Failover in this doc cannot work as expected when backend-level filter is applied.
After simulating the active app failure, Envoy continues sending requests to it

In the released v1.3.0, I observed that failover depends on a "BIG"(rule-level) cluster, with weights for different backends within a rule set in the endpoints.
This implementation make add-header filter at the backend level defective.
I notice this issue has been fixed in #3246. But this disrupts failover.
When I enable backend-level filter, the rule-level cluster is absent, causing the failover to not work in this scenario.

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