Block-rescue-always

1. Playbooks 中的區塊 (block) 經常配合 when 條件在某些狀況下執行，本章介紹當 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:
       - ansible.builtin.debug:
           msg: 'I execute normally'
       - name: i force a failure
         command: /bin/false
       - ansible.builtin.debug:
           msg: 'I never execute, due to the above task failing, :-('
     rescue:
       - ansible.builtin.debug:
           msg: 'I caught an error'
       - name: i force a failure in middle of recovery! >:-)
         command: /bin/false
       - ansible.builtin.debug:
           msg: 'I also never execute :-('
     always:
       - ansible.builtin.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。

   ceuser@deyu:~/ansible_pb$ ansible-doc debug | grep ^EX -A4
   EXAMPLES:
   
   - name: Print the gateway for each host when defined
     ansible.builtin.debug:
       msg: System {{ inventory_hostname }} has gateway {{ ansible_default_ipv4.gateway }}