kubenurse is a little service that monitors all network connections in a Kubernetes cluster. Kubenurse measures request durations, records errors and exports those metrics in Prometheus format.

You can get the Docker image from Docker Hub. The examples directory contains manifests which can be used to deploy kubenurse to the kube-system namespace of your cluster.

You can also deploy kubenurse with Helm, the Chart can be found in the helm/kubenurse directory.
The following command can be used to install kubenurse with Helm: helm upgrade [RELEASE_NAME] --install -f values.yaml ./helm/kubenurse/

After everything is set up and Prometheus scrapes the kubenurses, you can build dashboards that show network latencies and errors or use the metrics for alarming.

kubenurse is configured with environment variables:

• KUBENURSE_INGRESS_URL: An URL to the kubenurse in order to check the ingress
• KUBENURSE_SERVICE_URL: An URL to the kubenurse in order to check the Kubernetes service
• KUBENURSE_INSECURE: If "true", TLS connections will not validate the certificate
• KUBENURSE_EXTRA_CA: Additional CA cert path for TLS connections
• KUBENURSE_NAMESPACE: Namespace in which to look for the neighbour kubenurses
• KUBENURSE_NEIGHBOUR_FILTER: A Kubernetes label selector (eg. app=kubenurse) to filter neighbour kubenurses
• KUBENURSE_ALLOW_UNSCHEDULABLE: If this is "true", path checks to neighbouring kubenurses are made even if they are running on unschedulable nodes.
• KUBENURSE_USE_TLS: If this is "true", enable TLS endpoint on port 8443
• KUBENURSE_CERT_FILE: Certificate to use with TLS endpoint
• KUBENURSE_CERT_KEY: Key to use with TLS endpoint

Following variables are injected to the Pod by Kubernetes and should not be defined manually:

• KUBERNETES_SERVICE_HOST: Host to communicate to the kube-apiserver
• KUBERNETES_SERVICE_PORT: Port to communicate to the kube-apiserver

The used http client appends the certificate /var/run/secrets/kubernetes.io/serviceaccount/ca.crt if found.

The kubenurse service listens for http requests on port 8080 (optionally https on port 8443) and exposes endpoints:

• /: Redirects to /alive
• /alive: Returns a pretty printed JSON with the check results, described below
• /alwayshappy: Returns http-200 which is used for testing itself
• /metrics: Exposes Prometheus metrics

The /alive endpoint returns a JSON like this with status code 200 if everything is OK else 500:

{
  "api_server_direct": "ok",
  "api_server_dns": "ok",
  "me_ingress": "ok",
  "me_service": "ok",
  "hostname": "kubenurse-1234-x2bwx",
  "neighbourhood_state": "ok",
  "neighbourhood": [
   {
    "PodName": "kubenurse-1234-8fh2x",
    "PodIP": "10.10.10.67",
    "HostIP": "10.12.12.66",
    "NodeName": "k8s-66.example.com",
    "Phase": "Running"
   },
   {
    "PodName": "kubenurse-1234-ffjbs",
    "PodIP": "10.10.10.138",
    "HostIP": "10.12.12.89",
    "NodeName": "k8s-89.example.com",
    "Phase": "Running"
   }
  ],
  "headers": {
   "Accept": [
    "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8"
   ],
   "Accept-Encoding": [
    "gzip, deflate, br"
   ],
   ...
  }
}

Every five seconds and on every access of /alive, the checks described below are run. Check results are cached for 3 seconds in order to prevent excessive network traffic.

A little illustration of what communication occurs, is here:

Checks the /version endpoint of the Kubernetes API Server through the direct link (KUBERNETES_SERVICE_HOST, KUBERNETES_SERVICE_PORT).

Metric type: api_server_direct

Checks the /version endpoint of the Kubernetes API Server through the Cluster DNS URL https://kubernetes.default.svc:$KUBERNETES_SERVICE_PORT. This also verifies a working kube-dns deployment.

Metric type: api_server_dns

Checks if the kubenurse is reachable at the /alwayshappy endpoint behind the ingress. This address is provided by the environment variable KUBENURSE_INGRESS_URL that could look like https://kubenurse.example.com. This also verifies a correct upstream DNS resolution.

Metric type: me_ingress

Checks if the kubenurse is reachable at the /alwayshappy endpoint through the Kubernetes service. The address is provided by the environment variable KUBENURSE_SERVICE_URL that could look like http://kubenurse.mynamespace.default.svc:8080. This also verifies a working kube-proxy setup.

Metric type: me_service

Checks if every neighbour kubenurse is reachable at the /alwayshappy endpoint. Neighbours are discovered by querying the kube-apiserver for every Pod in the KUBENURSE_NAMESPACE with label KUBENURSE_NEIGHBOUR_FILTER. The request is done directly to the Pod-IP (port 8080, or 8443 if TLS is enabled) and the metric types contains the prefix path_ and the hostname of the kubelet on which the neighbour kubenurse should run. Only kubenurses on nodes that are schedulable are considered as neighbours, this can be changed by setting KUBENURSE_ALLOW_UNSCHEDULABLE="true".

Metric type: path_$KUBELET_HOSTNAME

All performed checks expose metrics which can be used to monitor/alert:

• SDN network latencies and errors
• kubelet-to-kubelet network latencies and errors
• pod-to-apiserver communication
• Ingress roundtrip latencies and errors
• Service roundtrip latencies and errors (kube-proxy)
• Major kube-apiserver issues
• kube-dns (or CoreDNS) errors
• External DNS resolution errors (ingress URL resolution)

At /metrics you will find these:

• kubenurse_errors_total: Kubenurse error counter partitioned by error type
• kubenurse_request_duration: Kubenurse request duration partitioned by error type, summary over one minute