Monitor Node Health

Node Problem Detector is a daemon for monitoring and reporting about a node's health. You can run Node Problem Detector as a DaemonSet or as a standalone daemon. Node Problem Detector collects information about node problems from various daemons and reports these conditions to the API server as NodeCondition and Event.

To learn how to install and use Node Problem Detector, see Node Problem Detector project documentation.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

• Katacoda
• Play with Kubernetes

Limitations

• Node Problem Detector only supports file based kernel log. Log tools such as journald are not supported.

• Node Problem Detector uses the kernel log format for reporting kernel issues. To learn how to extend the kernel log format, see Add support for another log format.

Enabling Node Problem Detector

Some cloud providers enable Node Problem Detector as an Addon. You can also enable Node Problem Detector with kubectl or by creating an Addon pod.

Using kubectl to enable Node Problem Detector

kubectl provides the most flexible management of Node Problem Detector. You can overwrite the default configuration to fit it into your environment or to detect customized node problems. For example:

1. Create a Node Problem Detector configuration similar to node-problem-detector.yaml:

   debug/node-problem-detector.yaml

   apiVersion: apps/v1
   kind: DaemonSet
   metadata:
     name: node-problem-detector-v0.1
     namespace: kube-system
     labels:
       k8s-app: node-problem-detector
       version: v0.1
       kubernetes.io/cluster-service: "true"
   spec:
     selector:
       matchLabels:
         k8s-app: node-problem-detector  
         version: v0.1
         kubernetes.io/cluster-service: "true"
     template:
       metadata:
         labels:
           k8s-app: node-problem-detector
           version: v0.1
           kubernetes.io/cluster-service: "true"
       spec:
         hostNetwork: true
         containers:
         - name: node-problem-detector
           image: k8s.gcr.io/node-problem-detector:v0.1
           securityContext:
             privileged: true
           resources:
             limits:
               cpu: "200m"
               memory: "100Mi"
             requests:
               cpu: "20m"
               memory: "20Mi"
           volumeMounts:
           - name: log
             mountPath: /log
             readOnly: true
         volumes:
         - name: log
           hostPath:
             path: /var/log/

   Note: You should verify that the system log directory is right for your operating system distribution.

2. Start node problem detector with kubectl:

   kubectl apply -f https://k8s.io/examples/debug/node-problem-detector.yaml
   

Using an Addon pod to enable Node Problem Detector

If you are using a custom cluster bootstrap solution and don't need to overwrite the default configuration, you can leverage the Addon pod to further automate the deployment.

Create node-problem-detector.yaml, and save the configuration in the Addon pod's directory /etc/kubernetes/addons/node-problem-detector on a control plane node.

Overwrite the configuration

The default configuration is embedded when building the Docker image of Node Problem Detector.

However, you can use a ConfigMap to overwrite the configuration:

1. Change the configuration files in config/

2. Create the ConfigMap node-problem-detector-config:

   kubectl create configmap node-problem-detector-config --from-file=config/
   

3. Change the node-problem-detector.yaml to use the ConfigMap:

   debug/node-problem-detector-configmap.yaml

   apiVersion: apps/v1
   kind: DaemonSet
   metadata:
     name: node-problem-detector-v0.1
     namespace: kube-system
     labels:
       k8s-app: node-problem-detector
       version: v0.1
       kubernetes.io/cluster-service: "true"
   spec:
     selector:
       matchLabels:
         k8s-app: node-problem-detector  
         version: v0.1
         kubernetes.io/cluster-service: "true"
     template:
       metadata:
         labels:
           k8s-app: node-problem-detector
           version: v0.1
           kubernetes.io/cluster-service: "true"
       spec:
         hostNetwork: true
         containers:
         - name: node-problem-detector
           image: k8s.gcr.io/node-problem-detector:v0.1
           securityContext:
             privileged: true
           resources:
             limits:
               cpu: "200m"
               memory: "100Mi"
             requests:
               cpu: "20m"
               memory: "20Mi"
           volumeMounts:
           - name: log
             mountPath: /log
             readOnly: true
           - name: config # Overwrite the config/ directory with ConfigMap volume
             mountPath: /config
             readOnly: true
         volumes:
         - name: log
           hostPath:
             path: /var/log/
         - name: config # Define ConfigMap volume
           configMap:
             name: node-problem-detector-config

4. Recreate the Node Problem Detector with the new configuration file:

   # If you have a node-problem-detector running, delete before recreating
   kubectl delete -f https://k8s.io/examples/debug/node-problem-detector.yaml
   kubectl apply -f https://k8s.io/examples/debug/node-problem-detector-configmap.yaml
   

Overwriting a configuration is not supported if a Node Problem Detector runs as a cluster Addon. The Addon manager does not support ConfigMap.

Kernel Monitor

Kernel Monitor is a system log monitor daemon supported in the Node Problem Detector. Kernel monitor watches the kernel log and detects known kernel issues following predefined rules.

The Kernel Monitor matches kernel issues according to a set of predefined rule list in config/kernel-monitor.json. The rule list is extensible. You can expand the rule list by overwriting the configuration.

Add new NodeConditions

To support a new NodeCondition, create a condition definition within the conditions field in config/kernel-monitor.json, for example:

{
  "type": "NodeConditionType",
  "reason": "CamelCaseDefaultNodeConditionReason",
  "message": "arbitrary default node condition message"
}

Detect new problems

To detect new problems, you can extend the rules field in config/kernel-monitor.json with a new rule definition:

{
  "type": "temporary/permanent",
  "condition": "NodeConditionOfPermanentIssue",
  "reason": "CamelCaseShortReason",
  "message": "regexp matching the issue in the kernel log"
}

Configure path for the kernel log device

Check your kernel log path location in your operating system (OS) distribution. The Linux kernel log device is usually presented as /dev/kmsg. However, the log path location varies by OS distribution. The log field in config/kernel-monitor.json represents the log path inside the container. You can configure the log field to match the device path as seen by the Node Problem Detector.

Add support for another log format

Kernel monitor uses the Translator plugin to translate the internal data structure of the kernel log. You can implement a new translator for a new log format.

Recommendations and restrictions

It is recommended to run the Node Problem Detector in your cluster to monitor node health. When running the Node Problem Detector, you can expect extra resource overhead on each node. Usually this is fine, because:

• The kernel log grows relatively slowly.
• A resource limit is set for the Node Problem Detector.
• Even under high load, the resource usage is acceptable. For more information, see the Node Problem Detector benchmark result.