ArangoDB v3.4 reached End of Life (EOL) and is no longer supported.
This documentation is outdated. Please see the most recent version here: Latest Docs
ArangoDB has no built-in limitations to horizontal scalability. The central resilient Agency will easily sustain hundreds of DBservers and Coordinators, and the usual database operations work completely decentrally and do not require assistance of the Agency.
Likewise, the supervision process in the Agency can easily deal with lots of servers, since all its activities are not performance critical.
Obviously, an ArangoDB Cluster is limited by the available resources of CPU, memory, disk and network bandwidth and latency.