由于Ansible幂等性的特性，有时前一个task发生了变化，后续的task无变化并不会重新执行，

但后续的task却可能受前一个task变化而影响。使用hanlder和notify即可解决此问题，handler

用于当关注的资源发生变化时，才会采取一定的操作。在notify中列出的操作称为handler，

也即notify中调用handler中定义的操作

示例：

vim http.yml

—

– host: websrvs

remote_user: root

tasks:

– name: install httpd package

yum: name=httpd

– name: copy conf file

copy: src=files/httpd.conf dest=/etc/httpd/conf/ backup=yes

– name: start service

service: name=httpd state=startd enable=yes

vim /files/httpd.conf

Listen 8080

ansible-playbook http.yml

此时无法重启服务，端口仍为80

vim http.yml

—

– host: websrvs

remote_user: root

tasks:

– name: install httpd package

yum: name=httpd

– name: copy conf file

copy: src=files/httpd.conf dest=/etc/httpd/conf/ backup=yes

notify: restart service

– name: start service

service: name=httpd state=startd enable=yes

handlers:

– name: restart service

service: name=httpd state=restarted

由于httpd.conf发生了变化，触发了notify，执行相应的handler操作，httpd服务重启后

监听端口变为8080