根据多个条件选择主机执行任务

Question

使用 Ansible v2.9.12

想象一个游戏中有 4 个主机，具有以下变量：

# host1
my_var:
  one: true
  two: master

# host2
my_var:
  one: false
  two: master

# host3
my_var:
  one: false
  two: master

# host4
my_var:
  one: false
  two: arbiter

我想在单个主机上执行一个任务，该主机具有 my_var.two == 'master' 并将 my_var.one 设置为 false。在这种情况下，它将与 host2 或 host3 相关。

现在，这行不通了：

- shell: echo
  when: 
    - my_var.two == 'master'
    - not my_var.one
   run_once: true

因为 Ansible 仅在组中的第一台主机上执行任务，这很可能与 host1 相关，这是不受欢迎的。我也在摆弄the answer described in my previous question，这有点相关，但无济于事。

Answer 1

没有什么能阻止你在剧本中进行多次剧本：

- hosts: all
  gather_facts: no
      
  tasks:
    - debug: 
        msg: "{{ my_var }}"

- hosts: host2
  gather_facts: no
      
  tasks:
    - debug: 
        msg: "{{ my_var }}"
      # ^--- Off course, now the when become superfluous, 
      #      since we target a host that we know have those conditions

- hosts: all
  gather_facts: no

  tasks:
    - debug:
        msg: "Keep on going with all hosts"

回顾一下：

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

TASK [debug] ********************************************************************************************************
ok: [host1] => {
    "msg": {
        "one": true,
        "two": "master"
    }
}
ok: [host2] => {
    "msg": {
        "one": false,
        "two": "master"
    }
}
ok: [host3] => {
    "msg": {
        "one": false,
        "two": "master"
    }
}
ok: [host4] => {
    "msg": {
        "one": false,
        "two": "arbiter"
    }
}

PLAY [host2] ********************************************************************************************************

TASK [debug] ********************************************************************************************************
ok: [host2] => {
    "msg": {
        "one": false,
        "two": "master"
    }
}

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

TASK [debug] ********************************************************************************************************
ok: [host1] => {
    "msg": "Keep on going with all hosts"
}
ok: [host2] => {
    "msg": "Keep on going with all hosts"
}
ok: [host3] => {
    "msg": "Keep on going with all hosts"
}
ok: [host4] => {
    "msg": "Keep on going with all hosts"
}

PLAY RECAP **********************************************************************************************************
host1                      : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
host2                      : ok=3    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
host3                      : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
host4                      : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0 

---

或者，对于更动态的解决方案，您可以选择正确的主机，通过魔术变量 hostvars 循环访问主机变量，然后使用 delegate_to 将任务委托给该主机。

鉴于剧本：

- hosts: all
  gather_facts: no
      
  tasks:
    - set_fact: 
        host_master_not_one: "{{ item }}"
      when:
        - host_master_not_one is not defined
        - not hostvars[item].my_var.one
        - "'master' == hostvars[item].my_var.two"
      run_once: true
      loop: "{{ ansible_play_hosts }}" 
    
    - debug: 
        msg: "Running only once, on host {{ host_master_not_one }}"
      delegate_to: "{{ host_master_not_one }}"
      run_once: true

它给出了回顾：

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

TASK [set_fact] *****************************************************************************************************
skipping: [host1] => (item=host1) 
ok: [host1] => (item=host2)
skipping: [host1] => (item=host3) 
skipping: [host1] => (item=host4) 

TASK [debug] ********************************************************************************************************
ok: [host1 -> host2] => {
    "msg": "Running only once, on host host2"
}

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

此回顾的重要部分是 [host1 -> host2]，它表示任务已被委派，因此在 host2 上运行。

---

甚至，在同样的思路上，跳过与具有上述条件的主机不匹配的主机：

- hosts: all
  gather_facts: no
      
  tasks:
    - set_fact: 
        host_master_not_one: "{{ item }}"
      when:
        - host_master_not_one is not defined
        - not hostvars[item].my_var.one
        - "'master' == hostvars[item].my_var.two"
      run_once: true
      loop: "{{ ansible_play_hosts }}" 
    
    - debug: 
        msg: "Running only once, on host {{ host_master_not_one }}"
      when: inventory_hostname == host_master_not_one

回顾一下：

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

TASK [set_fact] *****************************************************************************************************
skipping: [host1] => (item=host1) 
ok: [host1] => (item=host2)
skipping: [host1] => (item=host3) 
skipping: [host1] => (item=host4) 

TASK [debug] ********************************************************************************************************
skipping: [host1]
ok: [host2] => {
    "msg": "Running only once, on host host2"
}
skipping: [host3]
skipping: [host4]

PLAY RECAP **********************************************************************************************************
host1                      : ok=1    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0   
host2                      : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
host3                      : ok=0    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0   
host4                      : ok=0    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0