set_fact or shell?

gistfile1.yml

- name: If undefined set bootstrap to the first node of the cluster
  set_fact:
    bootstrap: "{{ groups[cluster_name]|first }}"
  when: bootstrap == False or bootstrap is not defined
  tags:
    - couchbase
    - bootstrap

- name: Check if the current machine is part of the cluster
  shell: >
    {{ couchbase_cmd }} server-list \
      -c {{ hostvars[bootstrap]['ansible_' + private_interface]['ipv4']['address'] }}:8091 \
      -u {{ admin_user }} \
      -p {{ admin_password }} \
      | grep {{ hostvars[inventory_hostname]['ansible_' + private_interface]['ipv4']['address'] }}
  ignore_errors: True
  register: is_member
  tags:
    - couchbase
    - bootstrap

- name: Add nodes to the cluster
  shell: >
    {{ couchbase_cmd }} server-add \
      -c {{ hostvars[bootstrap]['ansible_' + private_interface]['ipv4']['address'] }}:8091 \
      -u {{ admin_user }} \
      -p {{ admin_password }} \
      --server-add={{ hostvars[inventory_hostname]['ansible_' + private_interface]['ipv4']['address'] }}:8091 \
      --server-add-username={{ admin_user }} \
      --server-add-password={{ admin_password }}
  when: is_member.rc != 0
  notify:
    - Rebalance the cluster
  tags:
    - couchbase
    - bootstrap