Ceph

The federated architecture link is broken (404 error) on doc/master/radosgw.

There's no section on federated architecture for versions above Jewel. If my understanding is correct, multisite configurations
replace the federated architecture terminology.

OLD TERMINOLOGY:

A federated Ceph Object Gateway configuration means that you run a Ceph Object Storage service in a geographically distributed manner for fault tolerance and failover.

When you deploy a Ceph Object Store service that spans geographical locales, 
configuring Ceph Object Gateway regions and metadata synchronization agents enables the service to maintain a global namespace, 
even though Ceph Object Gateway instances run in different geographic locales and potentially on different Ceph Storage Clusters.

https://access.redhat.com/documentation/en-us/red_hat_ceph_storage/1.3/html/object_gateway_guide_for_red_hat_enterprise_linux/federated_object_gateway

NEW TERMINOLOGY:

Multi-zone-group: Formerly called ‘regions’, Ceph Object Gateway can also support multiple zone groups, each zone group with one or more zones. 
Objects stored to zones in one zone group within the same realm as another zone group will share a global object namespace, 
ensuring unique object IDs across zone groups and zones.

The Ceph Object Gateway supports multi-site deployments and a global namespace by using the notion of zone groups. 
Formerly called a region in Infernalis, a zone group defines the geographic location of one or more Ceph Object Gateway instances within one or more zones.

http://docs.ceph.com/docs/master/radosgw/multisite/

In my eyes, if I wanted to create a fault-tolerant Ceph object store (radosgw), I would create two Ceph storage clusters and distribute them geographically (each cluster would be in a zone).
The two zones would then be in a multi-zone group (formerly region). One would be a primary object store, the other would be a secondary.
Being that the primary and secondary stores are in the same zone group, the data should replicate across the two object stores (sharing global namespace).
If the primary would fail, the secondary could take its place.

Like this: http://docs.ceph.com/docs/master/radosgw/multisite/#configure-secondary-zones