---
- name: Test play
  hosts: my-hosts
  tasks:
    - name: Get number of containers
      shell:
        cmd: docker ps | wc -l
      register: container_num

    - name: Debug
      debug:
        var: container_num.stdout

    - name: Construct inventory
      add_host:
        name: "{{ item }}"
        group: filtered-machines
      loop: "{{ ansible_play_hosts }}"
      when: hostvars[item].container_num.stdout | int > 1

    - name: Run on filtered hosts
      debug:
        var: ansible_hostname
      when: inventory_hostname in groups['filtered-machines']