Description
Describe the feature request
Hi,
When using the global mesh LocalityLoadBalancerSetting in distribute mode, pilot doesn't set any priority in the generated LocalityLbEndpoints (in https://github.com/istio/istio/blob/master/pilot/pkg/networking/core/v1alpha3/loadbalancer/loadbalancer.go#L80 )
The priorities are only applied when failover is enabled, based on locality.
It would be extremely useful if weighted and prioritised distribution could be applied: this would allow for, for example, cross-AZ traffic to be priority 0, with different weightings per-AZ, but cross-region traffic could be dropped to priority 1, as a failover case. Envoy's docs and APIs say that this is possible, with priorities being checked before weightings.
I think this could be exposed through an additional prioritised setting, e.g.
distribute:
- from: *
to:
"us-west/zone1/*": 49
"us-west/zone2/*": 49
"us-east/*: 2
prioritised: true
where priorities would be determined based on locality, as in the current failover implementation. I don't think there's a need to specify explicit priorities.
or even by allowing both failover and distribute to be specified? I'm not sure of the reasoning behind only allowing one or the other - is there a design doc around that?
Describe alternatives you've considered
I tried using an EnvoyFilter to set priorities for existing LocalityLbEdndpoints but with the JSON merging semantics I was only able to append new endpoints, not modify existing list items.
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