import_tasks和include_tasks比较

概括起来讲，import_tasks 是静态的，include_tasks 是动态的。静态和动态的区别集中在被 include 文件的加载时机不同。
静态的意思是被 include 的文件在 playbook 被加载时就展开了，在预处理阶段。
动态的意思是被 include 的文件在 playbook 运行时展开。

以下通过示例直观表述：
1.

[root@yangzhen ansibletest]# less playbooks/test8.yml 
---
- hosts: localhost
  gather_facts: no

  vars:
    filename: test.yml

  tasks:
    - import_tasks: "{{ filename }}"
    - include_tasks: "{{ filename }}"
[root@yangzhen ansibletest]# less playbooks/test.yml 
---
- name: Used to check difference between import_tasks and include_tasks
  debug:
    msg: "Test import_tasks and include_tasks"
[root@yangzhen ansibletest]# ansible-playbook playbooks/test8.yml 

PLAY [localhost] *****************************************************************************************************************************************************

TASK [Used to check difference between import_tasks and include_tasks] ***********************************************************************************************
ok: [localhost] => {
    "msg": "Test import_tasks and include_tasks"
}

TASK [include_tasks] *************************************************************************************************************************************************
included: /root/yz/ansibletest/playbooks/test.yml for localhost

TASK [Used to check difference between import_tasks and include_tasks] ***********************************************************************************************
ok: [localhost] => {
    "msg": "Test import_tasks and include_tasks"
}

PLAY RECAP ***********************************************************************************************************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0   

2. 将 test8.yml 中 vars 定义变量，改为 set_fact 方式

[root@yangzhen ansibletest]# less playbooks/test8.yml 
---
- hosts: localhost
  gather_facts: no

  #vars:
  #  filename: test.yml

  tasks:
    - set_fact:
        filename: test.yml
    - import_tasks: "{{ filename }}"
    - include_tasks: "{{ filename }}"

再次运行：

[root@yangzhen ansibletest]# ansible-playbook playbooks/test8.yml
ERROR! Error when evaluating variable in include name: {{ filename }}.

When using static includes, ensure that any variables used in their names are defined in vars/vars_files
or extra-vars passed in from the command line. Static includes cannot use variables from inventory
sources like group or host vars.

上述的意思是，在使用 import_tasks 引用变量时，要确保变量定义在 vars/vars_file或命令行中。如使用 var_files定义变量直观观察下。
将test8.yml修改如下

---
- hosts: localhost
  gather_facts: no

  vars_files:
    - variable.yml

  tasks:
    - import_tasks: "{{ filename }}"
    - include_tasks: "{{ filename }}"
[root@yangzhen ansibletest]# cat playbooks/variable.yml 
---
filename: test.yml

执行

[root@yangzhen ansibletest]# ansible-playbook playbooks/test8.yml 

PLAY [localhost] *****************************************************************************************************************************************************

TASK [Used to check difference between import_tasks and include_tasks] ***********************************************************************************************
ok: [localhost] => {
    "msg": "Test import_tasks and include_tasks"
}

TASK [include_tasks] *************************************************************************************************************************************************
included: /root/yz/ansibletest/playbooks/test.yml for localhost

TASK [Used to check difference between import_tasks and include_tasks] ***********************************************************************************************
ok: [localhost] => {
    "msg": "Test import_tasks and include_tasks"
}

PLAY RECAP ***********************************************************************************************************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0   

总结：import_tasks 直接引用的变量，要定义在vars/vars_file或命令行。
2. when 关键字对 include_tasks 和 import_tasks 有着本质区别
当对 import_tasks 使用 when 进行条件判断时，when 对应的条件会被应用于 include 文件中的每一个任务，意思是每要执行一个任务时，都要先进行条件判断。总结起来就是顺序执行 include 文件中列出的每一个任务前，都要进行条件判断，满足条件就执行，不满足就跳过，需要多次判断。
当对 include_tasks 使用 when 进行条件判断时，when 对应的条件只应用一次，发生在是否include这个文件，若include，则执行这个include文件中所有的任务，不再进行其他判断。
通过示例直观分析

[root@yangzhen ansibletest]# less playbooks/test9.yml 
---
- hosts: localhost
  gather_facts: no

  tasks:
    - name: 'set variable to 0'
      set_fact:
        testnum: 0
    - debug:
        msg: 'enter the include file test10.yml'
    - include_tasks: test10.yml
      when: testnum == 0

   - name: 'set variable to 0'
     set_fact:
       testnum: 0
   - debug:
       msg: 'enter the include file test10.yml'
   - import_tasks: test10.yml
     when: testnum == 0
[root@yangzhen ansibletest]# less playbooks/test10.yml
---
- set_fact:
    testnum: 1

- debug:
    msg: 'exective in test10.yml'

[root@yangzhen ansibletest]# ansible-playbook playbooks/test9.yml 

PLAY [localhost] *****************************************************************************************************************************************************

TASK [set variable to 0] *********************************************************************************************************************************************
ok: [localhost]

TASK [debug] *********************************************************************************************************************************************************
ok: [localhost] => {
    "msg": "enter the include file test10.yml"
}

TASK [include_tasks] *************************************************************************************************************************************************
included: /root/yz/ansibletest/playbooks/test10.yml for localhost

TASK [set_fact] ******************************************************************************************************************************************************
ok: [localhost]

TASK [debug] *********************************************************************************************************************************************************
ok: [localhost] => {
    "msg": "exective in test10.yml"
}

TASK [set variable to 0] *********************************************************************************************************************************************
ok: [localhost]

TASK [debug] *********************************************************************************************************************************************************
ok: [localhost] => {
    "msg": "enter the include file test10.yml"
}

TASK [set_fact] ******************************************************************************************************************************************************
ok: [localhost]

TASK [debug] *********************************************************************************************************************************************************
skipping: [localhost]

PLAY RECAP ***********************************************************************************************************************************************************
localhost                  : ok=8    changed=0    unreachable=0    failed=0   

调试信息"enter the include file test10.yml"只输出了一次，发生在 include_tasks 阶段。之后将变量 testnum 重新设置为 0，条件满足时，include test10.yml, 进入 test10.yml 文件执行，在其中将 testnum 设置为 1，然后执下一条任务，进行条件判断，此时 testnum 不为0，所以不满足条件，跳过该任务。

3. 使用 loop 或 with_items 关键字对 include 文件进行循环操作时，只能配合 include_tasks。