Swift has a feature where all the contents of a container can be mirrored to another container through
background synchronization. Swift cluster operators configure their cluster to allow/accept sync requests
to/from other clusters, and the user specifies where to sync their container to along with a secret
synchronization key.
The swift-container-sync does the job of sending updates to the remote container. This is done by
scanning the local devices for container databases and checking for x-container-sync-to and x-container-
sync-key metadata values. If they exist, newer rows since the last sync will trigger PUTs or DELETEs to
the other container.