Simon Willison’s Weblog

Making Machines Move. Another deep technical dive into Fly.io infrastructure from Thomas Ptacek, this time describing how they can quickly boot up an instance with a persistent volume on a new host (for things like zero-downtime deploys) using a block-level cloning operation, so the new instance gets a volume that becomes accessible instantly, serving proxied blocks of data until the new volume has been completely migrated from the old host.