Every other control needs this box. It is ephemeral and holds a lease — a running op keeps renewing it, so a long job is never reaped mid-flight. Start brings up the box and then has it build the cluster: from the barman archive if one holds a base backup, from scratch if none does. If a cluster is already ACTIVE it is left alone.
Type the cluster name to arm. These have no undo.
Four phases. Each waits for the one before it, and phase 1 failing is a stop, not a retry.
Prefer the serverName whose last WAL is NEWEST — after a teardown that is the one phase 2's pre-teardown base backup wrote to.
select a run