Block-rescue-always

1. 前面章節 Playbooks 介紹過區塊 (block)，經常配合 when 修件在某些狀況下執行，當 block 執行任務出現錯誤時，執行 rescue 任務，而 always 則不管有無錯誤都執行。

   - name: Attempt and graceful roll back demo
     block:
       - debug:
           msg: 'I execute normally'
       - name: i force a failure
         command: /bin/false
       - debug:
           msg: 'I never execute, due to the above task failing, :-('
     rescue:
       - debug:
           msg: 'I caught an error'
       - name: i force a failure in middle of recovery! >:-)
         command: /bin/false
       - debug:
           msg: 'I also never execute :-('
     always:
       - debug:
           msg: "This always executes"
   

2. debug 模組的 msg 列印客製化訊息，如果省略則預設列印 "Hello World!"，查看 debug 模組範例。

   [deyu1@kvm19 ansible]$ ansible-doc debug | grep ^EX -A4
   EXAMPLES:
   
   # Example that prints the loopback address and gateway for each host
   - debug:
       msg: System {{ inventory_hostname }} has uuid {{ ansible_product_uuid }}