环境
- 管理节点：Ubuntu 22.04
- 控制节点：CentOS 8
- Ansible：2.15.6
handler
当任务结果产生变化时，通过 notify 通知handler做相应处理。
一个简单例子
---
- hosts: alltasks:- name: task1debug:msg: "I am task1"changed_when: truenotify:- handler1handlers:- name: handler1debug:msg: "I am handler1"
运行结果如下：
TASK [task1] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task1"
}RUNNING HANDLER [handler1] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler1"
}
注意：只有task产生变化时，才会触发notify。由于debug语句不产生变化，所以指定 changed_when: true ，强制task1产生变化。
一个复杂例子
---
- hosts: alltasks:- name: task1debug:msg: "I am task1"- name: task2debug:msg: "I am task2"changed_when: truenotify:- handler2- handler1- name: task3debug:msg: "I am task3"handlers:- name: handler1debug:msg: "I am handler1"- name: handler2debug:msg: "I am handler2"
运行结果如下：
TASK [task1] ***************************************************************************************
ok: [192.168.1.55] => {"msg": "I am task1"
}TASK [task2] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task2"
}TASK [task3] ***************************************************************************************
ok: [192.168.1.55] => {"msg": "I am task3"
}RUNNING HANDLER [handler1] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler1"
}RUNNING HANDLER [handler2] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler2"
}
可见：
- 一个task可以nofiy多个handler
- 多个handler的运行顺序和notify时的顺序无关，只和handler本身的顺序有关（本例中，notify的顺序是handler2在handler1之前，但运行时是按handler本身的顺序，handler1在handler2之前）
- handler在所有task运行结束之后才运行（本例中，task2 notify了handler，但handler是在task3之后才运行的）
---
- hosts: alltasks:- name: task1debug:msg: "I am task1"changed_when: truenotify:- handler1- name: task2debug:msg: "I am task2"changed_when: truenotify:- handler1handlers:- name: handler1debug:msg: "I am handler1"
运行结果如下：
TASK [task1] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task1"
}TASK [task2] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task2"
}RUNNING HANDLER [handler1] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler1"
}
可见，若多个task notify同一个handler，该handler只会运行一次。
通过 listen 匹配topic
前面的例子，在notify时，是通过handler的 name 来匹配topic的。也可以通过handler的 listen 来匹配：
---
- hosts: alltasks:- name: task1debug:msg: "I am task1"changed_when: truenotify:- task1 changed- name: task2debug:msg: "I am task2"changed_when: truenotify:- task2 changedhandlers:- name: handler1debug:msg: "I am handler1"listen:- "task2 changed"- "task1 changed"
运行结果如下：
TASK [task1] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task1"
}TASK [task2] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task2"
}RUNNING HANDLER [handler1] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler1"
}
可见，通过 listen ，一个handler可以监听多个nofiy的topic。
考一考
下面的play，运行结果是什么？
---
- hosts: alltasks:- name: task1debug:msg: "I am task1"changed_when: truenotify:- task1 changed- name: task2debug:msg: "I am task2"changed_when: truenotify:- task2 changedhandlers:- name: handler1debug:msg: "I am handler1"listen: "task2 changed"- name: handler2debug:msg: "I am handler2"listen:- "task2 changed"- "task1 changed"- name: handler3debug:msg: "I am handler3"listen: "task1 changed"
答：运行结果为：
TASK [task1] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task1"
}TASK [task2] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task2"
}RUNNING HANDLER [handler1] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler1"
}RUNNING HANDLER [handler2] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler2"
}RUNNING HANDLER [handler3] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler3"
}
立即运行handler
前面提到，handler是在所有task运行结束后才运行的。如果想要立即运行handler，可用 meta: flush_handlers ：
---
- hosts: alltasks:- name: task1debug:msg: "I am task1"changed_when: truenotify: handler2- name: flushmeta: flush_handlers- name: task2debug:msg: "I am task2"changed_when: truenotify: handler1- name: task3debug:msg: "I am task3"handlers:- name: handler1debug:msg: "I am handler1"- name: handler2debug:msg: "I am handler2"
运行结果如下：
TASK [task1] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task1"
}TASK [flush] ***************************************************************************************RUNNING HANDLER [handler2] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler2"
}TASK [task2] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task2"
}TASK [task3] ***************************************************************************************
ok: [192.168.1.55] => {"msg": "I am task3"
}RUNNING HANDLER [handler1] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler1"
}
可见，flush之后，handler2立即运行了，而handler1则是在所有task都运行结束之后才运行的。
注意：flush触发运行的handler，如果随后又被notify，还会再次运行：
---
- hosts: alltasks:- name: task1debug:msg: "I am task1"changed_when: truenotify: handler1- name: flushmeta: flush_handlers- name: task2debug:msg: "I am task2"changed_when: truenotify: handler1handlers:- name: handler1debug:msg: "I am handler1"
运行结果如下：
TASK [task1] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task1"
}TASK [flush] ***************************************************************************************RUNNING HANDLER [handler1] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler1"
}TASK [task2] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task2"
}RUNNING HANDLER [handler1] *************************************************************************
ok: [192.168.1.55] => {"msg": "I am handler1"
}
可见，handler1运行了两次。
handler的命名最好不要包含变量
---
- hosts: allvars:var1: "aaa"tasks:- name: task1debug:msg: "I am task1"changed_when: truenotify: handler {{ var1 }}handlers:- name: handler {{ var1 }}debug:msg: "I am handler1"
运行结果如下：
TASK [task1] ***************************************************************************************
changed: [192.168.1.55] => {"msg": "I am task1"
}RUNNING HANDLER [handler aaa] **********************************************************************
ok: [192.168.1.55] => {"msg": "I am handler1"
}
没有问题。但是，这里有个潜在的问题：
---
- hosts: all#vars:# var1: "aaa"tasks:- name: task0set_fact:var1: "aa"- name: task1debug:msg: "I am task1"changed_when: truenotify: handler {{ var1 }} # 可以识别handlers:- name: handler {{ var1 }} # 无法识别debug:msg: "I am handler1"
运行结果如下：
TASK [task0] ***************************************************************************************
ok: [192.168.1.55]TASK [task1] ***************************************************************************************
[WARNING]: Handler 'handler {{ var1 }}' is unusable because it has no listen topics and the name
could not be templated (host-specific variables are not supported in handler names). The error:
'var1' is undefined. 'var1' is undefined
ERROR! The requested handler 'handler aa' was not found in either the main handlers list nor in the listening handlers list
可见，对于动态定义的变量，notify可以识别，而handler命名处无法识别（未定义）。
类似的，如果已定义的变量，如果动态改变其值，notify可以识别，而handler命名处仍然是原值。
所以，最好不要在handler命名处使用变量。
参考
https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_handlers.html
：频域筛选机制增强细节感知，优化复杂场景目标检测)
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