Publishing, fleet readiness, and ACTIVE versions

Publishing is the step that turns a configured function plus capacity provider into running managed capacity and an ACTIVE function version in your account.

For API behaviour, timing, and region-specific details, use Lambda Managed Instances as the product reference.

End-to-end sequence

Step	What you configure	Result
1	Capacity provider — VPC, instance requirements, scaling limits	Placement and fleet bounds for LMI
2	Function with `capacity_provider_config` pointing at that provider	Function is bound to managed capacity (not Shared Lambda infrastructure for execution)
3	Publish a function version	Lambda readies managed instances and execution environments; the version becomes ACTIVE when the fleet is ready

Publishing is a versioned milestone: until the version is ACTIVE, it is not the live target for traffic on that release.

What happens when you publish

Topic	Behaviour
Managed instances	Lambda starts managed instances in your account. By default AWS uses three instances for Availability Zone resiliency and brings up three execution environments before marking the version ACTIVE.
Reuse on busy providers	If the capacity provider already runs other functions, Lambda may host the new version’s environments on existing instances when spare capacity exists, instead of adding instances.

For the three-step overview in narrative form, see Introduction.