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Kubenurse

Kubenurse

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.

Here's an overview of the checks performed by kubenurse, which are exposed as labels for the various duration/error prometheus metrics.

kubenurse request types

Grafana dashboard

Once the kubenurse pods are up and running and scraped by your metrics agent, you can import the example dashboard to start scrutinizing network latencies and errors.

Grafana overview

Metrics

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

node-to-node network latencies and errors
pod-to-apiserver communication
Ingress roundtrip latencies and errors
Service roundtrip latencies and errors (kube-proxy / your CNI)
Major kube-apiserver issues
kube-dns (or CoreDNS) errors
External DNS resolution errors (ingress URL resolution)

At /metrics you will find the following metrics:

metric name	labels	description
~~`kubenurse request duration`~~	`type`	(deprecated since v1.13.0) latency histogram for request duration, replaced with the metric below.
`kubenurse httpclient request duration seconds`	`type`	latency histogram for request duration, partitioned by request type
`kubenurse httpclient trace request duration seconds`	`type, event`	latency histogram for httpclient trace metric instrumentation, partitioned by request type and httptrace connection events
`kubenurse httpclient requests total`	`type, code, method`	counter for the total number of http requests, partitioned by HTTP code, method, and request type
`kubenurse errors total`	`type, event`	error counter, partitioned by httptrace event and request type
`kubenurse neighbourhood incoming checks`	n\a	gauge which reports how many unique neighbours have queried the current pod in the last minute

For metrics partitioned with a type label, it is possible to precisely know which request type increased an error counter, or to compare the latencies of multiple request types, for example compare how your service and ingress latencies differ.

Some event labels include dns_start, got_conn, tls_handshake_done, and more. the details can be seen in the httptrace.go file.

Deployment

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.

Helm deployment

You can also deploy kubenurse with Helm, the Chart can be found in repository https://postfinance.github.io/kubenurse/ or directory ./helm/kubenurse/. The following command can be used to install kubenurse with Helm: helm upgrade [RELEASE_NAME] --install --repo https://postfinance.github.io/kubenurse/ kubenurse.

Helm parameters

<details> <summary>helm parameters list</summary>

Setting	Description	Default
daemonset.image.repository	The repository name	`postfinance/kubenurse`
daemonset.image.tag	The tag/ version of the image	`v1.4.0`
daemonset.podLabels	Additional labels to be added to the pods of the daemonset	`[]`
daemonset.podAnnotations	Additional annotations to be added to the pods of the daemonset	`[]`
daemonset.podSecurityContext	The security context of the daemonset	`{}`
daemonset.priorityClassName	The priority class name for the daemonset pods	`""`
daemonset.containerSecurityContext	The security context of the containers within the pods of the daemonset	`{}`
daemonset.containerResources	The container resources of the containers within the pods of the daemonset	`{}`
daemonset.containerImagePullPolicy	The container image pull policy the pods of the daemonset	`IfNotPresent`
daemonset.tolerations	The tolerations of the daemonset	See Default tolerations below
daemonset.dnsConfig	Specifies the DNS parameters of the pods in the daemonset	`{}`
daemonset.volumeMounts	Additional volumeMounts to be added to the pods of the daemonset	`[]`
daemonset.volumes	Additional volumes to be added to the daemonset	`[]`
serviceMonitor.enabled	Adds a ServiceMonitor for use with Prometheus-operator	`false`
serviceMonitor.labels	Additional labels to be added to the ServiceMonitor	`{}`
serviceAccount.name	The name of the service account which is used	`Release.Name`
service.name	The name of service which exposes the kubenurse application	`8080-8080`
service.port	The port number of the service	`8080`
service.labels	Additional labels to be added to the Service
ingress.enabled	Enable/ Disable the ingress	`true`
ingress.className	The classname of the ingress controller (e.g. the nginx ingress controller)	`nginx`
ingress.url	The url of the ingress; e.g. kubenurse.westeurope.cloudapp.example.com	`dummy-kubenurse.example.com`
insecure	Set `KUBENURSE_INSECURE` environment variable	`true`
allow_unschedulable	Sets `KUBENURSE_ALLOW_UNSCHEDULABLE` environment variable	`false`
neighbour_filter	Sets `KUBENURSE_NEIGHBOUR_FILTER` environment variable	`app.kubernetes.io/name=kubenurse`
neighbour_limit	Sets `KUBENURSE_NEIGHBOUR_LIMIT` environment variable	`10`
histogram_buckets	Sets `KUBENURSE_HISTOGRAM_BUCKETS` environment variable
extra_ca	Sets `KUBENURSE_EXTRA_CA` environment variable
extra_checks	Sets `KUBENURSE_EXTRA_CHECKS` environment variable
check_api_server_direct	Sets `KUBENURSE_CHECK_API_SERVER_DIRECT` environment variable	`true`
check_api_server_dns	Sets `KUBENURSE_CHECK_API_SERVER_DNS` environment variable	`true`
check_me_ingress	Sets `KUBENURSE_CHECK_ME_INGRESS` environment variable	`true`
check_me_service	Sets `KUBENURSE_CHECK_ME_SERVICE` environment variable	`true`
check_neighbourhood	Sets `KUBENURSE_CHECK_NEIGHBOURHOOD` environment variable	`true`
check_interval	Sets `KUBENURSE_CHECK_INTERVAL` environment variable	`5s`
reuse_connections	Sets `KUBENURSE_REUSE_CONNECTIONS` environment variable	`false`
use_tls	Sets `KUBENURSE_USE_TLS` environment variable	`false`
cert_file	Sets `KUBENURSE_CERT_FILE` environment variable
cert_key	Sets `KUBENURSE_CERT_KEY` environment variable

</details>

Configuration

<details> <summary>kubenurse environment variables list</summary>

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_EXTRA_CHECKS: Additional checks, specified as a list (separated by a vertical bar |) where each entry of the list has the format: <metric_name>:<url_to_check>. For example google:https://www.google.ch/|cloudflare:https://www.cloudflare.com/
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_NEIGHBOUR_LIMIT: The maximum number of neighbours each kubenurse will query
KUBENURSE_ALLOW_UNSCHEDULABLE: If this is "true", path checks to neighbouring kubenurses are made even if they are running on unschedulable nodes.
KUBENURSE_CHECK_API_SERVER_DIRECT: If this is "true" kubenurse will perform the check [API Server Direct](#API Server Direct). default is "true"
KUBENURSE_CHECK_API_SERVER_DNS: If this is "true", kubenurse will perform the check [API Server DNS](#API Server DNS). default is "true"
KUBENURSE_CHECK_ME_INGRESS: If this is "true", kubenurse will perform the check [Me Ingress](#Me Ingress). default is "true"
KUBENURSE_CHECK_ME_SERVICE: If this is "true", kubenurse will perform the check [Me Service](#Me Service). default is "true"
KUBENURSE_CHECK_NEIGHBOURHOOD: If this is "true", kubenurse will perform the check Neighbourhood. default is "true"
KUBENURSE_CHECK_INTERVAL: the frequency to perform kubenurse checks. the string should be formatted for time.ParseDuration. defaults to 5s
KUBENURSE_REUSE_CONNECTIONS: whether to reuse connections or not for all checks. default is "false"
KUBENURSE_HISTOGRAM_BUCKETS: optional comma-separated list of float64, used in place of the default prometheus histogram buckets
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

</details>

HTTP Endpoints

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"
   ],
   ...
  }
}

Health Checks

Every five seconds, the checks described below are run.

API Server Direct

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

Metric type: api_server_direct

API Server DNS

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

Me Ingress

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

Me Service

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

Neighbourhood

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

Neighbourhood filtering

The number of checks for the neighbourhood used to grow as $O(N^2)$, which rendered kubenurse impractical on large clusters, as documented in issue #55. To combat this, a node filtering feature was implemented, which works as follows

kubenurse computes the sha256 checksums for all neighbours' node names
it sorts those checksums (this is actually implemented with a max-heap)
it computes its own node name checksum, and queries the next 10 (per default) nodes in the sorted checksums list

Here's an example with 6 nodes, where each node queries the next 3 nodes:

node filtering drawing

Thanks to this, every node is making queries to the same 10 nodes, unless one of those nodes disappears, in which case kubenurse will pick the next node in the sorted checksums list. This comes with several advantages:

because of the way we first hash the node names, the checks are randomly distributed, independant of the node names. if we only picked the 10 next nodes in a sorted list of the node names, then we might have biased the results in environments where node names are sequential
metrics-wise, a kubenurse pod should typically only have entries for ca. 10 other neighbouring nodes worth of checks, which greatly reduces the load on your monitoring infrastructure
because we use a deterministic algorithm to choose which nodes to query, the metrics churn rate stays minimal. (that is, if we randomly picked 10 nodes for every check, then in the end there would be one prometheus bucket for every node on the cluster, which would put useless load on the monitoring infrastructure)

Per default, the neighbourhood filtering is set to 10 nodes, which means that on cluster with more than 10 nodes, each kubenurse will query exactly 10 nodes, as described above.

Neighbourhood incoming checks metric

It is possible to check that each node receives the proper number of neighbourhood queries with the kubenurse_neighbourhood_incoming_checks metric. If you have the neighbourhood limit set to e.g. 10, then this metric should be equal to 10 on all nodes, with some variations during a rollout restart.

To bypass the node filtering feature, you simply need to set the KUBENURSE_NEIGHBOUR_LIMIT environment variable to 0.