registry gstg cluster b is not receiving traffic

While executing load tests we noticed registry cluster b in gstg to not receive the same amount of traffic as the other 2 clusters.

Thanos

• investigate the reason
• fix it

Investigation findings

Confirmed as expected - #2044 (comment 698392643)

In order to not have cross zonal traffic (which costs us more), we only send traffic to the gke backend in the same zone (with the others marked as backup). In this case as there is no haproxy in us-east1-b, it will be the backup in both haproxy nodes, but neither node will have it as a primary backend.

Only real way to fix this is to either change our haproxy configuration or add a new fe node in us-east1-b. Not sure if either option is worth it.