Improving DNS Reliability with NodeLocalDNS in Kubernetes

# Copyright 2018 The Kubernetes Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

apiVersion: v1
kind: ServiceAccount
metadata:
  name: node-local-dns
  namespace: kube-system
  labels:
    kubernetes.io/cluster-service: "true"
    addonmanager.kubernetes.io/mode: Reconcile
---
apiVersion: v1
kind: Service
metadata:
  name: kube-dns-upstream
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/cluster-service: "true"
    addonmanager.kubernetes.io/mode: Reconcile
    kubernetes.io/name: "KubeDNSUpstream"
spec:
  ports:
  - name: dns
    port: 53
    protocol: UDP
    targetPort: 53
  - name: dns-tcp
    port: 53
    protocol: TCP
    targetPort: 53
  selector:
    k8s-app: kube-dns
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: node-local-dns
  namespace: kube-system
  labels:
    addonmanager.kubernetes.io/mode: Reconcile
data:
  Corefile: |
    __PILLAR__DNS__DOMAIN__:53 {
        errors
        cache {
                success 9984 30
                denial 9984 5
        }
        reload
        loop
        bind __PILLAR__LOCAL__DNS__ __PILLAR__DNS__SERVER__
        forward . __PILLAR__CLUSTER__DNS__ {
                force_tcp
        }
        prometheus :9253
        health __PILLAR__LOCAL__DNS__:8080
        }
    in-addr.arpa:53 {
        errors
        cache 30
        reload
        loop
        bind __PILLAR__LOCAL__DNS__ __PILLAR__DNS__SERVER__
        forward . __PILLAR__CLUSTER__DNS__ {
                force_tcp
        }
        prometheus :9253
        }
    ip6.arpa:53 {
        errors
        cache 30
        reload
        loop
        bind __PILLAR__LOCAL__DNS__ __PILLAR__DNS__SERVER__
        forward . __PILLAR__CLUSTER__DNS__ {
                force_tcp
        }
        prometheus :9253
        }
    .:53 {
        errors
        cache 30
        reload
        loop
        bind __PILLAR__LOCAL__DNS__ __PILLAR__DNS__SERVER__
        forward . __PILLAR__UPSTREAM__SERVERS__
        prometheus :9253
        }
---
apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: node-local-dns
  namespace: kube-system
  labels:
    k8s-app: node-local-dns
    kubernetes.io/cluster-service: "true"
    addonmanager.kubernetes.io/mode: Reconcile
spec:
  updateStrategy:
    rollingUpdate:
      maxUnavailable: 10%
  selector:
    matchLabels:
      k8s-app: node-local-dns
  template:
    metadata:
      labels:
        k8s-app: node-local-dns
      annotations:
        prometheus.io/port: "9253"
        prometheus.io/scrape: "true"
    spec:
      priorityClassName: system-node-critical
      serviceAccountName: node-local-dns
      hostNetwork: true
      dnsPolicy: Default  # Don't use cluster DNS.
      tolerations:
      - key: "CriticalAddonsOnly"
        operator: "Exists"
      - effect: "NoExecute"
        operator: "Exists"
      - effect: "NoSchedule"
        operator: "Exists"
      containers:
      - name: node-cache
        image: registry.k8s.io/dns/k8s-dns-node-cache:1.25.0
        resources:
          requests:
            cpu: 25m
            memory: 5Mi
        args: [ "-localip", "__PILLAR__LOCAL__DNS__,__PILLAR__DNS__SERVER__", "-conf", "/etc/Corefile", "-upstreamsvc", "kube-dns-upstream" ]
        securityContext:
          capabilities:
            add:
            - NET_ADMIN
        ports:
        - containerPort: 53
          name: dns
          protocol: UDP
        - containerPort: 53
          name: dns-tcp
          protocol: TCP
        - containerPort: 9253
          name: metrics
          protocol: TCP
        livenessProbe:
          httpGet:
            host: __PILLAR__LOCAL__DNS__
            path: /health
            port: 8080
          initialDelaySeconds: 60
          timeoutSeconds: 5
        volumeMounts:
        - mountPath: /run/xtables.lock
          name: xtables-lock
          readOnly: false
        - name: config-volume
          mountPath: /etc/coredns
        - name: kube-dns-config
          mountPath: /etc/kube-dns
      volumes:
      - name: xtables-lock
        hostPath:
          path: /run/xtables.lock
          type: FileOrCreate
      - name: kube-dns-config
        configMap:
          name: kube-dns
          optional: true
      - name: config-volume
        configMap:
          name: node-local-dns
          items:
            - key: Corefile
              path: Corefile.base
---
# A headless service is a service with a service IP but instead of load-balancing it will return the IPs of our associated Pods.
# We use this to expose metrics to Prometheus.
apiVersion: v1
kind: Service
metadata:
  annotations:
    prometheus.io/port: "9253"
    prometheus.io/scrape: "true"
  labels:
    k8s-app: node-local-dns
  name: node-local-dns
  namespace: kube-system
spec:
  clusterIP: None
  ports:
    - name: metrics
      port: 9253
      targetPort: 9253
  selector:
    k8s-app: node-local-dns