介绍：block是ansible在2.0版本引入的一个特性，块功能可以将任务进行逻辑分组，并且可以在块级别上应用任务变量。同时也可以使用类似于其他编程语言处理异常那样的方法，来处理块内部的任务异常。

     原理：block中的组任务，都会继承block的属相（支持when，不支持with_items），部署时会分别执行组中的任务，并且都会继承block的属相（在任务后添加block的when条件）

1、常规使用

--- - hosts: localhost   tasks:        - block:         - yum: name={{ item }} state=installed           with_items:              - httpd              - memcached         - template: src=templates/src.j2 dest=/etc/foo.conf         - name： start service           service: name=bar state=started enabled=True       when: ansible_distribution == 'CentOS'       become: true       become_user: root

2、异常处理

rescue：只有脚本报错时才执行

always：无论结果如何都执行

--- - hosts: localhost    tasks:    - block:        - debug: msg='I execute normally'        - command: /bin/false        - debug: msg='I never execute, due to the above task failing'      rescue:        - debug: msg='I caught an error'        - command: /bin/false        - debug: msg='I also never execute :-('      always:        - debug: msg="this always executes"

      The tasks in the block would execute normally, if there is any error the rescue section would get executed with whatever you need to do to recover from the previous error. The always section runs no matter what previous error did or did not occur in the block and rescue sections.

3、常见陷阱

（1）在2.0中添加了块特性，在2.3中添加了块的name特性

错误反例(2.3以下不支持。2.3及以上就支持了)

--- - hosts: localhost   tasks:     - name: bbbb          #2.3以下的正确姿势应该去掉block的name       block:           - name: bbbb           shell: echo bbbb       when: false      - name: cccc       shell: echo cccc  #-----报错  - name: bbbb       ^ here

（2）block中不能添加注册的变量

原因：如果block的when结果是false，就不会执行任务获得注册变量的值，但是组中有些任务调用此注册变量，就会任务失败。

--- - hosts: localhost   tasks:     - block:         - name: aaaa           shell: echo aaaa         - name: bbbb           shell: echo bbbb           register: results               #-------后面调用会导致失败         - name: echo {{results.stdout}}   #-------调用了，此任务会失败           shell: echo cccc       when: false      - name: dddd       shell: echo dddd

 解决办法：可以给block的vars属相添加变量，在block的组任务中进行调用

--- - hosts: localhost   tasks:     - name: bbbb       shell: echo bbb       register: result                    #-------注册result变量     - block:         - name: aaaa           shell: echo aaaa         - name: echo {{results}}          #-------调用了           shell: echo cccc       when: false       vars:         results: "{{result.stdout}}"      #-------使用vars，将注册的result放入block中results变量中      - name: dddd       shell: echo dddd 

（3）block没有with_items属相

--- - hosts: localhost   tasks:     - block:         - name: aaaa           shell: echo aaaa       with_items:                #-----会报错，block不支持此属相         - myname: dxx                 when: false      - name: dddd       shell: echo dddd