  name: workload4
  namespace: default
spec:
  endpoints:
    - fqdn:
        hostname: workload4.default.svc.cluster.local
        port: 80

---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: Backend
metadata:
  name: workload2
  namespace: default
spec:
  fallback: True
  endpoints:
    - fqdn:
        hostname: workload2.default.svc.cluster.local
        port: 3000

But, as if I set workload4's Pods to fail, I keep getting 503 status replies, instead of failing over to workload2's Pods
I guess I'm missing something important, here.
Thanks in advance!

Relevant Links:
Enable Backend

[guydc]

You should also let envoy know how to determine that a certain backend is unhealthy for the failover to kick-in. You can achieve this using either Active or Passive healthchecks in BackendTrafficPolicy applied to the tobackend route:

• https://gateway.envoyproxy.io/latest/api/extension_types/#activehealthcheck
• https://gateway.envoyproxy.io/latest/api/extension_types/#passivehealthcheck