Some etcd configurations (such as that provided by compose.io) place the
etcd cluster behind multiple load balancers or proxies. In this
configuration, calling Sync (or AutoSync) on the etcd client will
replace the load balancer addresses with the underlying etcd server
address.
This will cause the etcd client to bypass the load balancers, and may
cause the connection to fail completely if the etcd servers are
protected by a firewall.
This patch provides a "sync" option for the etcd backend, which defaults
to the current behavior, but which can be used to turn off of sync.
This corresponds to etcdctl's --no-sync option.
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