Experimental Feature: MachinePool (alpha)

The MachinePool feature provides a way to manage a set of machines by defining a common configuration, number of desired machine replicas etc. similar to MachineDeployment, except MachineSet controllers are responsible for the lifecycle management of the machines for MachineDeployment, whereas in MachinePools, each infrastructure provider has a specific solution for orchestrating these Machines.

Feature gate name: MachinePool

Variable name to enable/disable the feature gate: EXP_MACHINE_POOL

Infrastructure providers can support this feature by implementing their specific MachinePool such as AzureMachinePool.

More details on MachinePool can be found at: MachinePool CAEP

For developer docs on the MachinePool controller, see here.

MachinePools vs MachineDeployments

Although MachinePools provide a similar feature to MachineDeployments, MachinePools do so by leveraging an InfraMachinePool which corresponds 1:1 with a resource like VMSS on Azure or Autoscaling Groups on AWS which we treat as a black box. When a MachinePool is scaled up, the InfraMachinePool scales itself up and populates its provider ID list based on the response from the infrastructure provider. On the other hand, a when a MachineDeployment is scaled up, new Machines are created which then create an individual InfraMachine, which corresponds to a VM in any infrastructure provider.

Creates new instances through a single infrastructure resource like VMSS in Azure or Autoscaling Groups in AWS.Creates new instances by creating new Machines, which create individual VM instances on the infra provider.
Set of instances is orchestrated by the infrastructure provider.Set of instances is orchestrated by Cluster API using a MachineSet.
Each MachinePool corresponds 1:1 with an associated InfraMachinePool.Each MachineDeployment includes a MachineSet, and for each replica, it creates a Machine and InfraMachine.
Each MachinePool requires only a single BootstrapConfig.Each MachineDeployment uses an InfraMachineTemplate and a BootstrapConfigTemplate, and each Machine requires a unique BootstrapConfig.
Maintains a list of instances in the providerIDList field in the MachinePool spec. This list is populated based on the response from the infrastructure provider.Maintains a list of instances through the Machine resources owned by the MachineSet.