dns-resolution-check

DNS Status Check

The DNS Status Check checks for failures with DNS, including resolving within the cluster and outside of the cluster. Each check lookups and verifies one hostname. Default KHCheck configurations applied are:

• internalDNSStatusCheck.yaml
  • Hostname: kubernetes.default
  • Check Name: dns-status-internal
• externalDNSStatusCheck.yaml
  • Hostname: google.com
  • Check Name: dns-status-external

The check runs every 2 minutes (spec.runInterval), with a check timeout set to 15 minutes (spec.timeout). If the check does not complete within the given timeout it will report a timeout error on the status page.

To verify other hostnames, apply another KHCheck configuration file with a different HOSTNAME environment variable.

DNS Status Check Kube Spec:

apiVersion: comcast.github.io/v1
kind: KuberhealthyCheck
metadata:
  name: dns-status-internal
  namespace: kuberhealthy
spec:
  runInterval: 2m
  timeout: 15m
  podSpec:
    containers:
      - env:
          - name: HOSTNAME
            value: "kubernetes.default"
          - name: NODE_NAME
            valueFrom:
              fieldRef:
                fieldPath: spec.nodeName
        image: kuberhealthy/dns-resolution-check:v1.5.0
        imagePullPolicy: IfNotPresent
        name: main
        resources:
          requests:
            cpu: 10m
            memory: 50Mi

Checking endpoints behind DNS Service

In order to check endpoints behind the DNS service, add a DNS_NODE_SELECTOR and NAMESPACE variable to the spec file denoting where your DNS pods are.

DNS_NODE_SELECTOR is a label selector which will be used to select the DNS endpoints to query against.

apiVersion: comcast.github.io/v1
kind: KuberhealthyCheck
metadata:
  name: dns-status-internal
  namespace: kuberhealthy
spec:
  runInterval: 2m
  timeout: 15m
  podSpec:
    containers:
      - env:
          - name: HOSTNAME
            value: "kubernetes.default"
          - name: NAMESPACE
            value: "kube-system"
          - name: DNS_NODE_SELECTOR
            value: apps=k8s-dns
          - name: NODE_NAME
            valueFrom:
              fieldRef:
                fieldPath: spec.nodeName
        image: kuberhealthy/dns-resolution-check:v1.5.0
        imagePullPolicy: IfNotPresent
        name: main
        resources:
          requests:
            cpu: 10m
            memory: 50Mi

How-to

To implement the DNS Status Check with Kuberhealthy, run

kubectl apply -f https://raw.githubusercontent.com/kuberhealthy/kuberhealthy/2.0.0/cmd/dns-resolution-check/externalDNSStatusCheck.yaml kubectl apply -f https://raw.githubusercontent.com/kuberhealthy/kuberhealthy/2.0.0/cmd/dns-resolution-check/internalDNSStatusCheck.yaml