Fix excluding of nodes from NetLBs for last node in zone

[anyush]

If no nodes for certain zone were provided to Sync, then all existing ones are removed.

Issue: #2724

[k8s-ci-robot]

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[mmamczur]

/ok-to-test

[mmamczur]

I'm not sure if this would work. zones and nodes actually come from the same place

check out what ZoneGetter.ListZones() does. It lists nodes and extracts zones from them

so if there is no node in zone X then it won't even be in the result from ListZones

[anyush]

@mmamczur That's true (internally ListZones() just uses ListNodes()), but there is used zonegetter.AllNodesFilter which return all nodes including ones with node.kubernetes.io/exclude-from-external-load-balancers=true label (nodes which provided to manager.Sync() are filtered using zonegetter.CandidateNodesFilter).

Only exception are nodes outside of default subnet if such option (ZoneGetter.onlyIncludeDefaultSubnetNodes) enabled, but I think there should be no problem with this.

Should mention: I've tested manually (create regional cluster with 1 node per zone -> create NetLB with subsetting enabled -> label node, so it should be removed (no other nodes in same zone, so none passed to Sync for this zone) -> wait for next Sync() execution - if I'm not wrong ~15m -> check if node removed from IG) and node was successfully removed.

[mmamczur]

ok that sounds good then

[mmamczur]

/hold

[mmamczur]

/unhold

[mmamczur]

/lgtm

[k8s-ci-robot]

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This pull-request has been approved by: anyush, mmamczur

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