This guide shows you how to back up the database of an on-prem Omni instance. Omni uses etcd as its database. There are 2 operating modes for etcd: embedded and external. When Omni is run with --etcd-embedded=true flag, it will configure the embedded etcd server to listen the addresses specified by the --etcd-endpoints flag (http://localhost:2379 by default). In the same host where Omni is running (in Docker, --network=host needs to be used), you can use the etcdctl command to back up the database: 
etcdctl --endpoints http://localhost:2379 snapshot save snapshot.db
The command will save the snapshot of the database to the snapshot.db file. It is recommended to periodically (e.g. with a cron job) take snapshots and store them in a safe location, like an S3 bucket. NOTE: When --etcd-embedded is set to false, the database is external and not managed by Omni. However, it still needs to be regularly backed up. For more info, see etcd disaster recovery.