The mei_generator_db_executor is optional.

defaults/main.yml

@@ -5,4 +5,4 @@ mei_generator_compose_url: 'https://raw.githubusercontent.com/CMCC-Foundation/bl
 #cmmc_mysql_root_password: 'set it in a vault file'
 #cmmc_mysql_password: 'set it in a vault file'
 #mei_generator_db_constraints: '[node.labels.db_data==mei_generator]'
-mei_generator_db_executor: 'docker-exec1.int.d4science.net'
+#mei_generator_db_executor: 'docker-exec1.int.d4science.net'

tasks/main.yml

@@ -34,6 +34,7 @@
         labels:
           mei_generator_db_data: 'bc_mei_generator'
         labels_state: 'merge'
+      when: mei_generator_db_executor is defined
 
     - name: Start the MEI Generator stack
       docker_stack: