var node_labels as string (#4764)

docs/vars.md

@@ -117,11 +117,13 @@ Stack](https://github.com/kubernetes-sigs/kubespray/blob/master/docs/dns-stack.m
   from the kube-apiserver when the certificate expiration approaches.
 * *node_labels* - Labels applied to nodes via kubelet --node-labels parameter.
   For example, labels can be set in the inventory as variables or more widely in group_vars.
-  *node_labels* must be defined as a dict:
+  *node_labels* can be defined either as a dict or a comma-separaded labels string:
 ```
 node_labels:
   label1_name: label1_value
   label2_name: label2_value
+
+node_labels: "label1_name=label1_value,label2_name=label2_value"
 ```
 * *node_taints* - Taints applied to nodes via kubelet --register-with-taints parameter.
   For example, taints can be set in the inventory as variables or more widely in group_vars.

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

@@ -91,11 +91,16 @@ KUBELET_HOSTNAME="--hostname-override={{ kube_override_hostname }}"
 {% endif %}
 
 {% set inventory_node_labels = [] %}
-{% if node_labels is defined and node_labels is mapping %}
-{%   for labelname, labelvalue in node_labels.items() %}
-{%     set dummy = inventory_node_labels.append('%s=%s'|format(labelname, labelvalue)) %}
-{%   endfor %}
-{% endif %}
+{% if node_labels is defined %}
+{%   if node_labels is mapping %}
+{%     for labelname, labelvalue in node_labels.items() %}
+{%       set dummy = inventory_node_labels.append('%s=%s'|format(labelname, labelvalue)) %}
+{%     endfor %}
+{%   else %}
+{%     for label in node_labels.split(",") %}
+{%       set dummy = inventory_node_labels.append(label) %}
+{%     endfor %}
+{%   endif %}
 {% set all_node_labels = role_node_labels + inventory_node_labels %}
 
 {# Kubelet node taints for gpu #}