'delegate_to' the IP address. Works when using private IPs.

defaults/main.yml

@@ -12,6 +12,7 @@ docker_swarm_allowed_hosts:
 
 # Set this to one of the manager hostnames to be able to initialize the cluster
 docker_swarm_manager_main_node_hostname: localhost
+docker_swarm_manager_main_node_address: 127.0.0.1
 # Set this on one of the masters
 docker_swarm_manager_main_node: False
 

tasks/swarm_mgr.yml

@@ -27,7 +27,7 @@
       cacheable: True
 
   when: docker_swarm_manager
-  delegate_to: '{{ docker_swarm_manager_main_node_hostname }}'
+  delegate_to: '{{ docker_swarm_manager_main_node_address }}'
   tags: [ 'docker', 'docker_swarm' ]
 
 - block:
@@ -46,7 +46,7 @@
 - block:
   - name: Set the swarm manager nodes availability. Default 'drain'
     docker_node:
-      hostname: '{{ ansible_hostname }}'
+      hostname: '{{ ansible_fqdn }}'
       availability: '{{ docker_swarm_manager_availability }}'
 
   when: docker_swarm_manager | bool

tasks/swarm_node.yml

@@ -39,7 +39,7 @@
       availability: '{{ docker_swarm_node_availability }}'
 
   when: docker_swarm_node | bool
-  delegate_to: '{{ docker_swarm_manager_main_node_hostname }}'
+  delegate_to: '{{ docker_swarm_manager_main_node_address }}'
   tags: [ 'docker', 'docker_swarm', 'docker_swarm_worker_nodes', 'docker_swarm_worker_nodes_availability' ]
 
 - name: Manage labels
@@ -54,5 +54,5 @@
     with_items: '{{ docker_node_labels }}'
 
   when: docker_swarm_node | bool
-  delegate_to: '{{ docker_swarm_manager_main_node_hostname }}'
+  delegate_to: '{{ docker_swarm_manager_main_node_address }}'
   tags: [ 'docker', 'docker_swarm', 'docker_swarm_worker_nodes', 'docker_nodes_labels' ]