salt,docs: Allow to manage number of CoreDNS replica

Refs: #3574

CHANGELOG.md

@@ -6,9 +6,10 @@
   when observing the cluster state (used in the UI Dashboard page)
   (PR[#3540](https://github.com/scality/metalk8s/pull/3540))
 
-- Allow to manage soft and hard `podAntiAffinity` for `CoreDNS` from Bootstrap
-  configuration file, with a default soft anti-affinity on hostname, so that if
-  it's possible each `CoreDNS` pods will sit on different infra node
+- Allow to manage number of replicas and, soft and hard `podAntiAffinity` for
+  `CoreDNS` from Bootstrap configuration file, with a default soft
+  anti-affinity on hostname, so that if it's possible each `CoreDNS`
+  pods will sit on different infra node
   (PR[#](https://github.com/scality/metalk8s/pull/))
 
 ### Removals

docs/installation/bootstrap.rst

@@ -71,6 +71,7 @@ Configuration
           featureGates:
             <feature_gate_name>: True
         coreDNS:
+          replicas: 2
           podAntiAffinity:
             hard: []
             soft:
@@ -171,12 +172,13 @@ defaults kubernetes configuration.
   configure the corresponding entries in the
   ``kubernetes.apiServer.featureGates`` mapping.
 
-  If you want to override the default ``coreDNS`` podAntiAffinity, by default
-  MetalK8s use soft podAntiAffinity on hostname so that if it's possible
-  ``coreDNS`` pods will be spread on different infra nodes.
-  If you have more infra node than ``coreDNS`` replicas (default is 2), you
-  should set hard podAntiAffinity on hostname so that you are sure that
-  ``coreDNS`` pods sit on different node, to do so:
+  If you want to override the default ``coreDNS`` podAntiAffinity or number of
+  replicas, by default MetalK8s deploy 2 replicas and use soft podAntiAffinity
+  on hostname so that if it's possible ``coreDNS`` pods will be spread on
+  different infra nodes.
+  If you have more infra node than ``coreDNS`` replicas, you should set hard
+  podAntiAffinity on hostname so that you are sure that ``coreDNS`` pods sit
+  on different node, to do so:
 
     .. code-block:: yaml
 

salt/metalk8s/kubernetes/coredns/deployed.sls

@@ -3,9 +3,12 @@
 
 {%- set cluster_dns_ip = salt.metalk8s_network.get_cluster_dns_ip() %}
 
+{%- set pillar_coredns = pillar.kubernetes.get("coreDNS", {}) %}
+
+{%- set replicas = pillar_coredns.get("replicas") or 2 %}
 {%- set label_selector = {"k8s-app": "kube-dns"} %}
 
-{%- set pillar_affinities = pillar.kubernetes.get("coreDNS", {}).get("podAntiAffinity", {}) %}
+{%- set pillar_affinities = pillar_coredns.get("podAntiAffinity", {}) %}
 {#- NOTE: The default podAntiAffinity is a soft anti-affinity on hostname #}
 {%- set soft_affinities = pillar_affinities.get("soft") or [{"topologyKey": "kubernetes.io/hostname"}] %}
 {%- set hard_affinities = pillar_affinities.get("hard") or [] %}
@@ -82,6 +85,7 @@ Create coredns deployment:
     - defaults:
         label_selector: {{ label_selector | tojson }}
         affinity: {{ affinity | tojson }}
+        replicas: {{ replicas }}
 
     - require:
       - metalk8s_kubernetes: Create coredns ConfigMap

salt/metalk8s/kubernetes/coredns/files/coredns-deployment.yaml.j2

@@ -13,7 +13,7 @@ metadata:
     app.kubernetes.io/part-of: metalk8s
     app.kubernetes.io/managed-by: salt
 spec:
-  replicas: 2
+  replicas: {{ replicas }}
   strategy:
     type: RollingUpdate
     rollingUpdate: