Merge pull request #7354 from Jont828/mp-md-comparison

📖 Add side-by-side comparison of MachinePools and MachineDeployments in docs

Author: k8s-ci-robot

docs/book/src/tasks/experimental-features/machine-pools.md

@@ -25,3 +25,15 @@ More details on `MachinePool` can be found at:
 [MachinePool CAEP](https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/20190919-machinepool-api.md)
 
 For developer docs on the MachinePool controller, see [here](./../../developer/architecture/controllers/machine-pool.md).
+
+## 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.
+
+| MachinePools                                                                                                                                                        | MachineDeployments                                                                                                                     |
+| ------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------- |
+| 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.                                                   |