In particular, if one sets the “data center ID” database option, the client will prefer to use fdbserver processes with that same data center ID when performing reads: https://apple.github.io/foundationdb/api-python.html#database-options
That parameter is set at fdbserver startup, and it can be set to basically whatever is useful to the administrator (I think probably with some maximum length).
Note that the configuration called
three_datacenter in FDB (which uses, as you might expect, three data centers) is not particularly optimized to minimize WAN traffic, so as a result, it might provide higher latencies than one would expect and throughput can suffer just due to the volume of cross-DC traffic that is done. Region configurations do a better job about being more careful about when data are shipped across the WAN, but they currently only support two datacenters: https://apple.github.io/foundationdb/configuration.html#configuring-regions