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xds: Allow child of cluster_impl LB to change (1.54.x backport) #10103

Merged
merged 1 commit into from
Apr 25, 2023
Merged

xds: Allow child of cluster_impl LB to change (1.54.x backport) #10103

merged 1 commit into from
Apr 25, 2023

Commits on Apr 25, 2023

  1. xds: Allow child of cluster_impl LB to change (grpc#10091) 

    Under normal conditions the child LB of `ClusterImplLoadBalancer` does
not fluctuate, based on the field used to configure load balancing in
the xDS `Cluster` proto it is either:

1. `WrrLocalityLoadBalancer` if the newer `load_balancing_policy` field
   is used
2. `WeightedTargetLoadBalancer` if the legacy `lb_policy` field is used

`ClusterImplLoadBalancer` currently assumes that this child does not
change and so does not change the child LB when the name resolver sends an
update. If the control plane does switch to using a different field for
LB config, that update will have an LB config meant for the other child
LB type. This will result in a ClassCastException and a channel panic.

To address this, `ClusterImplLoadBalancer` will now use
`GracefulSwitchLoadBalancer` and makes sure if the child policy changes
the correct LB implementation is switched to.
    @temawi
    temawi committed Apr 25, 2023
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