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Remediating nodes with the Self Node Remediation Operator

About the Self Node Remediation Operator

The Self Node Remediation Operator runs on the cluster nodes and reboots nodes that are identified as unhealthy. The Operator uses the MachineHealthCheck or NodeHealthCheck controller to detect the health of a node in the cluster. When a node is identified as unhealthy, the MachineHealthCheck or the NodeHealthCheck resource creates the SelfNodeRemediation custom resource (CR), which triggers the Self Node Remediation Operator.

The SelfNodeRemediation CR resembles the following YAML file:

apiVersion: self-node-remediation.medik8s.io/v1alpha1
kind: SelfNodeRemediation
metadata:
  name: selfnoderemediation-sample
  namespace: openshift-operators
spec:
status:
  lastError: <last_error_message> (1)
1 Displays the last error that occurred during remediation. When remediation succeeds or if no errors occur, the field is left empty.

The Self Node Remediation Operator minimizes downtime for stateful applications and restores compute capacity if transient failures occur. You can use this Operator regardless of the management interface, such as IPMI or an API to provision a node, and regardless of the cluster installation type, such as installer-provisioned infrastructure or user-provisioned infrastructure.

Understanding the Self Node Remediation Operator configuration

The Self Node Remediation Operator creates the SelfNodeRemediationConfig CR with the name self-node-remediation-config. The CR is created in the namespace of the Self Node Remediation Operator.

A change in the SelfNodeRemediationConfig CR re-creates the Self Node Remediation daemon set.

The SelfNodeRemediationConfig CR resembles the following YAML file:

apiVersion: self-node-remediation.medik8s.io/v1alpha1
kind: SelfNodeRemediationConfig
metadata:
  name: self-node-remediation-config
  namespace: openshift-operators
spec:
  safeTimeToAssumeNodeRebootedSeconds: 180 (1)
  watchdogFilePath: /dev/watchdog (2)
  isSoftwareRebootEnabled: true (3)
  apiServerTimeout: 15s (4)
  apiCheckInterval: 5s (5)
  maxApiErrorThreshold: 3 (6)
  peerApiServerTimeout: 5s (7)
  peerDialTimeout: 5s (8)
  peerRequestTimeout: 5s (9)
  peerUpdateInterval: 15m (10)
1 Specify the timeout duration for the surviving peer, after which the Operator can assume that an unhealthy node has been rebooted. The Operator automatically calculates the lower limit for this value. However, if different nodes have different watchdog timeouts, you must change this value to a higher value.
2 Specify the file path of the watchdog device in the nodes. If you enter an incorrect path to the watchdog device, the Self Node Remediation Operator automatically detects the softdog device path.

If a watchdog device is unavailable, the SelfNodeRemediationConfig CR uses a software reboot.
3 Specify if you want to enable software reboot of the unhealthy nodes. By default, the value of isSoftwareRebootEnabled is set to true. To disable the software reboot, set the parameter value to false.
4 Specify the timeout duration to check connectivity with each API server. When this duration elapses, the Operator starts remediation. The timeout duration must be more than or equal to 10 milliseconds.
5 Specify the frequency to check connectivity with each API server. The timeout duration must be more than or equal to 1 second.
6 Specify a threshold value. After reaching this threshold, the node starts contacting its peers. The threshold value must be more than or equal to 1 second.
7 Specify the duration of the timeout for the peer to connect the API server. The timeout duration must be more than or equal to 10 milliseconds.
8 Specify the duration of the timeout for establishing connection with the peer. The timeout duration must be more than or equal to 10 milliseconds.
9 Specify the duration of the timeout to get a response from the peer. The timeout duration must be more than or equal to 10 milliseconds.
10 Specify the frequency to update peer information, such as IP address. The timeout duration must be more than or equal to 10 seconds.

You can edit the self-node-remediation-config CR that is created by the Self Node Remediation Operator. However, when you try to create a new CR for the Self Node Remediation Operator, the following message is displayed in the logs:

controllers.SelfNodeRemediationConfig
ignoring selfnoderemediationconfig CRs that are not named 'self-node-remediation-config'
or not in the namespace of the operator:
'openshift-operators' {"selfnoderemediationconfig":
"openshift-operators/selfnoderemediationconfig-copy"}

Understanding the Self Node Remediation Template configuration

The Self Node Remediation Operator also creates the SelfNodeRemediationTemplate Custom Resource Definition (CRD). This CRD defines the remediation strategy for the nodes. The following remediation strategies are available:

ResourceDeletion

This remediation strategy removes the pods and associated volume attachments on the node rather than the node object. This strategy helps to recover workloads faster. ResourceDeletion is the default remediation strategy.

NodeDeletion

This remediation strategy removes the node object.

The Self Node Remediation Operator creates the following SelfNodeRemediationTemplate CRs for each strategy:

  • self-node-remediation-resource-deletion-template, which the ResourceDeletion remediation strategy uses

  • self-node-remediation-node-deletion-template, which the NodeDeletion remediation strategy uses

The SelfNodeRemediationTemplate CR resembles the following YAML file:

apiVersion: self-node-remediation.medik8s.io/v1alpha1
kind: SelfNodeRemediationTemplate
metadata:
  creationTimestamp: "2022-03-02T08:02:40Z"
  name: self-node-remediation-<remediation_object>-deletion-template (1)
  namespace: openshift-operators
spec:
  template:
    spec:
      remediationStrategy: <remediation_strategy>  (2)
1 Specifies the type of remediation template based on the remediation strategy. Replace <remediation_object> with either resource or node, for example, self-node-remediation-resource-deletion-template.
2 Specifies the remediation strategy. The remediation strategy can either be ResourceDeletion or NodeDeletion.

About watchdog devices

Watchdog devices can be any of the following:

  • Independently powered hardware devices

  • Hardware devices that share power with the hosts they control

  • Virtual devices implemented in software, or softdog

Hardware watchdog and softdog devices have electronic or software timers, respectively. These watchdog devices are used to ensure that the machine enters a safe state when an error condition is detected. The cluster is required to repeatedly reset the watchdog timer to prove that it is in a healthy state. This timer might elapse due to fault conditions, such as deadlocks, CPU starvation, and loss of network or disk access. If the timer expires, the watchdog device assumes that a fault has occurred and the device triggers a forced reset of the node.

Hardware watchdog devices are more reliable than softdog devices.

Understanding Self Node Remediation Operator behavior with watchdog devices

The Self Node Remediation Operator determines the remediation strategy based on the watchdog devices that are present.

If a hardware watchdog device is configured and available, the Operator uses it for remediation. If a hardware watchdog device is not configured, the Operator enables and uses a softdog device for remediation.

If neither watchdog devices are supported, either by the system or by the configuration, the Operator remediates nodes by using software reboot.

Additional resources

Configuring a watchdog

Installing the Self Node Remediation Operator by using the web console

You can use the OpenShift Container Platform web console to install the Self Node Remediation Operator.

Prerequisites

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

Procedure

  1. In the OpenShift Container Platform web console, navigate to Operators → OperatorHub.

  2. Search for the Self Node Remediation Operator from the list of available Operators, and then click Install.

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

  4. 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 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 self-node-remediation-controller-manager project that are reporting issues.

Installing the Self Node Remediation Operator by using the CLI

You can use the OpenShift CLI (oc) to install the Self Node Remediation Operator.

You can install the Self Node Remediation Operator in your own namespace or in the openshift-operators namespace.

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 Self Node Remediation Operator:

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

      apiVersion: v1
kind: Namespace
metadata:
  name: self-node-remediation

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

      $ oc create -f self-node-remediation-namespace.yaml

  2. Create an OperatorGroup CR:

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

      apiVersion: operators.coreos.com/v1
kind: OperatorGroup
metadata:
  name: self-node-remediation-operator
  namespace: self-node-remediation

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

      $ oc create -f self-node-remediation-operator-group.yaml

  3. Create a Subscription CR:

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

      apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
    name: self-node-remediation-operator
    namespace: self-node-remediation (1)
spec:
    channel: stable
    installPlanApproval: Manual (2)
    name: self-node-remediation-operator
    source: redhat-operators
    sourceNamespace: openshift-marketplace
    package: self-node-remediation
      1 Specify the Namespace where you want to install the Self Node Remediation Operator. To install the Self Node Remediation Operator in the openshift-operators namespace, specify openshift-operators