Add role for adding docker nodes to swarm

roles/swarm/tasks/check.yaml

@@ -0,0 +1,69 @@
+---
+- name: Check cluster swarm status
+  run_once: true
+  block:
+    - name: Fetch cluster server swarm info
+      delegate_to: "{{ item }}"
+      ansible.builtin.command:
+        cmd: !unsafe docker info --format '{{json .Swarm}}'
+      changed_when: false
+      register: _docker_cluster_swarm_state_raw
+      loop: "{{ groups.cluster }}"
+
+    - name: Process cluster server swarm info
+      vars:
+        _docker_cluster_swarm_state: {}
+      ansible.builtin.set_fact:
+        _docker_cluster_swarm_state: "{{ _docker_cluster_swarm_state | combine({item.item: (item.stdout | from_json)}) }}"
+      loop: "{{ _docker_cluster_swarm_state_raw.results }}"
+      loop_control:
+        label: "{{ item.item }}"
+
+    - name: Identify swarm managers
+      vars:
+        _docker_cluster_swarm_managers: []
+      when: item.value.LocalNodeState == 'active' and item.value.ControlAvailable
+      ansible.builtin.set_fact:
+        _docker_cluster_swarm_managers: "{{ _docker_cluster_swarm_managers + [item.key] }}"
+      loop: "{{ _docker_cluster_swarm_state | dict2items }}"
+      loop_control:
+        label: "{{ item.key }}"
+
+    - name: Check that swarm managers were discovered
+      ansible.builtin.assert:
+        that:
+          - _docker_cluster_swarm_managers
+        fail_msg: >-
+          ERROR: None of the member cluster servers ({{ groups.cluster | join(', ') }}) are joined to
+          a docker swarm or is a swarm manager. Please join at least one cluster server to a swarm and
+          promote it to swarm manager
+        success_msg: >-
+          Identified {{ _docker_cluster_swarm_managers | count }} swarm managers
+          ({{ _docker_cluster_swarm_managers | join(', ') }})
+
+    - name: Determine swarm manager cluster IDs
+      vars:
+        _docker_cluster_swarm_manager_cluster_ids: []
+      ansible.builtin.set_fact:
+        _docker_cluster_swarm_manager_cluster_ids: "{{ _docker_cluster_swarm_manager_cluster_ids + [_docker_cluster_swarm_state[item].Cluster.ID] }}"
+      loop: "{{ _docker_cluster_swarm_managers }}"
+
+    - name: Check swarm managers are part of the same swarm
+      ansible.builtin.assert:
+        that:
+          - _docker_cluster_swarm_manager_cluster_ids | unique | count == 1
+        fail_msg: >-
+          ERROR: Swarm managers ({{ _docker_cluster_swarm_managers | join(', ') }}) appear to be
+          joined to different swarms
+          (IDs {{ _docker_cluster_swarm_manager_cluster_ids | join(', ') }})
+        success_msg: >-
+          Swarm managers are joined to swarm with ID
+          {{ _docker_cluster_swarm_manager_cluster_ids[0] }}
+
+    - name: Determine swarm manager to use for host configuration
+      ansible.builtin.set_fact:
+        _docker_swarm_manager: "{{ _docker_cluster_swarm_managers[0] }}"
+
+- name: Determine whether host needs to be added to the swarm
+  ansible.builtin.set_fact:
+    _docker_swarm_needs_join: "{{ not _docker_cluster_swarm_state[inventory_hostname].Cluster.ID | default('') == _docker_cluster_swarm_manager_cluster_ids[0] }}"