ansible中when条件表达式in的错误

项目场景：

创建三台RedHat虚拟主机，配置ip，本地yum（rhel-8.2-x86_64-dvd.iso ），关闭防火墙和SELinux；方便管理分别命名为ansible，node1，node2。安装ansible_soft.tar.gz，配置ansible，主机清单如下

[test]
node[1:2]

利用alice（普通用户，权限为alice ALL=(ALL) NOPASSWD:ALL）角色解决此问题。

创建名叫hard的角色，该角色可以安装、启动、开机自启数据库mariadb服务，还准备了动态文件xyz.j2,
里面是变量“主机名-ip”的格式，调用hard角色就能将这个文件拷贝到被控主机的/root中并命名xyz.txt，但需要配合when判断，只有主机名包含"node"字符串的主机才拷贝。

---

问题描述

Playbook（剧本）写到需要配合when判断，只有主机名包含"node"字符串的主机才拷贝。 问题出现了。

[alice@ansible ansible]$ sudo ansible-playbook inst_mariadb_tem.yml
ERROR! Syntax Error while loading YAML.
  did not find expected key

The error appears to be in '/root/ansible/roles/hard/tasks/main.yml': line 16, column 16, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

#  when: "'node' in ansible_hostname"
  when: 'node' in ansible_hostname
               ^ here
This one looks easy to fix. It seems that there is a value started
with a quote, and the YAML parser is expecting to see the line ended
with the same kind of quote. For instance:

    when: "ok" in result.stdout

Could be written as:

   when: '"ok" in result.stdout'

Or equivalently:

   when: "'ok' in result.stdout"
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此时的roles/hard/tasks/main.yml文件中的引起错误

 when: 'node' in ansible_hostname
1

---

按照报错提示改为

 when: "'node' in ansible_hostname.stdout"
1

以为错误改完了，没想到

fatal: [node2]: FAILED! => {"msg": "The conditional check ''node' in ansible_hostname.stdout' failed.
 The error was: error while evaluating conditional ('node' in ansible_hostname.stdout): 
 Unable to look up a name or access an attribute in template string 
 ({% if 'node' in ansible_hostname.stdout %} True {% else %} False {% endif %}).\n
 Make sure your variable name does not contain invalid characters like '-': 
 argument of type 'AnsibleUndefined' is not iterable\n\nThe error appears to be in 
 '/root/ansible/roles/hard/tasks/main.yml': line 11, column 3, 
 but may\nbe elsewhere in the file depending on the exact syntax problem.\n\n
 The offending line appears to be:\n\n    
 enabled: yes\n- name: 拷贝到被控主机的/root中并命名xyz.txt\n  ^ here\n"}
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解决方案：

我已经要崩溃了，这个错误已经改了两个小时了，🤯🤯🤯！！！！！！！！！！
开始找关于ansible when条件的资料，Ansible 系列之条件判断，种种表明我的是根据他的写的，之后也是根据报错改的，但是但是但是但是就是不对。
濒临放弃的时候将.stdout删除，竟然竟然竟然对了

 when: "'node' in ansible_hostname"
1

第一次时距离答案差一对双引号,
第二次时距离答案多.stdout.
绝望，绝望，绝望😱😱😱。

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原因分析：

其实到目前我都没有真正的理解为什么是这样的，现在只能归咎为自己关于ansible的when条件的理解，练习，语法不知道。一定要认真学习，认真学习，不要认为自己会点就可以不走心，不同的环境，设备版本都会有区别
不抛弃不放弃哦，加油！

这题的完整解答为

[root@ansible ansible]$ sudo ansible-galaxy init roles/hard
[root@ansible ansible]$ sudo vim roles/hard/templates/xyz.j2
{{ansible_hostname}}-{{ansible_all_ipv4_addresses}}
[root@ansible ansible]$ sudo vim roles/hard/tasks/main.yml
---
# tasks file for roles/hard
- name: install mariadb and mariadb-server
  yum:
    name: mariadb-server
- name: start and enabled service
  service:
    name: mariadb
    state: started
    enabled: yes
- name: 拷贝到被控主机的/root中并命名xyz.txt
  template:
    src: xyz.j2
    dest: /root/xyz.txt
  when: "'node' in ansible_hostname" 
[alice@ansible ansible]$ sudo vim inst_mariadb_tem.yml
---
- name: homework
  hosts: test
  roles:
    - hard
	
[alice@ansible ansible]$ sudo ansible-playbook inst_mariadb_tem.yml
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