Ansible多主机条件判断异常：标准Cron任务未按预期排除指定主机

我正尝试配置两种不同的cron任务：部分主机需执行标准cron任务，其余主机执行故障转移cron任务，同时要将somescript.sh复制到所有主机。

主机清单片段 #

[zaspare]
host01.example.com
host02.example.com
host03.example.com
host04.example.com
host05.example.com
host06.example.com
host07.example.com
host08.example.com

原Playbook（存在问题） #

---

- name: Updating somescript
  hosts: zaspare
  become: yes

  tasks:


  - name: Copy somescript.sh script to /usr/local/bin
    copy:
      src: somescript.sh
      dest: /usr/local/bin/
      owner: root
      group: root
      mode: 0755
      
  - name: Setup standard crontab for somescript    
    cron:
      name: Run somescript.sh
      job: /usr/local/bin/somescript.sh {{ inventory_hostname }} false 
      cron_file: somescript
      user: root
      minute: "10"
      hour: "22"
    when: inventory_hostname != "host01.example.com" or 
          inventory_hostname != "host02.example.com" or
          inventory_hostname != "host03.example.com" or
          inventory_hostname != "host04.example.com" or
          inventory_hostname != "host05.example.com"       

  - name: Setup failover crontab for somescript    
    cron:
      name: Run somescript.sh
      job: /usr/local/bin/somescript.sh {{ inventory_hostname }} true 
      cron_file: somescript
      user: root
      minute: "10"
      hour: "22"
    when: inventory_hostname == "host01.example.com" or 
          inventory_hostname == "host02.example.com" or
          inventory_hostname == "host03.example.com" or
          inventory_hostname == "host04.example.com" or
          inventory_hostname == "host05.example.com"

执行结果异常 #

TASK [Setup standard crontab for somescript]******************************
changed: [host06.example.com]
changed: [host07.example.com]
changed: [host01.example.com]
changed: [host08.example.com]
changed: [host02.example.com]
changed: [host04.example.com]
changed: [host03.example.com]
changed: [host05.example.com]

TASK [Setup failover crontab for somescript]******************************
skipping: [host06.example.com]
skipping: [host07.example.com]
skipping: [host08.example.com]
changed: [host01.example.com]
changed: [host02.example.com]
changed: [host03.example.com]
changed: [host04.example.com]
changed: [host05.example.com]

单主机排除时Playbook可正常工作，但多主机排除时标准Cron任务在所有主机上都执行了。

问题出在逻辑运算符使用错误：

你在标准Cron任务的when条件里用了or，但实际需要的是and。举个例子，对于host01.example.com，inventory_hostname != "host02.example.com"这个条件是成立的，所以整个or组合的结果为真，导致任务执行。

正确的逻辑应该是：仅当主机名不是host01到host05中的任何一个时，才执行标准Cron任务，也就是所有的!=条件必须同时满足，所以要用and连接。

另外，更简洁且易维护的写法是把需要排除的主机放到一个列表里，用not in来判断：

修正后的Playbook #

---

- name: Updating somescript
  hosts: zaspare
  become: yes

  vars:
    failover_hosts:
      - host01.example.com
      - host02.example.com
      - host03.example.com
      - host04.example.com
      - host05.example.com

  tasks:

  - name: Copy somescript.sh script to /usr/local/bin
    copy:
      src: somescript.sh
      dest: /usr/local/bin/
      owner: root
      group: root
      mode: 0755
      
  - name: Setup standard crontab for somescript    
    cron:
      name: Run somescript.sh
      job: /usr/local/bin/somescript.sh {{ inventory_hostname }} false 
      cron_file: somescript
      user: root
      minute: "10"
      hour: "22"
    when: inventory_hostname not in failover_hosts       

  - name: Setup failover crontab for somescript    
    cron:
      name: Run somescript.sh
      job: /usr/local/bin/somescript.sh {{ inventory_hostname }} true 
      cron_file: somescript
      user: root
      minute: "10"
      hour: "22"
    when: inventory_hostname in failover_hosts

这种写法不仅逻辑清晰，后续要添加或移除故障转移主机时，只需要修改failover_hosts变量即可，不需要调整条件判断语句。

内容的提问来源于stack exchange，提问作者Bianca_K