Document how to use kubeadm patches

docs/ansible/vars.md

@@ -337,6 +337,13 @@ in the form of dicts of key-value pairs of configuration parameters that will be
 * *kube_kubeadm_controller_extra_args*
 * *kube_kubeadm_scheduler_extra_args*
 
+### Kubeadm patches
+
+When extra flags are not sufficient and there is a need to further customize kubernetes components,
+[kubeadm patches](https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/control-plane-flags/#patches)
+can be used.
+You should use the [`kubeadm_patches` variable](../../roles/kubernetes/kubeadm_common/defaults/main.yml) for that purpose.
+
 ## App variables
 
 * *helm_version* - Only supports v3.x. Existing v2 installs (with Tiller) will not be modified and need to be removed manually.

inventory/sample/group_vars/k8s_cluster/k8s-cluster.yml

@@ -366,11 +366,25 @@ auto_renew_certificates: false
 # First Monday of each month
 # auto_renew_certificates_systemd_calendar: "Mon *-*-1,2,3,4,5,6,7 03:{{ groups['kube_control_plane'].index(inventory_hostname) }}0:00"
 
-# kubeadm patches path
-kubeadm_patches:
-  enabled: false
-  source_dir: "{{ inventory_dir }}/patches"
-  dest_dir: "{{ kube_config_dir }}/patches"
+kubeadm_patches_dir: "{{ kube_config_dir }}/patches"
+kubeadm_patches: []
+# See https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/control-plane-flags/#patches
+# Correspondance with this link
+# patchtype = type
+# target = target
+# suffix -> managed automatically
+# extension -> always "yaml"
+# kubeadm_patches:
+# - target: kube-apiserver|kube-controller-manager|kube-scheduler|etcd|kubeletconfiguration
+#   type: strategic(default)|json|merge
+#   patch:
+#    metadata:
+#      annotations:
+#        example.com/test: "true"
+#      labels:
+#        example.com/prod_level: "{{ prod_level }}"
+# - ...
+# Patches are applied in the order they are specified.
 
 # Set to true to remove the role binding to anonymous users created by kubeadm
 remove_anonymous_access: false

inventory/sample/patches/kube-controller-manager+merge.yaml

----
-apiVersion: v1
-kind: Pod
-metadata:
-  name: kube-controller-manager
-  annotations:
-    prometheus.io/scrape: 'true'
-    prometheus.io/port: '10257'

inventory/sample/patches/kube-scheduler+merge.yaml

----
-apiVersion: v1
-kind: Pod
-metadata:
-  name: kube-scheduler
-  annotations:
-    prometheus.io/scrape: 'true'
-    prometheus.io/port: '10259'

roles/kubernetes/kubeadm_common/defaults/main.yml

 ---
 kubeadm_patches_dir: "{{ kube_config_dir }}/patches"
 kubeadm_patches: []
+# See https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/control-plane-flags/#patches
+# Correspondance with this link
+# patchtype = type
+# target = target
+# suffix -> managed automatically
+# extension -> always "yaml"
 # kubeadm_patches:
 # - target: kube-apiserver|kube-controller-manager|kube-scheduler|etcd|kubeletconfiguration
 #   type: strategic(default)|json|merge