Blue-green and recreate

The engine starts new instances next to the old ones, or after them for a service with a disk.

Blue-green, the default: the old instances continue to answer while the new instances start.

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Strategy	For	What the engine does
Blue-green (default)	A service with no disk	It starts the new instances next to the old instances. The old instances answer until the switch.
Recreate	A service with a disk	It stops the old instance first. Then it starts the new instance.

Why recreate exists

Two containers cannot share a disk safely. Thus a service with a disk has no zero downtime deploy.

For the user view, see Scaling.

Start the instances

After the build, the engine starts the wanted number of instances from the snapshot.

The health check

The engine tests each new instance each second until it passes or the timeout ends.