This change builds on top of #14436 to ensure minimum downtime during egress ProxyGroup update rollouts:
- adds a readiness gate for ProxyGroup replicas that prevents kubelet from marking
the replica Pod as ready before a corresponding readiness condition has been added
to the Pod
- adds a reconciler that reconciles egress ProxyGroup Pods and, for each that is not ready,
if cluster traffic for relevant egress endpoints is routed via this Pod- if so add the
readiness condition to allow kubelet to mark the Pod as ready.
During the sequenced StatefulSet update rollouts kubelet does not restart
a Pod before the previous replica has been updated and marked as ready, so
ensuring that a replica is not marked as ready allows to avoid a temporary
post-update situation where all replicas have been restarted, but none of the
new ones are yet set up as an endpoint for the egress service, so cluster traffic is dropped.
Updates tailscale/tailscale#14326
Signed-off-by: Irbe Krumina <irbe@tailscale.com>
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