sigs.k8s.io/cluster-api@v1.7.1/docs/book/src/tasks/experimental-features/machineset-preflight-checks.md (about)

     1  # Experimental Feature: MachineSetPreflightChecks (alpha)
     2  
     3  The `MachineSetPreflightChecks` feature can provide additional safety while creating new Machines and remediating existing unhealthy Machines of a MachineSet.
     4  
     5  When a MachineSet creates machines under certain circumstances, the operation fails or leads to a new machine that will be deleted and recreated in a short timeframe,
     6  leading to unwanted Machine churn. Some of these circumstances include, but not limited to, creating a new Machine when Kubernetes version skew could be violated or 
     7  joining a Machine when the Control Plane is upgrading leading to failure because of mixed kube-apiserver version or due to the cluster load balancer delays in adapting
     8  to the changes.
     9  
    10  Enabling `MachineSetPreflightChecks` provides safety in such circumstances by making sure that a Machine is only created when it is safe to do so.
    11  
    12  
    13  **Feature gate name**: `MachineSetPreflightChecks`
    14  
    15  **Variable name to enable/disable the feature gate**: `EXP_MACHINE_SET_PREFLIGHT_CHECKS`
    16  
    17  ## Supported PreflightChecks
    18  
    19  ### `ControlPlaneIsStable`
    20  
    21  * This preflight check ensures that the ControlPlane is currently stable i.e. the ControlPlane is currently neither provisioning nor upgrading.   
    22  * This preflight check is only performed if:
    23    * The Cluster uses a ControlPlane provider.
    24    * ControlPlane version is defined (`ControlPlane.spec.version` is set).
    25  
    26  ### `KubernetesVersionSkew`
    27  
    28  * This preflight check ensures that the MachineSet and the ControlPlane conform to the [Kubernetes version skew](https://kubernetes.io/releases/version-skew-policy/#kubelet).
    29  * This preflight check is only performed if:
    30      * The Cluster uses a ControlPlane provider.
    31      * ControlPlane version is defined (`ControlPlane.spec.version` is set).
    32      * MachineSet version is defined (`MachineSet.spec.template.spec.version` is set).
    33  
    34  ### `KubeadmVersionSkew`
    35  
    36  * This preflight check ensures that the MachineSet and the ControlPlane conform to the [kubeadm version skew](https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/create-cluster-kubeadm/#kubeadm-s-skew-against-kubeadm).
    37  * This preflight check is only performed if:
    38    * The Cluster uses a ControlPlane provider.
    39    * ControlPlane version is defined (`ControlPlane.spec.version` is set).
    40    * MachineSet version is defined (`MachineSet.spec.template.spec.version` is set).
    41    * MachineSet uses the `Kubeadm` Bootstrap provider.
    42  
    43  ## Opting out of PreflightChecks
    44  
    45  Once the feature flag is enabled the preflight checks are enabled for all the MachineSets including new and existing MachineSets.
    46  It is possible to opt-out of one or all of the preflight checks on a per MachineSet basis by specifying a comma-separated list of the preflight checks on the 
    47  `machineset.cluster.x-k8s.io/skip-preflight-checks` annotation on the MachineSet.  
    48  
    49  Examples: 
    50  * To opt out of all the preflight checks set the `machineset.cluster.x-k8s.io/skip-preflight-checks: All` annotation.
    51  * To opt out of the `ControlPlaneIsStable` preflight check set the `machineset.cluster.x-k8s.io/skip-preflight-checks: ControlPlaneIsStable` annotation.
    52  * To opt out of multiple preflight checks set the `machineset.cluster.x-k8s.io/skip-preflight-checks: ControlPlaneIsStable,KubernetesVersionSkew` annotation.
    53  
    54  <aside class="note">
    55  
    56  <h1>Pro-tip: Set annotation through MachineDeployment</h1>
    57  
    58  Because of the [metadata propagation](../../developer/architecture/controllers/metadata-propagation.md#machinedeployment) rules in Cluster API you can set the `machineset.cluster.x-k8s.io/skip-preflight-checks` annotation 
    59  on a MachineDeployment and it will be automatically set on the MachineSets of that MachineDeployment, including any new MachineSets created when the MachineDeployment performs a rollout.
    60  
    61  </aside>
    62  
    63