MultiCIDRServiceAllocator implements a new ClusterIP allocator based on
IPAddress object to solve the problems and limitations caused by
existing bitmap allocators.
However, during the rollout of new versions, deployments need to support
a skew of one version between kube-apiservers. To avoid the possible
problem where there are multiple Services requests on the skewed
apiservers and that both allocate the same IP to different Services,
the new allocator will implement a dual-write strategy under the
feature gate DisableAllocatorDualWrite.
After the MultiCIDRServiceAllocator is GA, the DisableAllocatorDualWrite
can be enabled safely as all apiservers will run with the new
allocators. The graduation of DisableAllocatorDualWrite can also
be used to clean up the opaque API object that contains the old bitmaps.
If MultiCIDRServiceAllocator is enabled and DisableAllocatorDualWrite is disable
and is a new environment, there is no bitmap object created, hence, the
apiserver will initialize it to be able to write on it.
