Setting up a working Leader/Follower replication requires at least two ArangoDB instances:
Leader: this is the instance where all data-modification operations should be directed to.
Follower: this is the instance that replicates, in an asynchronous way, the data from the Leader. For the replication to happen, a replication applier has to be started on the Follower. The replication applier will fetch data from the Leader’s write-ahead log and apply its operations locally. One or more Followers can replicate from the same Leader.
Generally, one deploys the Leader on a machine and each Follower on an additional, separate, machine (one per Follower). In case the Leader and the Followers are running on the same machine (tests only), please make sure you use different ports (and data directories) for the Leader and the Followers.
Please install the Leader and the Followers as they were, separate, single instances. There are no specific differences, at this stage, between a Leader a Follower and a single instance.
Once the ArangoDB Leader and Followers have been deployed, the replication has to be started on each of the available Followers. This can be done at database level, or globally.
For further information on how to set up the replication in Leader/Follower environment, please refer to this Section.