Swift has a feature where all the contents of a container
can be mirrored to another container through background syn-
chronization. Swift cluster operators configure their clus-
ter 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-con-
tainer-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.