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
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.