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Chapter 3. Using Fence Agents Remediation

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You can use the Fence Agents Remediation Operator to automatically remediate unhealthy nodes, similar to the Self Node Remediation Operator. FAR is designed to run an existing set of upstream fencing agents on environments with a traditional API end-point, for example, IPMI, for power cycling cluster nodes, while their pods are quickly evicted based on the remediation strategy.

3.1. About the Fence Agents Remediation Operator

The Fence Agents Remediation (FAR) Operator uses external tools to fence unhealthy nodes. These tools are a set of fence agents, where each fence agent can be used for different environments to fence a node, and using a traditional Application Programming Interface (API) call that reboots a node. By doing so, FAR can minimize downtime for stateful applications, restores compute capacity if transient failures occur, and increases the availability of workloads.

FAR not only fences a node when it becomes unhealthy, it also tries to remediate the node from being unhealthy to healthy. It adds a taint to evict stateless pods, fences the node with a fence agent, and after a reboot, it completes the remediation with resource deletion to remove any remaining workloads (mostly stateful workloads). Adding the taint and deleting the workloads accelerates the workload rescheduling.

The Operator watches for new or deleted custom resources (CRs) called FenceAgentsRemediation which trigger a fence agent to remediate a node, based on the CR’s name. FAR uses the NodeHealthCheck controller to detect the health of a node in the cluster. When a node is identified as unhealthy, the NodeHealthCheck resource creates the FenceAgentsRemediation CR, based on the FenceAgentsRemediationTemplate CR, which then triggers the Fence Agents Remediation Operator.

FAR uses a fence agent to fence a Kubernetes node. Generally, fencing is the process of taking unresponsive/unhealthy computers into a safe state, and isolating the computer. Fence agent is a software code that uses a management interface to perform fencing, mostly power-based fencing which enables power-cycling, reset, or turning off the computer. An example fence agent is fence_ipmilan which is used for Intelligent Platform Management Interface (IPMI) environments. 

apiVersion: fence-agents-remediation.medik8s.io/v1alpha1
kind: FenceAgentsRemediation
metadata:
  name: node-name 1
  namespace: openshift-workload-availability
spec:
  remediationStrategy: <remediation_strategy> 2
1
The node-name should match the name of the unhealthy cluster node.
2
Specifies the remediation strategy for the nodes. For more information on the remediation strategies available, see the Understanding the Fence Agents Remediation Template configuration topic.

The Operator includes a set of fence agents, that are also available in the Red Hat High Availability Add-On, which use a management interface, such as IPMI or an API, to provision/reboot a node for bare metal servers, virtual machines, and cloud platforms.

3.2. Installing the Fence Agents Remediation Operator by using the web console

You can use the Red Hat OpenShift web console to install the Fence Agents Remediation Operator.

Prerequisites

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

Procedure

  1. In the Red Hat OpenShift web console, navigate to Operators OperatorHub.
  2. Select the Fence Agents Remediation Operator, or FAR, 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-workload-availability 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-workload-availability 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 log of the fence-agents-remediation-controller-manager pod for any reported issues.

3.3. Installing the Fence Agents Remediation Operator by using the CLI

You can use the OpenShift CLI (oc) to install the Fence Agents Remediation Operator.

You can install the Fence Agents Remediation Operator in your own namespace or in the openshift-workload-availability namespace.

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 Fence Agents Remediation Operator:

    1. Define the Namespace CR and save the YAML file, for example, workload-availability-namespace.yaml: 

      apiVersion: v1
kind: Namespace
metadata:
  name: openshift-workload-availability

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

      $ oc create -f workload-availability-namespace.yaml

  2. Create an OperatorGroup CR:

    1. Define the OperatorGroup CR and save the YAML file, for example, workload-availability-operator-group.yaml: 

      apiVersion: operators.coreos.com/v1
kind: OperatorGroup
metadata:
  name: workload-availability-operator-group
  namespace: openshift-workload-availability

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

      $ oc create -f workload-availability-operator-group.yaml

  3. Create a Subscription CR:

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

      apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
    name: fence-agents-remediation-subscription
    namespace: openshift-workload-availability 1
spec:
    channel: stable
    name: fence-agents-remediation
    source: redhat-operators
    sourceNamespace: openshift-marketplace
    package: fence-agents-remediation
      1
      Specify the Namespace where you want to install the Fence Agents Remediation Operator, for example, the openshift-workload-availability outlined earlier in this procedure. You can install the Subscription CR for the Fence Agents Remediation Operator in the openshift-workload-availability namespace where there is already a matching OperatorGroup CR.

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

      $ oc create -f fence-agents-remediation-subscription.yaml

Verification

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

    $ oc get csv -n openshift-workload-availability

    Example output

    NAME                               DISPLAY                          VERSION   REPLACES   PHASE
fence-agents-remediation.v0.4.0      Fence Agents Remediation Operator   0.4.0   fence-agents-remediation.v0.3.0           Succeeded

  2. Verify that the Fence Agents Remediation Operator is up and running: 

    $ oc get deployment -n openshift-workload-availability

    Example output

    NAME                                        READY   UP-TO-DATE   AVAILABLE   AGE
fence-agents-remediation-controller-manager    2/2     2            2           110m

3.4. Configuring the Fence Agents Remediation Operator

You can use the Fence Agents Remediation Operator to create the FenceAgentsRemediationTemplate Custom Resource (CR), which is used by the Node Health Check Operator (NHC). This CR defines the fence agent to be used in the cluster with all the required parameters for remediating the nodes. There may be many FenceAgentsRemediationTemplate CRs, at most one for each fence agent, and when NHC is being used it can choose the FenceAgentsRemediationTemplate as the remediationTemplate to be used for power-cycling the node.

The FenceAgentsRemediationTemplate CR resembles the following YAML file: 

apiVersion: fence-agents-remediation.medik8s.io/v1alpha1
kind: FenceAgentsRemediationTemplate
metadata:
  name: fence-agents-remediation-template-fence-ipmilan
  namespace: openshift-workload-availability
spec:
  template:
    spec:
      agent: fence_ipmilan 1
      nodeparameters: 2
        --ipport:
          master-0-0: '6230'
          master-0-1: '6231'
          master-0-2: '6232'
          worker-0-0: '6233'
          worker-0-1: '6234'
          worker-0-2: '6235'
      sharedparameters: 3
        '--action': reboot
        '--ip': 192.168.123.1
        '--lanplus': ''
        '--password': password
        '--username': admin
      retryCount: '5' 4
      retryInterval: '5' 5
      timeout: '60' 6
1
Displays the name of the fence agent to be executed, for example, fence_ipmilan.
2
Displays the node-specific parameters for executing the fence agent, for example, ipport.
3
Displays the cluster-wide parameters for executing the fence agent, for example, username.
4
Displays the number of times to retry the fence agent command in case of failure. The default number of attempts is 5.
5
Displays the interval between retries in seconds. The default is 5 seconds.
6
Displays the timeout for the fence agent command in seconds. The default is 60 seconds.

3.4.1. Understanding the Fence Agents Remediation Template configuration

The Fence Agents Remediation Operator also creates the FenceAgentsRemediationTemplate Custom Resource Definition (CRD). This CRD defines the remediation strategy for the nodes that is aimed to recover workloads faster. The following remediation strategies are available:

ResourceDeletion
This remediation strategy removes the pods on the node. This strategy recovers workloads faster.
OutOfServiceTaint
This remediation strategy implicitly causes the removal of the pods and associated volume attachments on the node. It achieves this by placing the OutOfServiceTaint taint on the node. The OutOfServiceTaint strategy also represents a non-graceful node shutdown. A non-graceful node shutdown occurs when a node is shut down and not detected, instead of triggering an in-operating system shutdown. This strategy has been supported on technology preview since OpenShift Container Platform version 4.13, and on general availability since OpenShift Container Platform version 4.15.

The FenceAgentsRemediationTemplate CR resembles the following YAML file: 

apiVersion: fence-agents-remediation.medik8s.io/v1alpha1
kind: FenceAgentsRemediationTemplate
metadata:
  name: fence-agents-remediation-<remediation_object>-deletion-template 1
  namespace: openshift-workload-availability
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 taint; for example, fence-agents-remediation-resource-deletion-template.
2
Specifies the remediation strategy. The remediation strategy can either be ResourceDeletion or OutOfServiceTaint.

3.5. Troubleshooting the Fence Agents Remediation Operator

3.5.1. General troubleshooting

Issue
You want to troubleshoot issues with the Fence Agents Remediation Operator.
Resolution

Check the Operator logs. 

$ oc logs <fence-agents-remediation-controller-manager-name> -c manager -n <namespace-name>

3.5.2. Unsuccessful remediation

Issue
An unhealthy node was not remediated.
Resolution

Verify that the FenceAgentsRemediation CR was created by running the following command: 

$ oc get far -A

If the NodeHealthCheck controller did not create the FenceAgentsRemediation CR when the node turned unhealthy, check the logs of the NodeHealthCheck controller. Additionally, ensure that the NodeHealthCheck CR includes the required specification to use the remediation template.

If the FenceAgentsRemediation CR was created, ensure that its name matches the unhealthy node object.

3.5.3. Fence Agents Remediation Operator resources exist after uninstalling the Operator

Issue
The Fence Agents Remediation Operator resources, such as the remediation CR and the remediation template CR, exist after uninstalling the Operator.
Resolution

To remove the Fence Agents Remediation Operator resources, you can delete the resources by selecting the "Delete all operand instances for this operator" checkbox before uninstalling. This checkbox feature is only available in Red Hat OpenShift since version 4.13. For all versions of Red Hat OpenShift, you can delete the resources by running the following relevant command for each resource type: 

$ oc delete far <fence-agents-remediation> -n <namespace>
$ oc delete fartemplate <fence-agents-remediation-template> -n <namespace>

The remediation CR far must be created and deleted by the same entity, for example, NHC. If the remediation CR far is still present, it is deleted, together with the FAR operator.

The remediation template CR fartemplate only exists if you use FAR with NHC. When the FAR operator is deleted using the web console, the remediation template CR fartemplate is also deleted.

3.6. Gathering data about the Fence Agents Remediation Operator

To collect debugging information about the Fence Agents Remediation Operator, use the must-gather tool. For information about the must-gather image for the Fence Agents Remediation Operator, see Gathering data about specific features.

3.7. Agents supported by the Fence Agents Remediation Operator

This section describes the agents currently supported by the Fence Agents Remediation Operator.

Most of the supported agents can be grouped by the node’s hardware proprietary and usage, as follows:

  1. BareMetal
  2. Virtualization
  3. Intel
  4. HP
  5. IBM
  6. VMware
  7. Cisco
  8. APC
  9. Dell
  10. Other
Table 3.1. BareMetal - Using the Redfish management interface is recommended, unless it is not supported.
AgentDescription

fence_redfish

An I/O Fencing agent that can be used with Out-of-Band controllers that support Redfish APIs.

fence_ipmilan [a]

An I/O Fencing agent that can be used with machines controlled by IPMI.

[a] This description also applies for the agents fence_ilo3, fence_ilo4, fence_ilo5, fence_imm, fence_idrac, and fence_ipmilanplus.
Table 3.2. Virtualization
AgentDescription

fence_rhevm

An I/O Fencing agent that can be used with RHEV-M REST API to fence virtual machines.

fence_virt [a]

An I/O Fencing agent that can be used with virtual machines.

[a] This description also applies for the agent fence_xvm.
Table 3.3. Intel
AgentDescription

fence_amt_ws

An I/O Fencing agent that can be used with Intel AMT (WS).

fence_intelmodular

An I/O Fencing agent that can be used with Intel Modular device (tested on Intel MFSYS25, should also work with MFSYS35).

Table 3.4. HP - agents for the iLO management interface or BladeSystem.
AgentDescription

fence_ilo [a]

An I/O Fencing agent that can be used for HP servers with the Integrated Light Out (iLO) PCI card.

fence_ilo_ssh [b]

A fencing agent that can be used to connect to an iLO device. It logs into device via ssh and reboot a specified outlet.

fence_ilo_moonshot

An I/O Fencing agent that can be used with HP Moonshot iLO.

fence_ilo_mp

An I/O Fencing agent that can be used with HP iLO MP.

fence_hpblade

An I/O Fencing agent that can be used with HP BladeSystem and HP Integrity Superdome X.

[a] This description also applies for the agent fence_ilo2.
[b] This description also applies for the agents fence_ilo3_ssh, fence_ilo4_ssh, and fence_ilo5_ssh.
Table 3.5. IBM
AgentDescription

fence_bladecenter

An I/O Fencing agent that can be used with IBM Bladecenters with recent enough firmware that includes telnet support.

fence_ibmblade

An I/O Fencing agent that can be used with IBM BladeCenter chassis.

fence_ipdu

An I/O Fencing agent that can be used with the IBM iPDU network power switch.

fence_rsa

An I/O Fencing agent that can be used with the IBM RSA II management interface.

Table 3.6. VMware
AgentDescription

fence_vmware_rest

An I/O Fencing agent that can be used with VMware API to fence virtual machines.

fence_vmware_soap

An I/O Fencing agent that can be used with the virtual machines managed by VMWare products that have SOAP API v4.1+.

Table 3.7. Cisco
AgentDescription

fence_cisco_mds

An I/O Fencing agent that can be used with any Cisco MDS 9000 series with SNMP enabled device.

fence_cisco_ucs

An I/O Fencing agent that can be used with Cisco UCS to fence machines.

Table 3.8. APC
AgentDescription

fence_apc

An I/O Fencing agent that can be used with the APC network power switch.

fence_apc_snmp

An I/O Fencing agent that can be used with the APC network power switch or Tripplite PDU devices.

Table 3.9. Dell
AgentDescription

fence_drac5

An I/O Fencing agent that can be used with the Dell Remote Access Card v5 or CMC (DRAC).

Table 3.10. Other - agents for usage not listed in the previous tables.
AgentDescription

fence_brocade

An I/O Fencing agent that can be used with Brocade FC switches.

fence_compute

A resource that can be used to tell Nova that compute nodes are down and to reschedule flagged instances.

fence_eaton_snmp

An I/O Fencing agent that can be used with the Eaton network power switch.

fence_emerson

An I/O Fencing agent that can be used with MPX and MPH2 managed rack PDU.

fence_eps

An I/O Fencing agent that can be used with the ePowerSwitch 8M+ power switch to fence connected machines.

fence_evacuate

A resource that can be used to reschedule flagged instances.

fence_heuristics_ping

A resource that can be used with ping-heuristics to control execution of another fence agent on the same fencing level.

fence_ifmib

An I/O Fencing agent that can be used with any SNMP IF-MIB capable device.

fence_kdump

An I/O Fencing agent that can be used with the kdump crash recovery service.

fence_mpath

An I/O Fencing agent that can be used with SCSI-3 persistent reservations to control access multipath devices.

fence_rsb

An I/O Fencing agent that can be used with the Fujitsu-Siemens RSB management interface.

fence_sbd

An I/O Fencing agent that can be used in environments where sbd can be used (shared storage).

fence_scsi

An I/O Fencing agent that can be used with SCSI-3 persistent reservations to control access to shared storage devices.

fence_wti

An I/O Fencing agent that can be used with the WTI Network Power Switch (NPS).

3.8. Additional resources

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