Add a test for the host layout selection

Change-Id: I80b6917555bdfc8b6b4d8b02a10d815ed1d9cbc1

elk_metrics_6x/tests/testLayout.yml

@@ -0,0 +1,45 @@
+---
+- name: Test host layout
+  hosts: localhost
+  become: true
+
+  vars:
+    storage_node_count: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
+    expected_masters:   [1, 1, 3, 3, 3, 3, 3, 5, 5,  5,  5,  7,  7,  7,  7,  9,  9,  9,  9, 11]
+
+  tasks:
+
+    # the elasticserch cluster elects one master from all those which are marked as master-eligible
+    # 1 node cluster can only have one master
+    # 2 node clusters have 1 master-eligable nodes to avoid split-brain
+    # 3 node clusters have 3 master-eligable nodes
+    # >3 node clusters have (nodes // 2) eligable masters rounded up to the next odd number
+    - name: Master node count fact
+      set_fact:
+        master_node_count: |-
+          {% set masters = 0 %}
+          {% if (item | int) < 3 %}
+          {%   set masters = 1 %}
+          {% elif (item | int) == 3 %}
+          {%   set masters = 3 %}
+          {% else %}
+          {%   set masters = (item | int ) // 2 %}
+          {%   if ((masters | int) % 2 == 0) %}
+          {%     set masters = (masters | int) + 1 %}
+          {%   endif %}
+          {% endif %}
+          {{ masters }}
+      with_items: "{{ storage_node_count }}"
+      register: computed_masters
+
+    - name: Gather results
+      set_fact:
+        masters: "{{ masters|default([]) + [ { 'nodes': item.item, 'masters': (item.ansible_facts.master_node_count|int) } ] }}"
+      with_items: "{{ computed_masters.results }}"
+
+    - name: Check results
+      assert:
+        that: item.0 == item.1.masters
+      with_together:
+        - "{{ expected_masters }}"
+        - "{{ masters }}"