How is an ECS federation created?

How is an ECS federation created?
A . From the first ECS running the primary VDC, create an additional VDC entry for each remote ECS instance
B . Add the remote VDC into the replication group configuration for the primary VDC
C . Create a new federation configuration from any VDC, then add all other VDCs to the configuration
D . Create the remote VDC then merge both the first VDC and the remote VDC into the federation configuration

Answer: B