Define k8s_cluster dynamically

This allows inventories to not define the k8s_cluster group manually.

playbooks/boilerplate.yml

@@ -2,7 +2,9 @@
 - name: Check ansible version
   import_playbook: ansible_version.yml
 
-# These are inventory compatibility tasks to ensure we keep compatibility with old style group names
+# These are inventory compatibility tasks with two purposes:
+# - to ensure we keep compatibility with old style group names
+# - to reduce inventory boilerplate (defining parent groups / empty groups)
 
 - name: Add kube-master nodes to kube_control_plane
   hosts: kube-master
@@ -22,15 +24,6 @@
       group_by:
         key: 'kube_node'
 
-- name: Add k8s-cluster nodes to k8s_cluster
-  hosts: k8s-cluster
-  gather_facts: false
-  tags: always
-  tasks:
-    - name: Add nodes to k8s_cluster group
-      group_by:
-        key: 'k8s_cluster'
-
 - name: Add calico-rr nodes to calico_rr
   hosts: calico-rr
   gather_facts: false
@@ -40,6 +33,15 @@
       group_by:
         key: 'calico_rr'
 
+- name: Define k8s_cluster group
+  hosts: kube_node:kube_control_plane:calico_rr
+  gather_facts: false
+  tags: always
+  tasks:
+    - name: Add nodes to k8s_cluster group
+      group_by:
+        key: 'k8s_cluster'
+
 - name: Add no-floating nodes to no_floating
   hosts: no-floating
   gather_facts: false

tests/cloud_playbooks/roles/packet-ci/templates/inventory.j2

@@ -96,10 +96,3 @@ instance-2
 instance-3
 instance-4
 {% endif %}
-
-[k8s_cluster:children]
-kube_node
-kube_control_plane
-calico_rr
-
-[calico_rr]