Leases prevent multiple applications from requesting the same dataset on different nodes at the same time.
Leases are accessed via the Flocker REST API exposed by the Flocker control service, however most users will interact with leases through the Flocker Plugin for Docker, which will handle requesting leases for you.
After a dataset has been moved to a node, an application can acquire a lease for that dataset. While the lease is active, any other requests for that dataset on a different node will be rejected with an error. When an application no longer requires a dataset it can release the lease.
Leases can be released by any user of the API, so if an application does not release a lease, it can be released manually.
Leases can be configured to expire after a given time. Before that time has passed, a lease can be refreshed with a new expiration time.