- hosts: all
  gather_facts: no
  ignore_errors: yes
  ignore_unreachable: yes

  vars:
    list: "{{ lookup('dig', ansible_host) }}"

  tasks:

  - debug:
      var: list

  - name: check
    ping:
    register: result

  - debug:
      var: result

  - name: send
    slack:
      domain: *.slack.com
      token:
      color: danger
      channel: #alerts
      msg: "{{ ansible_host }} is unreachable"
    when: result is unreachable


PLAY [all] ****************************************************************************************************************************************************************************************************

TASK [debug] ******************************************************************************************************************************************************************************************************
ok: [host1] => {
    "list": "*.*.0.99"
}
ok: [host0] => {
    "list": "*.*.0.98"
}

TASK [check] ******************************************************************************************************************************************************************************************************
ok: [host0]
fatal: [host1]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: ssh: connect to host *.*.0.99 port 922: No route to host", "skip_reason": "Host worker1 is unreachable", "unreachable": true}

TASK [debug] ******************************************************************************************************************************************************************************************************
ok: [host0] => {
    "result": {
        "ansible_facts": {
            "discovered_interpreter_python": "/usr/bin/python"
        },
        "changed": false,
        "failed": false,
        "ping": "pong"
    }
}
ok: [host1] => {
    "result": {
        "changed": false,
        "msg": "Failed to connect to the host via ssh: ssh: connect to host *.*.0.99 port 922: No route to host",
        "unreachable": true
    }
}

TASK [send] *******************************************************************************************************************************************************************************************************
skipping: [host0]
fatal: [host1]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: ssh: connect to host *.*.0.99 port 922: No route to host", "skip_reason": "Host worker1 is unreachable", "unreachable": true}

PLAY RECAP ********************************************************************************************************************************************************************************************************
host0                    : ok=3    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0
host1                    : ok=2    changed=0    unreachable=2    failed=0    skipped=2    rescued=0    ignored=0