Because Nomad operates at a regional level, federation is part of Nomad core. Federation enables users to submit jobs or interact with the HTTP API targeting any region, from any server, even if that server resides in a different region.
Federating multiple Nomad clusters requires network connectivity between the clusters. Servers in each cluster must be able to communicate over RPC and Serf. Federated clusters are expected to communicate over WANs, so they do not need the same low latency as servers within a region.
Once Nomad servers are able to connect, federating is as simple as joining the servers. From any server in one region, issue a join command to a server in a remote region:
nomad server join 188.8.131.52:4648
Note that only one join command is required per region. Servers across regions discover other servers in the cluster via the gossip protocol and hence it's enough to join just one known server.
If bootstrapped via Consul and the Consul clusters in the Nomad regions are federated, then federation occurs automatically.