Remediating nodes with Node Health Checks

You can use the Node Health Check Operator to identify unhealthy nodes. The Operator uses the Self Node Remediation Operator to remediate the unhealthy nodes.

Additional resources

Remediating nodes with the Self Node Remediation Operator

About the Node Health Check Operator

The Node Health Check Operator detects the health of the nodes in a cluster. The NodeHealthCheck controller creates the NodeHealthCheck custom resource (CR), which defines a set of criteria and thresholds to determine the health of a node.

The Node Health Check Operator also installs the Self Node Remediation Operator as a default remediation provider.

When the Node Health Check Operator detects an unhealthy node, it creates a remediation CR that triggers the remediation provider. For example, the controller creates the SelfNodeRemediation CR, which triggers the Self Node Remediation Operator to remediate the unhealthy node.

The NodeHealthCheck CR resembles the following YAML file:

  1. apiVersion: remediation.medik8s.io/v1alpha1
  2. kind: NodeHealthCheck
  3. metadata:
  4.   name: nodehealthcheck-sample
  5. spec:
  6.   minHealthy: 51% (1)
  7.   pauseRequests: (2)
  8.     - <pause-test-cluster>
  9.   remediationTemplate: (3)
  10.     apiVersion: self-node-remediation.medik8s.io/v1alpha1
  11.     name: self-node-remediation-resource-deletion-template
  12.     namespace: openshift-operators
  13.     kind: SelfNodeRemediationTemplate
  14.   selector: (4)
  15.     matchExpressions:
  16.       - key: node-role.kubernetes.io/worker
  17.         operator: Exists
  18.   unhealthyConditions: (5)
  19.     - type: Ready
  20.       status: "False"
  21.       duration: 300s (6)
  22.     - type: Ready
  23.       status: Unknown
  24.       duration: 300s (6)
1Specifies the amount of healthy nodes(in percentage or number) required for a remediation provider to concurrently remediate nodes in the targeted pool. If the number of healthy nodes equals to or exceeds the limit set by minHealthy, remediation occurs. The default value is 51%.
2Prevents any new remediation from starting, while allowing any ongoing remediations to persist. The default value is empty. However, you can enter an array of strings that identify the cause of pausing the remediation. For example, pause-test-cluster.

During the upgrade process, nodes in the cluster might become temporarily unavailable and get identified as unhealthy. In the case of worker nodes, when the Operator detects that the cluster is upgrading, it stops remediating new unhealthy nodes to prevent such nodes from rebooting.

3Specifies a remediation template from the remediation provider. For example, from the Self Node Remediation Operator.
4Specifies a selector that matches labels or expressions that you want to check. The default value is empty, which selects all nodes.
5Specifies a list of the conditions that determine whether a node is considered unhealthy.
6Specifies the timeout duration for a node condition. If a condition is met for the duration of the timeout, the node will be remediated. Long timeouts can result in long periods of downtime for a workload on an unhealthy node.

Understanding the Node Health Check Operator workflow

When a node is identified as unhealthy, the Node Health Check Operator checks how many other nodes are unhealthy. If the number of healthy nodes exceeds the amount that is specified in the minHealthy field of the NodeHealthCheck CR, the controller creates a remediation CR from the details that are provided in the external remediation template by the remediation provider. After remediation, the kubelet updates the node’s health status.

When the node turns healthy, the controller deletes the external remediation template.

About how node health checks prevent conflicts with machine health checks

When both, node health checks and machine health checks are deployed, the node health check avoids conflict with the machine health check.

OKD deploys machine-api-termination-handler as the default MachineHealthCheck resource.

The following list summarizes the system behavior when node health checks and machine health checks are deployed:

  • If only the default machine health check exists, the node health check continues to identify unhealthy nodes. However, the node health check ignores unhealthy nodes in a Terminating state. The default machine health check handles the unhealthy nodes with a Terminating state.

    Example log message

    1. INFO MHCChecker    ignoring unhealthy Node, it is terminating and will be handled by MHC    {"NodeName": "node-1.example.com"}

  • If the default machine health check is modified (for example, the unhealthyConditions is Ready), or if additional machine health checks are created, the node health check is disabled.

    Example log message

    1. INFO controllers.NodeHealthCheck disabling NHC in order to avoid conflict with custom MHCs configured in the cluster {"NodeHealthCheck": "/nhc-worker-default"}

  • When, again, only the default machine health check exists, the node health check is re-enabled.

    Example log message

    1. INFO controllers.NodeHealthCheck re-enabling NHC, no conflicting MHC configured in the cluster {"NodeHealthCheck": "/nhc-worker-default"}

Control plane fencing

In earlier releases, you could enable Self Node Remediation and Node Health Check on worker nodes. In the event of node failure, you can now also follow remediation strategies on control plane nodes.

Do not use the same NodeHealthCheck CR for worker nodes and control plane nodes. Grouping worker nodes and control plane nodes together can result in incorrect evaluation of the minimum healthy node count, and cause unexpected or missing remediations. This is because of the way the Node Health Check Operator handles control plane nodes. You should group the control plane nodes in their own group and the worker nodes in their own group. If required, you can also create multiple groups of worker nodes.

Considerations for remediation strategies:

  • Avoid Node Health Check configurations that involve multiple configurations overlapping the same nodes because they can result in unexpected behavior. This suggestion applies to both worker and control plane nodes.

  • The Node Health Check Operator implements a hardcoded limitation of remediating a maximum of one control plane node at a time. Multiple control plane nodes should not be remediated at the same time.

Installing the Node Health Check Operator by using the web console

You can use the OKD web console to install the Node Health Check Operator.

Prerequisites

  • Log in as a user with cluster-admin privileges.

Procedure

  1. In the OKD web console, navigate to Operators → OperatorHub.

  2. Search for the Node Health Check Operator, then click Install.

  3. Keep the default selection of Installation mode and namespace to ensure that the Operator will be installed to the openshift-operators namespace.

  4. Ensure that the Console plug-in is set to Enable.

  5. Click Install.

Verification

To confirm that the installation is successful:

  1. Navigate to the Operators → Installed Operators page.

  2. Check that the Operator is installed in the openshift-operators namespace and that its status is Succeeded.

If the Operator is not installed successfully:

  1. Navigate to the Operators → Installed Operators page and inspect the Status column for any errors or failures.

  2. Navigate to the Workloads → Pods page and check the logs in any pods in the openshift-operators project that are reporting issues.

Installing the Node Health Check Operator by using the CLI

You can use the OpenShift CLI (oc) to install the Node Health Check Operator.

To install the Operator in your own namespace, follow the steps in the procedure.

To install the Operator in the openshift-operators namespace, skip to step 3 of the procedure because the steps to create a new Namespace custom resource (CR) and an OperatorGroup CR are not required.

Prerequisites

  • Install the OpenShift CLI (oc).

  • Log in as a user with cluster-admin privileges.

Procedure

  1. Create a Namespace custom resource (CR) for the Node Health Check Operator:

    1. Define the Namespace CR and save the YAML file, for example, node-health-check-namespace.yaml:

      1. apiVersion: v1
      2. kind: Namespace
      3. metadata:
      4.   name: node-health-check

    2. To create the Namespace CR, run the following command:

      1. $ oc create -f node-health-check-namespace.yaml

  2. Create an OperatorGroup CR:

    1. Define the OperatorGroup CR and save the YAML file, for example, node-health-check-operator-group.yaml:

      1. apiVersion: operators.coreos.com/v1
      2. kind: OperatorGroup
      3. metadata:
      4.   name: node-health-check-operator
      5.   namespace: node-health-check

    2. To create the OperatorGroup CR, run the following command:

      1. $ oc create -f node-health-check-operator-group.yaml

  3. Create a Subscription CR:

    1. Define the Subscription CR and save the YAML file, for example, node-health-check-subscription.yaml:

      1. apiVersion: operators.coreos.com/v1alpha1
      2. kind: Subscription
      3. metadata:
      4.     name: node-health-check-operator
      5.     namespace: node-health-check (1)
      6. spec:
      7.     channel: stable (2)
      8.     installPlanApproval: Manual (3)
      9.     name: node-healthcheck-operator
      10.     source: redhat-operators
      11.     sourceNamespace: openshift-marketplace
      12.     package: node-healthcheck-operator
      1Specify the Namespace where you want to install the Node Health Check Operator. To install the Node Health Check Operator in the openshift-operators namespace, specify openshift-operators in the Subscription CR.
      2Specify the channel name for your subscription. To upgrade to the latest version of the Node Health Check Operator, you must manually change the channel name for your subscription from candidate to stable.
      3Set the approval strategy to Manual in case your specified version is superseded by a later version in the catalog. This plan prevents an automatic upgrade to a later version and requires manual approval before the starting CSV can complete the installation.

    2. To create the Subscription CR, run the following command:

      1. $ oc create -f node-health-check-subscription.yaml

Verification

  1. Verify that the installation succeeded by inspecting the CSV resource:

    1. $ oc get csv -n openshift-operators

    Example output

    1. NAME                              DISPLAY                     VERSION  REPLACES PHASE
    2. node-healthcheck-operator.v0.2.0. Node Health Check Operator  0.2.0             Succeeded

  2. Verify that the Node Health Check Operator is up and running:

    1. $ oc get deploy -n openshift-operators

    Example output

    1. NAME                                           READY   UP-TO-DATE   AVAILABLE   AGE
    2. node-health-check-operator-controller-manager  1/1     1            1           10d

Creating a node health check

Using the web console, you can create a node health check to identify unhealthy nodes and specify the remediation type and strategy to fix them.

Procedure

  1. From the Administrator perspective of the OKD web console, click Compute → NodeHealthChecks → CreateNodeHealthCheck.

  2. Specify whether to configure the node health check using the Form view or the YAML view.

  3. Enter a Name for the node health check. The name must consist of lower case, alphanumeric characters, ‘-‘ or ‘.’, and must start and end with an alphanumeric character.

  4. Specify the Remediator type, and Self node remediation or Other. The Self node remediation option is part of the Self Node Remediation Operator that is installed with the Node Health Check Operator. Selecting Other requires an API version, Kind, Name, and Namespace to be entered, which then points to the remediation template resource of a remediator.

  5. Make a Nodes selection by specifying the labels of the nodes you want to remediate. The selection matches labels that you want to check. If more than one label is specified, the nodes must contain each label. The default value is empty, which selects both worker and control-plane nodes.

    When creating a node health check with the Self Node Remediation Operator, you must select either node-role.kubernetes.io/worker or node-role.kubernetes.io/control-plane as the value.

  6. Specify the minimum number of healthy nodes, using either a percentage or a number, required for a NodeHealthCheck to remediate nodes in the targeted pool. If the number of healthy nodes equals to or exceeds the limit set by Min healthy, remediation occurs. The default value is 51%.

  7. Specify a list of Unhealthy conditions that if a node meets determines whether the node is considered unhealthy, and requires remediation. You can specify the Type, Status and Duration. You can also create your own custom type.

  8. Click Create to create the node health check.

Verification

  • Navigate to the Compute → NodeHealthCheck page and verify that the corresponding node health check is listed, and their status displayed. Once created, node health checks can be paused, modified, and deleted.

Gathering data about the Node Health Check Operator

To collect debugging information about the Node Health Check Operator, use the must-gather tool. For information about the must-gather image for the Node Health Check Operator, see Gathering data about specific features.

Additional resources