Documentation

Volumes

Block volumes attach to a machine and survive it. Detach a volume from one machine and attach it to another; deleting the machine does not delete the volume.

Snapshots

A snapshot is a point-in-time copy you can restore from. Take one before an upgrade, not after — a snapshot is only useful if it predates the mistake.

Firewalls

Rules are grouped and applied per machine. Start closed: open the ports the service needs and nothing else. The most common incident on any cloud is a database that was reachable from the internet because a rule was added "temporarily".