// Module included in the following assemblies:
//
// * machine_management/creating_machinesets/creating-machineset-aws.adoc
// * machine_management/creating_machinesets/creating-machineset-azure.adoc
// * machine_management/creating_machinesets/creating-machineset-gcp.adoc
// * machine_management/creating_machinesets/creating-machineset-osp.adoc
// * machine_management/creating_machinesets/creating-machineset-vsphere.adoc

[id="machine-api-overview_{context}"]
= Machine API overview

The Machine API is a combination of primary resources that are based on the
upstream Cluster API project and custom {product-title} resources.

For {product-title} {product-version} clusters, the Machine API performs all node
host provisioning management actions after the cluster installation finishes.
Because of this system, {product-title} {product-version} offers an elastic,
dynamic provisioning method on top of public or private cloud infrastructure.

The two primary resources are:

Machines:: A fundamental unit that describes the host for a Node. A machine has a
providerSpec, which describes the types of compute nodes that are offered for different
cloud platforms. For example, a machine type for a worker node on Amazon Web
Services (AWS) might define a specific machine type and required metadata.
MachineSets:: Groups of machines. MachineSets are to machines as
ReplicaSets are to pods. If you need more machines or must scale them down,
you change the *replicas* field on the MachineSet to meet your compute need.

The following custom resources add more capabilities to your cluster:

MachineAutoscaler:: This resource automatically scales machines in
a cloud. You can set the minimum and maximum scaling boundaries for nodes in a
specified MachineSet, and the MachineAutoscaler maintains that range of nodes.
The MachineAutoscaler object takes effect after a ClusterAutoscaler object
exists. Both ClusterAutoscaler and MachineAutoscaler resources are made
available by the ClusterAutoscalerOperator.

ClusterAutoscaler:: This resource is based on the upstream ClusterAutoscaler
project. In the {product-title} implementation, it is integrated with the
Machine API by extending the MachineSet API. You can set cluster-wide
scaling limits for resources such as cores, nodes, memory, GPU,
and so on. You can set the priority so that the cluster prioritizes pods so that
new nodes are not brought online for less important pods. You can also set the
ScalingPolicy so you can scale up nodes but not scale them down.

MachineHealthCheck:: This resource detects when a machine is unhealthy,
deletes it, and, on supported platforms, makes a new machine.
+
[NOTE]
====
In version {product-version}, MachineHealthChecks is a Technology Preview
feature
====

In {product-title} version 3.11, you could not roll out a multi-zone
architecture easily because the cluster did not manage machine provisioning.
Beginning with {product-title} version 4.1, this process is easier. Each MachineSet is scoped to a
single zone, so the installation program sends out MachineSets across
availability zones on your behalf. And then because your compute is dynamic, and
in the face of a zone failure, you always have a zone for when you must
rebalance your machines. The autoscaler provides best-effort balancing over the
life of a cluster.
