Add CoreDNS support with various fixes

Added CoreDNS to downloads

Updated with labels. Should now work without RBAC too

Fix DNS settings on hosts

Rename CoreDNS service from kube-dns to coredns

Add rotate based on http://edgeofsanity.net/rant/2017/12/20/systemd-resolved-is-broken.html

Updated docs with CoreDNS info

Added labels and fixed minor settings from official yaml file: https://github.com/kubernetes/kubernetes/blob/release-1.9/cluster/addons/dns/coredns.yaml.sed

Added a secondary deployment and secondary service ip. This is to mitigate dns timeouts and create high resitency for failures. See discussion at 'https://github.com/coreos/coreos-kubernetes/issues/641#issuecomment-281174806'

Set dns list correct. Thanks to @whereismyjetpack

Only download KubeDNS or CoreDNS if selected

Move dns cleanup to its own file and import tasks based on dns mode

Fix install of KubeDNS when dnsmask_kubedns mode is selected

Add new dns option coredns_dual for dual stack deployment. Added variable to configure replicas deployed. Updated docs for dual stack deployment. Removed rotate option in resolv.conf.

Run DNS manifests for CoreDNS and KubeDNS

Set skydns servers on dual stack deployment

Use only one template for CoreDNS dual deployment

Set correct cluster ip for the dns server

docs/dns-stack.md

@@ -62,6 +62,14 @@ other queries are forwardet to the nameservers found in ``upstream_dns_servers``
 This does not install the dnsmasq DaemonSet and instructs kubelet to directly use kubedns/skydns for
 all queries.
 
+#### coredns
+This does not install the dnsmasq DaemonSet and instructs kubelet to directly use CoreDNS for
+all queries.
+
+#### coredns_dual
+This does not install the dnsmasq DaemonSet and instructs kubelet to directly use CoreDNS for
+all queries. It will also deploy a secondary CoreDNS stack
+
 #### manual
 This does not install dnsmasq or kubedns, but allows you to specify
 `manual_dns_server`, which will be configured on nodes for handling Pod DNS.

docs/vars.md

@@ -63,7 +63,8 @@ following default cluster paramters:
   bits in kube_pods_subnet dictates how many kube-nodes can be in cluster.
 * *dns_setup* - Enables dnsmasq
 * *dnsmasq_dns_server* - Cluster IP for dnsmasq (default is 10.233.0.2)
-* *skydns_server* - Cluster IP for KubeDNS (default is 10.233.0.3)
+* *skydns_server* - Cluster IP for DNS (default is 10.233.0.3)
+* *skydns_server_secondary* - Secondary Cluster IP for CoreDNS used with coredns_dual deployment (default is 10.233.0.4)
 * *cloud_provider* - Enable extra Kubelet option if operating inside GCE or
   OpenStack (default is unset)
 * *kube_hostpath_dynamic_provisioner* - Required for use of PetSets type in
@@ -105,9 +106,9 @@ Stack](https://github.com/kubernetes-incubator/kubespray/blob/master/docs/dns-st
 * *http_proxy/https_proxy/no_proxy* - Proxy variables for deploying behind a
   proxy. Note that no_proxy defaults to all internal cluster IPs and hostnames
   that correspond to each node.
-* *kubelet_deployment_type* - Controls which platform to deploy kubelet on. 
+* *kubelet_deployment_type* - Controls which platform to deploy kubelet on.
   Available options are ``host``, ``rkt``, and ``docker``. ``docker`` mode
-  is unlikely to work on newer releases. Starting with Kubernetes v1.7 
+  is unlikely to work on newer releases. Starting with Kubernetes v1.7
   series, this now defaults to ``host``. Before v1.7, the default was Docker.
   This is because of cgroup [issues](https://github.com/kubernetes/kubernetes/issues/43704).
 * *kubelet_load_modules* - For some things, kubelet needs to load kernel modules.  For example,

inventory/sample/group_vars/k8s-cluster.yml

@@ -111,14 +111,17 @@ kube_apiserver_insecure_port: 8080 # (http)
 
 # Kube-proxy proxyMode configuration.
 # Can be ipvs, iptables
-kube_proxy_mode: iptables 
+kube_proxy_mode: iptables
+
+## Encrypting Secret Data at Rest (experimental)
+kube_encrypt_secret_data: false
 
 # DNS configuration.
 # Kubernetes cluster name, also will be used as DNS domain
 cluster_name: cluster.local
 # Subdomains of DNS domain to be resolved via /etc/resolv.conf for hostnet pods
 ndots: 2
-# Can be dnsmasq_kubedns, kubedns, manual or none
+# Can be dnsmasq_kubedns, kubedns, coredns, coredns_dual, manual or none
 dns_mode: kubedns
 # Set manual server if using a custom cluster DNS server
 #manual_dns_server: 10.x.x.x
@@ -129,6 +132,7 @@ resolvconf_mode: docker_dns
 deploy_netchecker: false
 # Ip address of the kubernetes skydns service
 skydns_server: "{{ kube_service_addresses|ipaddr('net')|ipaddr(3)|ipaddr('address') }}"
+skydns_server_secondary: "{{ kube_service_addresses|ipaddr('net')|ipaddr(4)|ipaddr('address') }}"
 dnsmasq_dns_server: "{{ kube_service_addresses|ipaddr('net')|ipaddr(2)|ipaddr('address') }}"
 dns_domain: "{{ cluster_name }}"
 

roles/docker/tasks/set_facts_dns.yml

@@ -3,8 +3,10 @@
 - name: set dns server for docker
   set_fact:
     docker_dns_servers: |-
-      {%- if dns_mode == 'kubedns' -%}
+      {%- if dns_mode in ['kubedns', 'coredns'] -%}
         {{ [ skydns_server ] }}
+      {%- elif dns_mode == 'coredns_dual' -%}
+        {{ [ skydns_server ] + [ skydns_server_secondary ] }}
       {%- elif dns_mode == 'dnsmasq_kubedns' -%}
         {{ [ dnsmasq_dns_server ] }}
       {%- elif dns_mode == 'manual' -%}
@@ -24,7 +26,7 @@
 - name: add upstream dns servers (only when dnsmasq is not used)
   set_fact:
     docker_dns_servers: "{{ docker_dns_servers + upstream_dns_servers|default([]) }}"
-  when: dns_mode == 'kubedns'
+  when: dns_mode in ['kubedns', 'coredns', 'coreos_dual']
 
 - name: add global searchdomains
   set_fact:

roles/download/defaults/main.yml

@@ -100,6 +100,9 @@ dnsmasq_image_tag: "{{ dnsmasq_version }}"
 kubedns_version: 1.14.8
 kubedns_image_repo: "gcr.io/google_containers/k8s-dns-kube-dns-amd64"
 kubedns_image_tag: "{{ kubedns_version }}"
+coredns_version: 1.1.0
+coredns_image_repo: "docker.io/coredns/coredns"
+coredns_image_tag: "{{ coredns_version }}"
 dnsmasq_nanny_image_repo: "gcr.io/google_containers/k8s-dns-dnsmasq-nanny-amd64"
 dnsmasq_nanny_image_tag: "{{ kubedns_version }}"
 dnsmasq_sidecar_image_repo: "gcr.io/google_containers/k8s-dns-sidecar-amd64"
@@ -274,25 +277,31 @@ downloads:
     tag: "{{ dnsmasq_image_tag }}"
     sha256: "{{ dnsmasq_digest_checksum|default(None) }}"
   kubedns:
-    enabled: true
+    enabled: "{{ dns_mode in ['kubedns', 'dnsmasq_kubedns'] }}"
     container: true
     repo: "{{ kubedns_image_repo }}"
     tag: "{{ kubedns_image_tag }}"
     sha256: "{{ kubedns_digest_checksum|default(None) }}"
+  coredns:
+    enabled: "{{ dns_mode in ['coredns', 'coredns_dual'] }}"
+    container: true
+    repo: "{{ coredns_image_repo }}"
+    tag: "{{ coredns_image_tag }}"
+    sha256: "{{ coredns_digest_checksum|default(None) }}"
   dnsmasq_nanny:
-    enabled: true
+    enabled: "{{ dns_mode in ['kubedns', 'dnsmasq_kubedns'] }}"
     container: true
     repo: "{{ dnsmasq_nanny_image_repo }}"
     tag: "{{ dnsmasq_nanny_image_tag }}"
     sha256: "{{ dnsmasq_nanny_digest_checksum|default(None) }}"
   dnsmasq_sidecar:
-    enabled: true
+    enabled: "{{ dns_mode in ['kubedns', 'dnsmasq_kubedns'] }}"
     container: true
     repo: "{{ dnsmasq_sidecar_image_repo }}"
     tag: "{{ dnsmasq_sidecar_image_tag }}"
     sha256: "{{ dnsmasq_sidecar_digest_checksum|default(None) }}"
   kubednsautoscaler:
-    enabled: true
+    enabled: "{{ dns_mode in ['kubedns', 'dnsmasq_kubedns'] }}"
     container: true
     repo: "{{ kubednsautoscaler_image_repo }}"
     tag: "{{ kubednsautoscaler_image_tag }}"

roles/kubernetes-apps/ansible/defaults/main.yml

@@ -10,6 +10,9 @@ dns_memory_requests: 70Mi
 kubedns_min_replicas: 2
 kubedns_nodes_per_replica: 10
 
+# CoreDNS
+coredns_replicas: 2
+
 # Images
 kubedns_image_repo: "gcr.io/google_containers/k8s-dns-kube-dns-amd64"
 kubedns_image_tag: "{{ kubedns_version }}"

roles/kubernetes-apps/ansible/tasks/cleanup_dns.yml

@@ -0,0 +1,54 @@
+---
+- name: Kubernetes Apps | Delete old CoreDNS resources
+  kube:
+    name: "coredns"
+    namespace: "{{ system_namespace }}"
+    kubectl: "{{ bin_dir }}/kubectl"
+    resource: "{{ item }}"
+    state: absent
+  with_items:
+    - 'deploy'
+    - 'configmap'
+    - 'svc'
+  tags:
+    - upgrade
+
+- name: Kubernetes Apps | Delete kubeadm CoreDNS
+  kube:
+    name: "coredns"
+    namespace: "{{ system_namespace }}"
+    kubectl: "{{ bin_dir }}/kubectl"
+    resource: "deploy"
+    state: absent
+  when:
+    - kubeadm_enabled|default(false)
+    - kubeadm_init.changed|default(false)
+    - inventory_hostname == groups['kube-master'][0]
+
+- name: Kubernetes Apps | Delete old KubeDNS resources
+  kube:
+    name: "kube-dns"
+    namespace: "{{ system_namespace }}"
+    kubectl: "{{ bin_dir }}/kubectl"
+    resource: "{{ item }}"
+    state: absent
+  with_items:
+    - 'deploy'
+    - 'svc'
+  tags:
+    - upgrade
+
+- name: Kubernetes Apps | Delete kubeadm KubeDNS
+  kube:
+    name: "kube-dns"
+    namespace: "{{ system_namespace }}"
+    kubectl: "{{ bin_dir }}/kubectl"
+    resource: "{{ item }}"
+    state: absent
+  with_items:
+    - 'deploy'
+    - 'svc'
+  when:
+    - kubeadm_enabled|default(false)
+    - kubeadm_init.changed|default(false)
+    - inventory_hostname == groups['kube-master'][0]

roles/kubernetes-apps/ansible/tasks/coredns.yml

@@ -0,0 +1,39 @@
+---
+- name: Kubernetes Apps | Lay Down CoreDNS Template
+  template:
+    src: "{{ item.file }}.j2"
+    dest: "{{ kube_config_dir }}/{{ item.file }}"
+  with_items:
+    - { name: coredns, file: coredns-config.yml, type: configmap }
+    - { name: coredns, file: coredns-sa.yml, type: sa }
+    - { name: coredns, file: coredns-deployment.yml, type: deployment }
+    - { name: coredns, file: coredns-svc.yml, type: svc }
+    - { name: coredns, file: coredns-clusterrole.yml, type: clusterrole }
+    - { name: coredns, file: coredns-clusterrolebinding.yml, type: clusterrolebinding }
+  register: coredns_manifests
+  vars:
+    clusterIP: "{{ skydns_server }}"
+  when:
+    - dns_mode in ['coredns', 'coredns_dual']
+    - inventory_hostname == groups['kube-master'][0]
+    - rbac_enabled or item.type not in rbac_resources
+  tags:
+    - coredns
+
+- name: Kubernetes Apps | Lay Down Secondary CoreDNS Template
+  template:
+    src: "{{ item.src }}.j2"
+    dest: "{{ kube_config_dir }}/{{ item.file }}"
+  with_items:
+    - { name: coredns, src: coredns-deployment.yml, file: coredns-deployment-secondary.yml, type: deployment }
+    - { name: coredns, src: coredns-svc.yml, file: coredns-svc-secondary.yml, type: svc }
+  register: coredns_secondary_manifests
+  vars:
+    clusterIP: "{{ skydns_server_secondary }}"
+    coredns_ordinal_suffix: "-secondary"
+  when:
+    - dns_mode == 'coredns_dual'
+    - inventory_hostname == groups['kube-master'][0]
+    - rbac_enabled or item.type not in rbac_resources
+  tags:
+    - coredns

roles/kubernetes-apps/ansible/tasks/kubedns.yml

@@ -0,0 +1,41 @@
+---
+
+- name: Kubernetes Apps | Lay Down KubeDNS Template
+  template:
+    src: "{{ item.file }}.j2"
+    dest: "{{ kube_config_dir }}/{{ item.file }}"
+  with_items:
+    - { name: kube-dns, file: kubedns-sa.yml, type: sa }
+    - { name: kube-dns, file: kubedns-deploy.yml, type: deployment }
+    - { name: kube-dns, file: kubedns-svc.yml, type: svc }
+    - { name: kubedns-autoscaler, file: kubedns-autoscaler-sa.yml, type: sa }
+    - { name: kubedns-autoscaler, file: kubedns-autoscaler-clusterrole.yml, type: clusterrole }
+    - { name: kubedns-autoscaler, file: kubedns-autoscaler-clusterrolebinding.yml, type: clusterrolebinding }
+    - { name: kubedns-autoscaler, file: kubedns-autoscaler.yml, type: deployment }
+  register: kubedns_manifests
+  when:
+    - dns_mode in ['kubedns','dnsmasq_kubedns']
+    - inventory_hostname == groups['kube-master'][0]
+    - rbac_enabled or item.type not in rbac_resources
+  tags:
+    - dnsmasq
+
+# see https://github.com/kubernetes/kubernetes/issues/45084, only needed for "old" kube-dns
+- name: Kubernetes Apps | Patch system:kube-dns ClusterRole
+  command: >
+    {{ bin_dir }}/kubectl patch clusterrole system:kube-dns
+    --patch='{
+               "rules": [
+                 {
+                   "apiGroups" : [""],
+                   "resources" : ["endpoints", "services"],
+                   "verbs": ["list", "watch", "get"]
+                 }
+               ]
+             }'
+  when:
+    - dns_mode in ['kubedns', 'dnsmasq_kubedns']
+    - inventory_hostname == groups['kube-master'][0]
+    - rbac_enabled and kubedns_version|version_compare("1.11.0", "<", strict=True)
+  tags:
+    - dnsmasq

roles/kubernetes-apps/ansible/tasks/main.yml

@@ -11,66 +11,26 @@
   delay: 2
   when: inventory_hostname == groups['kube-master'][0]
 
-- name: Kubernetes Apps | Delete old kubedns resources
-  kube:
-    name: "kubedns"
-    namespace: "{{ system_namespace }}"
-    kubectl: "{{ bin_dir }}/kubectl"
-    resource: "{{ item }}"
-    state: absent
-  with_items:
-    - 'deploy'
-    - 'svc'
+- name: Kubernetes Apps | Cleanup DNS
+  import_tasks: tasks/cleanup_dns.yml
+  when:
+    - inventory_hostname == groups['kube-master'][0]
   tags:
     - upgrade
 
-- name: Kubernetes Apps | Delete kubeadm kubedns
-  kube:
-    name: "kubedns"
-    namespace: "{{ system_namespace }}"
-    kubectl: "{{ bin_dir }}/kubectl"
-    resource: "deploy"
-    state: absent
+- name: Kubernetes Apps | CoreDNS
+  import_tasks: "tasks/coredns.yml"
   when:
-    - kubeadm_enabled|default(false)
-    - kubeadm_init.changed|default(false)
+    - dns_mode in ['coredns', 'coredns_dual']
     - inventory_hostname == groups['kube-master'][0]
-
-- name: Kubernetes Apps | Lay Down KubeDNS Template
-  template:
-    src: "{{ item.file }}.j2"
-    dest: "{{ kube_config_dir }}/{{ item.file }}"
-  with_items:
-    - { name: kube-dns, file: kubedns-sa.yml, type: sa }
-    - { name: kube-dns, file: kubedns-deploy.yml, type: deployment }
-    - { name: kube-dns, file: kubedns-svc.yml, type: svc }
-    - { name: kubedns-autoscaler, file: kubedns-autoscaler-sa.yml, type: sa }
-    - { name: kubedns-autoscaler, file: kubedns-autoscaler-clusterrole.yml, type: clusterrole }
-    - { name: kubedns-autoscaler, file: kubedns-autoscaler-clusterrolebinding.yml, type: clusterrolebinding }
-    - { name: kubedns-autoscaler, file: kubedns-autoscaler.yml, type: deployment }
-  register: manifests
-  when:
-    - dns_mode != 'none' and inventory_hostname == groups['kube-master'][0]
-    - rbac_enabled or item.type not in rbac_resources
   tags:
-    - dnsmasq
+    - coredns
 
-# see https://github.com/kubernetes/kubernetes/issues/45084, only needed for "old" kube-dns
-- name: Kubernetes Apps | Patch system:kube-dns ClusterRole
-  command: >
-    {{ bin_dir }}/kubectl patch clusterrole system:kube-dns
-    --patch='{
-               "rules": [
-                 {
-                   "apiGroups" : [""],
-                   "resources" : ["endpoints", "services"],
-                   "verbs": ["list", "watch", "get"]
-                 }
-               ]
-             }'
+- name: Kubernetes Apps | KubeDNS
+  import_tasks: "tasks/kubedns.yml"
   when:
-    - dns_mode != 'none' and inventory_hostname == groups['kube-master'][0]
-    - rbac_enabled and kubedns_version|version_compare("1.11.0", "<", strict=True)
+    - dns_mode in ['kubedns', 'dnsmasq_kubedns']
+    - inventory_hostname == groups['kube-master'][0]
   tags:
     - dnsmasq
 
@@ -82,7 +42,10 @@
     resource: "{{ item.item.type }}"
     filename: "{{ kube_config_dir }}/{{ item.item.file }}"
     state: "latest"
-  with_items: "{{ manifests.results }}"
+  with_items:
+    - "{{ kubedns_manifests.results | default({}) }}"
+    - "{{ coredns_manifests.results | default({}) }}"
+    - "{{ coredns_secondary_manifests.results | default({}) }}"
   when:
     - dns_mode != 'none'
     - inventory_hostname == groups['kube-master'][0]

roles/kubernetes-apps/ansible/templates/coredns-clusterrole.yml.j2

@@ -0,0 +1,19 @@
+---
+apiVersion: rbac.authorization.k8s.io/v1beta1
+kind: ClusterRole
+metadata:
+  labels:
+    kubernetes.io/bootstrapping: rbac-defaults
+    addonmanager.kubernetes.io/mode: Reconcile
+  name: system:coredns
+rules:
+- apiGroups:
+  - ""
+  resources:
+  - endpoints
+  - services
+  - pods
+  - namespaces
+  verbs:
+  - list
+  - watch

roles/kubernetes-apps/ansible/templates/coredns-clusterrolebinding.yml.j2

@@ -0,0 +1,18 @@
+---
+apiVersion: rbac.authorization.k8s.io/v1beta1
+kind: ClusterRoleBinding
+metadata:
+  annotations:
+    rbac.authorization.kubernetes.io/autoupdate: "true"
+  labels:
+    kubernetes.io/bootstrapping: rbac-defaults
+    addonmanager.kubernetes.io/mode: EnsureExists
+  name: system:coredns
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: ClusterRole
+  name: system:coredns
+subjects:
+- kind: ServiceAccount
+  name: coredns
+  namespace: {{ system_namespace }}

roles/kubernetes-apps/ansible/templates/coredns-config.yml.j2

@@ -0,0 +1,22 @@
+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: coredns
+  namespace: {{ system_namespace }}
+  labels:
+    addonmanager.kubernetes.io/mode: EnsureExists
+data:
+  Corefile: |
+    .:53 {
+        errors
+        health
+        kubernetes {{ cluster_name }} in-addr.arpa ip6.arpa {
+          pods insecure
+          upstream /etc/resolv.conf
+          fallthrough in-addr.arpa ip6.arpa
+        }
+        prometheus :9153
+        proxy . /etc/resolv.conf
+        cache 30
+    }

roles/kubernetes-apps/ansible/templates/coredns-deployment.yml.j2

@@ -0,0 +1,81 @@
+---
+apiVersion: extensions/v1beta1
+kind: Deployment
+metadata:
+  name: coredns{{ coredns_ordinal_suffix | default('') }}
+  namespace: {{ system_namespace }}
+  labels:
+    k8s-app: coredns{{ coredns_ordinal_suffix | default('') }}
+    kubernetes.io/cluster-service: "true"
+    addonmanager.kubernetes.io/mode: Reconcile
+    kubernetes.io/name: "CoreDNS"
+spec:
+  replicas: {{ coredns_replicas }}
+  strategy:
+    type: RollingUpdate
+    rollingUpdate:
+      maxUnavailable: 0
+      maxSurge: 10%
+  selector:
+    matchLabels:
+      k8s-app: coredns{{ coredns_ordinal_suffix | default('') }}
+  template:
+    metadata:
+      labels:
+        k8s-app: coredns{{ coredns_ordinal_suffix | default('') }}
+      annotations:
+        scheduler.alpha.kubernetes.io/critical-pod: ''
+    spec:
+{% if rbac_enabled %}
+      serviceAccountName: coredns
+{% endif %}
+      tolerations:
+        - key: node-role.kubernetes.io/master
+          effect: NoSchedule
+        - key: "CriticalAddonsOnly"
+          operator: "Exists"
+      containers:
+      - name: coredns
+        image: "{{ coredns_image_repo }}:{{ coredns_image_tag }}"
+        imagePullPolicy: {{ k8s_image_pull_policy }}
+        resources:
+          # TODO: Set memory limits when we've profiled the container for large
+          # clusters, then set request = limit to keep this container in
+          # guaranteed class. Currently, this container falls into the
+          # "burstable" category so the kubelet doesn't backoff from restarting it.
+          limits:
+            memory: {{ dns_memory_limit }}
+          requests:
+            cpu: {{ dns_cpu_requests }}
+            memory: {{ dns_memory_requests }}
+        args: [ "-conf", "/etc/coredns/Corefile" ]
+        volumeMounts:
+        - name: config-volume
+          mountPath: /etc/coredns
+        ports:
+        - containerPort: 53
+          name: dns
+          protocol: UDP
+        - containerPort: 53
+          name: dns-tcp
+          protocol: TCP
+        - containerPort: 9153
+          name: metrics
+          protocol: TCP
+        livenessProbe:
+          httpGet:
+            path: /health
+            port: 8080
+            scheme: HTTP
+          initialDelaySeconds: 60
+          timeoutSeconds: 5
+          successThreshold: 1
+          failureThreshold: 5
+      dnsPolicy: Default
+      volumes:
+        - name: config-volume
+          configMap:
+            name: coredns
+            items:
+            - key: Corefile
+              path: Corefile

roles/kubernetes-apps/ansible/templates/coredns-sa.yml.j2

@@ -0,0 +1,9 @@
+---
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: coredns
+  namespace: {{ system_namespace }}
+  labels:
+    kubernetes.io/cluster-service: "true"
+    addonmanager.kubernetes.io/mode: Reconcile

roles/kubernetes-apps/ansible/templates/coredns-svc.yml.j2

@@ -0,0 +1,22 @@
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: coredns{{ coredns_ordinal_suffix | default('') }}
+  namespace: {{ system_namespace }}
+  labels:
+    k8s-app: coredns{{ coredns_ordinal_suffix | default('') }}
+    kubernetes.io/cluster-service: "true"
+    addonmanager.kubernetes.io/mode: Reconcile
+    kubernetes.io/name: "CoreDNS"
+spec:
+  selector:
+    k8s-app: coredns{{ coredns_ordinal_suffix | default('') }}
+  clusterIP: {{ clusterIP }}
+  ports:
+  - name: dns
+    port: 53
+    protocol: UDP
+  - name: dns-tcp
+    port: 53
+    protocol: TCP

roles/kubernetes/node/templates/kubelet.kubeadm.env.j2

@@ -50,8 +50,10 @@ KUBELET_HOSTNAME="--hostname-override={{ kube_override_hostname }}"
 {% endif %}
 
 {# DNS settings for kubelet #}
-{% if dns_mode == 'kubedns' %}
+{% if dns_mode in ['kubedns', 'coredns'] %}
 {% set kubelet_args_cluster_dns %}--cluster-dns={{ skydns_server }}{% endset %}
+{% elif dns_mode == 'coredns_dual' %}
+{% set kubelet_args_cluster_dns %}--cluster-dns={{ skydns_server }},{{ skydns_server_secondary }}{% endset %}
 {% elif dns_mode == 'dnsmasq_kubedns' %}
 {% set kubelet_args_cluster_dns %}--cluster-dns={{ dnsmasq_dns_server }}{% endset %}
 {% elif dns_mode == 'manual' %}

roles/kubernetes/node/templates/kubelet.standard.env.j2

@@ -42,8 +42,10 @@ KUBELET_HOSTNAME="--hostname-override={{ kube_override_hostname }}"
 --enforce-node-allocatable={{ kubelet_enforce_node_allocatable }} {% endif %}{% endset %}
 
 {# DNS settings for kubelet #}
-{% if dns_mode == 'kubedns' %}
+{% if dns_mode in ['kubedns', 'coredns'] %}
 {% set kubelet_args_cluster_dns %}--cluster-dns={{ skydns_server }}{% endset %}
+{% elif dns_mode == 'coredns_dual' %}
+{% set kubelet_args_cluster_dns %}--cluster-dns={{ skydns_server }},{{ skydns_server_secondary }}{% endset %}
 {% elif dns_mode == 'dnsmasq_kubedns' %}
 {% set kubelet_args_cluster_dns %}--cluster-dns={{ dnsmasq_dns_server }}{% endset %}
 {% elif dns_mode == 'manual' %}

roles/kubernetes/preinstall/tasks/set_resolv_facts.yml

@@ -93,8 +93,10 @@
 - name: pick dnsmasq cluster IP or default resolver
   set_fact:
     dnsmasq_server: |-
-      {%- if dns_mode == 'kubedns' and not dns_early|bool -%}
+      {%- if dns_mode in ['kubedns', 'coredns'] and not dns_early|bool -%}
         {{ [ skydns_server ] + upstream_dns_servers|default([]) }}
+      {%- elif dns_mode == 'coredns_dual' and not dns_early|bool -%}
+        {{ [ skydns_server ] + [ skydns_server_secondary ] + upstream_dns_servers|default([]) }}
       {%- elif dns_mode == 'manual' and not dns_early|bool -%}
         {{ [ manual_dns_server ] + upstream_dns_servers|default([]) }}
       {%- elif dns_early|bool -%}

roles/kubespray-defaults/defaults/main.yaml

@@ -49,6 +49,7 @@ resolvconf_mode: docker_dns
 deploy_netchecker: false
 # Ip address of the kubernetes skydns service
 skydns_server: "{{ kube_service_addresses|ipaddr('net')|ipaddr(3)|ipaddr('address') }}"
+skydns_server_secondary: "{{ kube_service_addresses|ipaddr('net')|ipaddr(4)|ipaddr('address') }}"
 dnsmasq_dns_server: "{{ kube_service_addresses|ipaddr('net')|ipaddr(2)|ipaddr('address') }}"
 dns_domain: "{{ cluster_name }}"