Alert "elasticsearch-metrics targets in Namespace openshift-logging namespace have been unreachable" is firing in OpenShift Container Platform

Issue

• The following alert is firing in the OpenShift Container Platform cluster:

  x% of the elasticsearch-metrics/elasticsearch-metrics targets in Namespace openshift-logging namespace have been unreachable
  

• The Cluster Logging Operator is showing the following messages in the status field:

  $ oc get ClusterLogging instance -o yaml
  [..]
      nodeConditions:
      elasticsearch-cdm-2wn4b6sn-1:
      - lastTransitionTime: "2023-05-08T07:06:32Z"
        message: Disk storage usage for node is 1.18Tb (87.59966182226196%). Shards will be not be allocated on this node.
        reason: Disk Watermark Low
        status: "True"
        type: NodeStorage
      elasticsearch-cdm-2wn4b6sn-2:
      - lastTransitionTime: "2023-05-08T07:06:32Z"
        message: Disk storage usage for node is 1.17Tb (87.17254571557135%). Shards will be not be allocated on this node.
        reason: Disk Watermark Low
        status: "True"
        type: NodeStorage
      elasticsearch-cdm-2wn4b6sn-3:
      - lastTransitionTime: "2023-05-08T07:06:32Z"
        message: Disk storage usage for node is 1.16Tb (86.54566843101432%). Shards will be not be allocated on this node.
        reason: Disk Watermark Low
        status: "True"
        type: NodeStorage
  
  [..]