ansible loop循环

1. 概述

• ansible循环官方文档 Loops
• ansible提供loop、with_<lookup>、until等关键字来多次执行任务。
• ansible在2.5版本中引入了loop循环，它尚未完全替代 with_<lookup>，但ansible官方建议在大多数用例中使用它。
• ansible并没有废弃with_<lookup>,目前认为该语法仍然是有效的。

2. loop与with_的区别

The with_lookup keywords rely on Lookup plugins - even items is a lookup.

The loop keyword is equivalent to with_list, and is the best choice for simple loops.

The loop keyword will not accept a string as input, see Ensuring list input for loop: using query rather than lookup.

Generally speaking, any use of with_* covered in Migrating from with_X to loop can be updated to use loop.

Be careful when changing with_items to loop, as with_items performed implicit single-level flattening. You may need to use flatten(1) with loop to match the exact outcome.

即：

• with_*依赖lookup插件，items也是一个lookup插件。
• loop关键字与with_list等价，对于简单循环，使用loop是最好的选择。
• loop关键字不接受字符串输入。
• 通常来说，使用with_*关键字时，也可以使用loop进行代替。
• 当从with_items转换成loop时，需要特别小心。你需要使用flatten(1)对列表进行展平。

2.1 列表展平

• flatten过滤器请参考 ansible.builtin.flatten filter – flatten lists within a list 。

  For example, to get the same output as:

with_items:
  - 1
  - [2,3]
  - 4

转换成loop时，需要这样：

loop: "{{ [1, [2, 3], 4] | flatten(1) }}"

我们来编写loop.yml剧本文件，来测试一下：

- hosts: node1
  tasks:
    - name: use with_items
      ansible.builtin.debug:
        msg: "The number is: {{ item }}"
      with_items:
        - 1
        - [2,3]
        - 4

    - name: use loop with flatten
      ansible.builtin.debug:
        msg: "The number is: {{ item }}"
      loop: "{{ [1, [2, 3], 4] | flatten(1) }}"

    - name: use loop without flatten
      ansible.builtin.debug:
        msg: "The number is: {{ item }}"
      loop: "{{ [1, [2, 3], 4] }}"

检查剧本并运行：

[ansible@master ansible_playbooks]$ ansible-lint loop.yml
[ansible@master ansible_playbooks]$ ansible-playbook loop.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ***********************************************************************************************************

TASK [Gathering Facts] *************************************************************************************************
ok: [node1]

TASK [use with_items] **************************************************************************************************
ok: [node1] => (item=1) => {
    "msg": "The number is: 1"
}
ok: [node1] => (item=2) => {
    "msg": "The number is: 2"
}
ok: [node1] => (item=3) => {
    "msg": "The number is: 3"
}
ok: [node1] => (item=4) => {
    "msg": "The number is: 4"
}

TASK [use loop with flatten] *******************************************************************************************
ok: [node1] => (item=1) => {
    "msg": "The number is: 1"
}
ok: [node1] => (item=2) => {
    "msg": "The number is: 2"
}
ok: [node1] => (item=3) => {
    "msg": "The number is: 3"
}
ok: [node1] => (item=4) => {
    "msg": "The number is: 4"
}

TASK [use loop without flatten] ****************************************************************************************
ok: [node1] => (item=1) => {
    "msg": "The number is: 1"
}
ok: [node1] => (item=[2, 3]) => {
    "msg": "The number is: [2, 3]"
}
ok: [node1] => (item=4) => {
    "msg": "The number is: 4"
}

PLAY RECAP *************************************************************************************************************
node1                      : ok=4    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

运行效果图：

可以看到，with_items默认会将列表的的元素展平1层，子元素[2,3]被展平后，当作两个元素2和3被打印了出来，此时与使用

loop: "{{ [1, [2, 3], 4] | flatten(1) }}"

等价。当loop中没有使用flatten过滤器时，子元素被原样打印出来，子元素[2,3]被当作一个元素输出了。

为了更深入研究两者的不同，我们修改一下剧本文件内容：

- hosts: node1
  tasks:
    - name: use with_items
      ansible.builtin.debug:
        msg: "The number is: {{ item }}"
      with_items:
        - 1
        - [2,3]
        - 4
        - [[5,6],[7,8]]

    - name: use loop with flatten one level
      ansible.builtin.debug:
        msg: "The number is: {{ item }}"
      loop: "{{ [1, [2, 3], 4, [[5,6],[7,8]]] | flatten(1) }}"

    - name: use loop with flatten two level
      ansible.builtin.debug:
        msg: "The number is: {{ item }}"
      loop: "{{ [1, [2, 3], 4, [[5,6],[7,8]]] | flatten(2) }}"

    - name: use loop flatten
      ansible.builtin.debug:
        msg: "The number is: {{ item }}"
      loop: "{{ [1, [2, 3], 4, [[5,6],[7,8]]]|flatten }}"

在最后增加了元素[[5,6],[7,8]]，然后再次运行剧本：

[ansible@master ansible_playbooks]$ ansible-lint loop.yml
[ansible@master ansible_playbooks]$ ansible-playbook loop.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ****************************************************************************************************************

TASK [Gathering Facts] ******************************************************************************************************
ok: [node1]

TASK [use with_items] *******************************************************************************************************
ok: [node1] => (item=1) => {
    "msg": "The number is: 1"
}
ok: [node1] => (item=2) => {
    "msg": "The number is: 2"
}
ok: [node1] => (item=3) => {
    "msg": "The number is: 3"
}
ok: [node1] => (item=4) => {
    "msg": "The number is: 4"
}
ok: [node1] => (item=[5, 6]) => {
    "msg": "The number is: [5, 6]"
}
ok: [node1] => (item=[7, 8]) => {
    "msg": "The number is: [7, 8]"
}

TASK [use loop with flatten one level] **************************************************************************************
ok: [node1] => (item=1) => {
    "msg": "The number is: 1"
}
ok: [node1] => (item=2) => {
    "msg": "The number is: 2"
}
ok: [node1] => (item=3) => {
    "msg": "The number is: 3"
}
ok: [node1] => (item=4) => {
    "msg": "The number is: 4"
}
ok: [node1] => (item=[5, 6]) => {
    "msg": "The number is: [5, 6]"
}
ok: [node1] => (item=[7, 8]) => {
    "msg": "The number is: [7, 8]"
}

TASK [use loop with flatten two level] **************************************************************************************
ok: [node1] => (item=1) => {
    "msg": "The number is: 1"
}
ok: [node1] => (item=2) => {
    "msg": "The number is: 2"
}
ok: [node1] => (item=3) => {
    "msg": "The number is: 3"
}
ok: [node1] => (item=4) => {
    "msg": "The number is: 4"
}
ok: [node1] => (item=5) => {
    "msg": "The number is: 5"
}
ok: [node1] => (item=6) => {
    "msg": "The number is: 6"
}
ok: [node1] => (item=7) => {
    "msg": "The number is: 7"
}
ok: [node1] => (item=8) => {
    "msg": "The number is: 8"
}

TASK [use loop flatten] *********************************************************************************************
ok: [node1] => (item=1) => {
    "msg": "The number is: 1"
}
ok: [node1] => (item=2) => {
    "msg": "The number is: 2"
}
ok: [node1] => (item=3) => {
    "msg": "The number is: 3"
}
ok: [node1] => (item=4) => {
    "msg": "The number is: 4"
}
ok: [node1] => (item=5) => {
    "msg": "The number is: 5"
}
ok: [node1] => (item=6) => {
    "msg": "The number is: 6"
}
ok: [node1] => (item=7) => {
    "msg": "The number is: 7"
}
ok: [node1] => (item=8) => {
    "msg": "The number is: 8"
}

PLAY RECAP ******************************************************************************************************************
node1                      : ok=5    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

可以看到,with_items只会展平一层，[[5,6],[7,8]]展平后输出[5,6],[7,8]两个元素，但不会被再次展平。而:

loop: "{{ [1, [2, 3], 4, [[5,6],[7,8]]] | flatten(2) }}"

会展平2层，所有数字单独输出了。而:

loop: "{{ [1, [2, 3], 4, [[5,6],[7,8]]]|flatten }}"

不指定层数时，则将所有子元素全部展平。

2.2 loop不一定比with_方便

• 任何需要在loop中使用lookup的with_*语句都不应转换为使用loop循环关键字。例如，不要执行以下操作：

loop: "{{ lookup('fileglob', '*.txt', wantlist=True) }}"

应直接使用以下表达式更简洁：

with_fileglob: '*.txt'

此时可以看到，使用with_fileglob语法更简洁明了！

3. 标准循环

3.1 简单循环

执行重启任务时，你可以直接在任务中通过将字符串组成的列表写成一个标准循环：

- name: Add several users
  ansible.builtin.user:
    name: "{{ item }}"
    state: present
    groups: "wheel"
  loop:
     - testuser1
     - testuser2

以上示例，会创建testuser1和testuser2两个用户。

你也可以提前定义一个列表变量，或者写到vars块中，然后就可以像下面这样引用列表变量了：

loop: "{{ somelist }}"

达到的效果，与下面这种创建两个任务的剧本效果是一样的：

- name: Add user testuser1
  ansible.builtin.user:
    name: "testuser1"
    state: present
    groups: "wheel"

- name: Add user testuser2
  ansible.builtin.user:
    name: "testuser2"
    state: present
    groups: "wheel"

但我们通过循环就可以少写一个任务。

有的插件支持接受列表作为一个参数，像yum、apt包管理工具，支持列表参数，这时比使用loop循环更好。

如下示例：

- name: Optimal yum
  ansible.builtin.yum:
    name: "{{ list_of_packages }}"
    state: present

- name: Non-optimal yum, slower and may cause issues with interdependencies
  ansible.builtin.yum:
    name: "{{ item }}"
    state: present
  loop: "{{ list_of_packages }}"

此时使用loop循环时，可能会出现依赖性问题，安装变得更慢等。

3.2 迭代列表子项

如果您有哈希列表，则可以在循环中引用子项。如：

- name: Add several users
  ansible.builtin.user:
    name: "{{ item.name }}"
    state: present
    groups: "{{ item.groups }}"
  loop:
    - { name: 'testuser1', groups: 'wheel' }
    - { name: 'testuser2', groups: 'root' }

可以看到，通过item.name或item.groups就可以访问列表子项的name和groups属性了。

将条件与循环组合时，when:语句会针对每个项目单独处理，详细可参考Using conditionals in loops

此处摘取一个示例：

tasks:
    - name: Run with items greater than 5
      ansible.builtin.command: echo {{ item }}
      loop: [ 0, 2, 4, 6, 8, 10 ]
      when: item > 5

此示例只会输出列表中大于5的元素。

编写剧本文件with_loop.yml：

- hosts: node1
  tasks:
    - name: Run with items greater than 5
      ansible.builtin.command: echo {{ item }}
      loop: [ 0, 2, 4, 6, 8, 10 ]
      when: item > 5

运行剧本：

[ansible@master ansible_playbooks]$ ansible-playbook with_loop.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ***********************************************************************************************************

TASK [Gathering Facts] *************************************************************************************************
ok: [node1]

TASK [Run with items greater than 5] ***********************************************************************************
skipping: [node1] => (item=0)  => {"ansible_loop_var": "item", "changed": false, "item": 0, "skip_reason": "Conditional result was False"}
skipping: [node1] => (item=2)  => {"ansible_loop_var": "item", "changed": false, "item": 2, "skip_reason": "Conditional result was False"}
skipping: [node1] => (item=4)  => {"ansible_loop_var": "item", "changed": false, "item": 4, "skip_reason": "Conditional result was False"}
changed: [node1] => (item=6) => {"ansible_loop_var": "item", "changed": true, "cmd": ["echo", "6"], "delta": "0:00:00.011140", "end": "2023-09-03 13:30:34.422449", "item": 6, "rc": 0, "start": "2023-09-03 13:30:34.411309", "stderr": "", "stderr_lines": [], "stdout": "6", "stdout_lines": ["6"]}
changed: [node1] => (item=8) => {"ansible_loop_var": "item", "changed": true, "cmd": ["echo", "8"], "delta": "0:00:00.011377", "end": "2023-09-03 13:30:34.679076", "item": 8, "rc": 0, "start": "2023-09-03 13:30:34.667699", "stderr": "", "stderr_lines": [], "stdout": "8", "stdout_lines": ["8"]}
changed: [node1] => (item=10) => {"ansible_loop_var": "item", "changed": true, "cmd": ["echo", "10"], "delta": "0:00:00.013275", "end": "2023-09-03 13:30:34.933122", "item": 10, "rc": 0, "start": "2023-09-03 13:30:34.919847", "stderr": "", "stderr_lines": [], "stdout": "10", "stdout_lines": ["10"]}

PLAY RECAP *************************************************************************************************************
node1                      : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

可以看到，当item=0/2/4时，没有执行echo语句，因为其不满足条件item>5,所以被忽略了。

3.3 迭代字典

要迭代一个字典，请使用dict2items过滤器：

- name: Using dict2items
  ansible.builtin.debug:
    msg: "{{ item.key }} - {{ item.value }}"
  loop: "{{ tag_data | dict2items }}"
  vars:
    tag_data:
      Environment: dev
      Application: payment

示例打印出一字典的键和键值。

编写剧本文件loop_dict.yml:

- hosts: node1
  tasks:
    - name: Using dict2items
      ansible.builtin.debug:
        msg: "{{ item.key }} - {{ item.value }}"
      loop: "{{ tag_data | dict2items }}"
      vars:
        tag_data:
          Environment: dev
          Application: payment

运行效果：

[ansible@master ansible_playbooks]$ ansible-lint loop_dict.yml
[ansible@master ansible_playbooks]$ ansible-playbook loop_dict.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ***********************************************************************************************************

TASK [Gathering Facts] *************************************************************************************************
ok: [node1]

TASK [Using dict2items] ************************************************************************************************
ok: [node1] => (item={u'key': u'Environment', u'value': u'dev'}) => {
    "msg": "Environment - dev"
}
ok: [node1] => (item={u'key': u'Application', u'value': u'payment'}) => {
    "msg": "Application - payment"
}

PLAY RECAP *************************************************************************************************************
node1                      : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

4. 在循环中注册变量

可以将循环的输出注册到变量中，请看以下示例。

编写剧本文件loop_register.yml：

- hosts: node1
  tasks:
    - name: Register loop output as a variable
      ansible.builtin.shell: "echo {{ item }}"
      loop:
        - "one"
        - "two"
      register: ECHO

    - name: print variable ECHO
      ansible.builtin.debug:
        msg: "The ECHO value is: {{ ECHO }}"

检查并运行剧本：

[ansible@master ansible_playbooks]$ ansible-lint loop_register.yml
[ansible@master ansible_playbooks]$ ansible-playbook loop_register.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ***********************************************************************************************************

TASK [Gathering Facts] *************************************************************************************************
ok: [node1]

TASK [Register loop output as a variable] ******************************************************************************
changed: [node1] => (item=one) => {"ansible_loop_var": "item", "changed": true, "cmd": "echo one", "delta": "0:00:00.012806", "end": "2023-09-03 22:35:44.884414", "item": "one", "rc": 0, "start": "2023-09-03 22:35:44.871608", "stderr": "", "stderr_lines": [], "stdout": "one", "stdout_lines": ["one"]}
changed: [node1] => (item=two) => {"ansible_loop_var": "item", "changed": true, "cmd": "echo two", "delta": "0:00:00.013549", "end": "2023-09-03 22:35:45.152964", "item": "two", "rc": 0, "start": "2023-09-03 22:35:45.139415", "stderr": "", "stderr_lines": [], "stdout": "two", "stdout_lines": ["two"]}

TASK [print variable ECHO] *********************************************************************************************
ok: [node1] => {
    "msg": "The ECHO value is: {'msg': u'All items completed', 'changed': True, 'results': [{'stderr_lines': [], 'ansible_loop_var': u'item', u'end': u'2023-09-03 22:35:44.884414', 'failed': False, u'stdout': u'one', u'changed': True, u'rc': 0, 'item': u'one', u'cmd': u'echo one', u'stderr': u'', u'delta': u'0:00:00.012806', u'invocation': {u'module_args': {u'creates': None, u'executable': None, u'_uses_shell': True, u'strip_empty_ends': True, u'_raw_params': u'echo one', u'removes': None, u'argv': None, u'warn': True, u'chdir': None, u'stdin_add_newline': True, u'stdin': None}}, 'stdout_lines': [u'one'], u'start': u'2023-09-03 22:35:44.871608'}, {'stderr_lines': [], 'ansible_loop_var': u'item', u'end': u'2023-09-03 22:35:45.152964', 'failed': False, u'stdout': u'two', u'changed': True, u'rc': 0, 'item': u'two', u'cmd': u'echo two', u'stderr': u'', u'delta': u'0:00:00.013549', u'invocation': {u'module_args': {u'creates': None, u'executable': None, u'_uses_shell': True, u'strip_empty_ends': True, u'_raw_params': u'echo two', u'removes': None, u'argv': None, u'warn': True, u'chdir': None, u'stdin_add_newline': True, u'stdin': None}}, 'stdout_lines': [u'two'], u'start': u'2023-09-03 22:35:45.139415'}]}"
}

PLAY RECAP *************************************************************************************************************
node1                      : ok=3    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

当您使用带有循环的register注册变量时，放置在变量中的数据结构将包含一个结果属性，该属性是来自模块的所有响应的列表。 这与使用不带循环的寄存器时返回的数据结构不同。

复杂的循环请参考官方文档。

5. 循环主机清单

如果你要对主机清单（Inventory）进行循环，或者对其子集进行循环，你可以使用loop和ansible_play_batch或groups变量来进行循环处理：

编写剧本文件loop_inventory.yml：

- hosts: all
  tasks:
    - name: Show all the hosts in the inventory
      ansible.builtin.debug:
        msg: "{{ item }}"
      loop: "{{ groups['all'] }}"

    - name: Show all the hosts in the current play
      ansible.builtin.debug:
        msg: "{{ item }}"
      loop: "{{ ansible_play_batch }}"

检查并运行：

[ansible@master ansible_playbooks]$ ansible-lint loop_inventory.yml
[ansible@master ansible_playbooks]$ ansible-playbook loop_inventory.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [all] *************************************************************************************************************

TASK [Gathering Facts] *************************************************************************************************
ok: [node1]

TASK [Show all the hosts in the inventory] *****************************************************************************
ok: [node1] => (item=node1) => {
    "msg": "node1"
}

TASK [Show all the hosts in the current play] **************************************************************************
ok: [node1] => (item=node1) => {
    "msg": "node1"
}

PLAY RECAP *************************************************************************************************************
node1                      : ok=3    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

由于我测试的时候只有一个节点node1，所以就算hosts；all指定是所有主机，显示也是只有node1一台主机。但可以看到通过groups['all']或ansible_play_batch变量输出的结果是一样的。

Ansible中的特殊变量，可以参考: Special Variables

6. 循环控制

• 可以通过loop_control关键字对循环进行控制，如控制item标签名称、循环暂停、索引变量等。

6.1 设置标签名称

When looping over complex data structures, the console output of your task can be enormous.

即当循环复杂的数据结构时，任务的控制台输出可能会很大，不便于阅读。通过设置标签名称，可以使控制台输出更易读。

我们参考官方示例写一个循环剧本loop_lebel.yml:

- hosts: node1
  tasks:
    - name: Show servers info
      ansible.builtin.debug:
        msg: "The server name is: {{ item }}"
      loop:
        - name: server1
          disks: 3gb
          ram: 15Gb
          network:
            nic01: 100Gb
            nic02: 10Gb

        - name: server2
          disks: 3gb
          ram: 15Gb
          network:
            nic01: 100Gb
            nic02: 10Gb

剧本中对两个服务器信息进行循环处理。

检查并运行剧本：

[ansible@master ansible_playbooks]$ ansible-lint loop_label.yml
[ansible@master ansible_playbooks]$ ansible-playbook loop_label.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ***********************************************************************************************************

TASK [Gathering Facts] *************************************************************************************************
ok: [node1]

TASK [Show servers info] ***********************************************************************************************
ok: [node1] => (item={u'disks': u'3gb', u'ram': u'15Gb', u'name': u'server1', u'network': {u'nic02': u'10Gb', u'nic01': u'100Gb'}}) => {
    "msg": "The server name is: {u'disks': u'3gb', u'ram': u'15Gb', u'name': u'server1', u'network': {u'nic02': u'10Gb', u'nic01': u'100Gb'}}"
}
ok: [node1] => (item={u'disks': u'3gb', u'ram': u'15Gb', u'name': u'server2', u'network': {u'nic02': u'10Gb', u'nic01': u'100Gb'}}) => {
    "msg": "The server name is: {u'disks': u'3gb', u'ram': u'15Gb', u'name': u'server2', u'network': {u'nic02': u'10Gb', u'nic01': u'100Gb'}}"
}

PLAY RECAP *************************************************************************************************************
node1                      : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

可以看到，此时item对应的标签信息就是循环对象的值，直接输出了服务器字典信息。

下面来设置标签：

- hosts: node1
  tasks:
    - name: Show servers info
      ansible.builtin.debug:
        msg: "The server name is: {{ item }}"
      loop:
        - name: server1
          disks: 3gb
          ram: 15Gb
          network:
            nic01: 100Gb
            nic02: 10Gb

        - name: server2
          disks: 3gb
          ram: 15Gb
          network:
            nic01: 100Gb
            nic02: 10Gb
      loop_control:
        label: "{{ item.name }}"

此时，通过loop_control控制，增加标签:

label: "{{ item.name }}"

此时运行剧本：

[ansible@master ansible_playbooks]$ ansible-playbook loop_label.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ************************************************************************************************************

TASK [Gathering Facts] **************************************************************************************************
ok: [node1]

TASK [Show servers info] ************************************************************************************************
ok: [node1] => (item=server1) => {
    "msg": "The server name is: {u'disks': u'3gb', u'ram': u'15Gb', u'name': u'server1', u'network': {u'nic02': u'10Gb', u'nic01': u'100Gb'}}"
}
ok: [node1] => (item=server2) => {
    "msg": "The server name is: {u'disks': u'3gb', u'ram': u'15Gb', u'name': u'server2', u'network': {u'nic02': u'10Gb', u'nic01': u'100Gb'}}"
}

PLAY RECAP **************************************************************************************************************
node1                      : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

效果图如下：

可以看到标签信息已经变了，如item=server1、item=server2，这个时候没有像默认那样显示非常多的信息了，说明标签控制起作用了。

6.2 循环内部暂停

可以使用pause关键字来控制暂停的秒数。

编写剧本文件loop_pause.yml:

- hosts: node1
  tasks:
    - name: Show servers info
      ansible.builtin.command:
        cmd: 'echo "The server name is: {{ item.name }}."'
      loop:
        - name: server1
          disks: 3gb
          ram: 15Gb
          network:
            nic01: 100Gb
            nic02: 10Gb

        - name: server2
          disks: 3gb
          ram: 15Gb
          network:
            nic01: 100Gb
            nic02: 10Gb
      loop_control:
        label: "{{ item.name }}"
        # 暂停30秒
        pause: 30

执行剧本：

[ansible@master ansible_playbooks]$ ansible-lint loop_pause.yml
[ansible@master ansible_playbooks]$ ansible-playbook loop_pause.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ************************************************************************************************************

TASK [Gathering Facts] **************************************************************************************************
ok: [node1]

TASK [Show servers info] ************************************************************************************************
changed: [node1] => (item=server1) => {"ansible_loop_var": "item", "changed": true, "cmd": ["echo", "The server name is: server1."], "delta": "0:00:00.011319", "end": "2023-09-05 22:21:42.923280", "item": {"disks": "3gb", "name": "server1", "network": {"nic01": "100Gb", "nic02": "10Gb"}, "ram": "15Gb"}, "rc": 0, "start": "2023-09-05 22:21:42.911961", "stderr": "", "stderr_lines": [], "stdout": "The server name is: server1.", "stdout_lines": ["The server name is: server1."]}
changed: [node1] => (item=server2) => {"ansible_loop_var": "item", "changed": true, "cmd": ["echo", "The server name is: server2."], "delta": "0:00:00.011203", "end": "2023-09-05 22:22:13.215488", "item": {"disks": "3gb", "name": "server2", "network": {"nic01": "100Gb", "nic02": "10Gb"}, "ram": "15Gb"}, "rc": 0, "start": "2023-09-05 22:22:13.204285", "stderr": "", "stderr_lines": [], "stdout": "The server name is: server2.", "stdout_lines": ["The server name is: server2."]}

PLAY RECAP **************************************************************************************************************
node1                      : ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

效果图：

可以看到，循环第一个item时，中间明显有等待效果，第二个item并没有马上显示出来。

过了段时间后，第二个item也显示出来了：

观察输出结果中的start值，服务器server1的输出值是"start": "2023-09-05 22:21:42.911961"，约为22:21:43, 服务器server2的输出值是"start": "2023-09-05 22:22:13.204285"，约为22:22:13，两者相差30秒，说明循环中间真的是暂停了30秒钟了。

6.3 设置索引

To keep track of where you are in a loop, use the index_var directive with loop_control. This directive specifies a variable name to contain the current loop index.

要跟踪循环中的位置，请使用带有loop_control的index_var指令。 该指令指定一个变量名来包含当前循环索引。

也就是通过index_var来指定循环中索引使用的变量名称，通过该变量，就可以获取索引值。

• 索引默认从0开始计算。

请看下示例，编写剧本文件loop_index.yml:

- hosts: node1
  tasks:
    - name: Count our fruit
      ansible.builtin.debug:
        msg: "{{ item }} with index {{ my_idx }}"
      loop:
        - apple
        - banana
        - pear
      loop_control:
        index_var: my_idx

执行剧本：

[ansible@master ansible_playbooks]$ ansible-lint loop_index.yml
[ansible@master ansible_playbooks]$ ansible-playbook loop_index.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ************************************************************************************************************

TASK [Gathering Facts] **************************************************************************************************
ok: [node1]

TASK [Count our fruit] **************************************************************************************************
ok: [node1] => (item=apple) => {
    "msg": "apple with index 0"
}
ok: [node1] => (item=banana) => {
    "msg": "banana with index 1"
}
ok: [node1] => (item=pear) => {
    "msg": "pear with index 2"
}

PLAY RECAP **************************************************************************************************************
node1                      : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

可以看到，依次输出apple with index 0、banana with index 1、pear with index 2，循环中的索引值从0开始，依次是1、2等等。

6.4 扩展循环变量

As of Ansible 2.8 you can get extended loop information using the extended option to loop control. This option will expose the following information.

从Ansible 2.8版本开始，你可以配置extended选项然后获取扩展循环变量信息。

loop_control:
  extended: true

包括以下变量信息：

序号	变量	说明
1	ansible_loop.allitems	循环列表中所有的元素组成的列表
2	ansible_loop.index	当前索引号（从1开始计算索引）
3	ansible_loop.index0	当前索引号（从0开始计算索引）
4	ansible_loop.revindex	反向索引，当前索引号（从1开始计算索引）
5	ansible_loop.revindex0	反向索引，当前索引号（从0开始计算索引）
6	ansible_loop.first	第一个元素
7	ansible_loop.last	最后一个元素
8	ansible_loop.length	循环列表长度
9	ansible_loop.previtem	前一个元素
10	ansible_loop.nextitem	后一个元素

我们来测试一下。

查看ansible版本信息：

[ansible@master ~]$ ansible --version
ansible 2.9.27
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/home/ansible/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/site-packages/ansible
  executable location = /bin/ansible
  python version = 2.7.5 (default, Nov 16 2020, 22:23:17) [GCC 4.8.5 20150623 (Red Hat 4.8.5-44)]
[ansible@master ~]$

当前ansible版本是ansible 2.9.27，说明支持扩展循环变量。

编写剧本文件loop_extended.yml:

- hosts: node1
  tasks:
    - name: List our programming languages
      ansible.builtin.debug:
        msg: |
          The {{ ansible_loop.index }} language is {{ item }}.
          The length is {{ ansible_loop.length }}.
          The list is {{ ansible_loop.allitems }}.
          The previous item is {{ ansible_loop.previtem }}.
          The following item is {{ ansible_loop.nextitem }}.
      loop:
        - Java
        - Python
        - C++
        - C
        - Golang
        - PHP
      when: 1 < ansible_loop.index < ansible_loop.length
      loop_control:
        extended: true

检查并运行剧本：

[ansible@master ansible_playbooks]$ ansible-lint loop_extended.yml
[ansible@master ansible_playbooks]$ ansible-playbook loop_extended.yml -v
Using /etc/ansible/ansible.cfg as config file

PLAY [node1] ***********************************************************************************************************

TASK [Gathering Facts] *************************************************************************************************
ok: [node1]

TASK [List our programming languages] **********************************************************************************
skipping: [node1] => (item=Java)  => {"ansible_loop": {"allitems": ["Java", "Python", "C++", "C", "Golang", "PHP"], "first": true, "index": 1, "index0": 0, "last": false, "length": 6, "nextitem": "Python", "revindex": 6, "revindex0": 5}, "ansible_loop_var": "item", "item": "Java"}
ok: [node1] => (item=Python) => {
    "msg": "The 2 language is Python.\nThe length is 6.\nThe list is [u'Java', u'Python', u'C++', u'C', u'Golang', u'PHP'].\nThe previous item is Java.\nThe following item is C++.\n"
}
ok: [node1] => (item=C++) => {
    "msg": "The 3 language is C++.\nThe length is 6.\nThe list is [u'Java', u'Python', u'C++', u'C', u'Golang', u'PHP'].\nThe previous item is Python.\nThe following item is C.\n"
}
ok: [node1] => (item=C) => {
    "msg": "The 4 language is C.\nThe length is 6.\nThe list is [u'Java', u'Python', u'C++', u'C', u'Golang', u'PHP'].\nThe previous item is C++.\nThe following item is Golang.\n"
}
ok: [node1] => (item=Golang) => {
    "msg": "The 5 language is Golang.\nThe length is 6.\nThe list is [u'Java', u'Python', u'C++', u'C', u'Golang', u'PHP'].\nThe previous item is C.\nThe following item is PHP.\n"
}
skipping: [node1] => (item=PHP)  => {"ansible_loop": {"allitems": ["Java", "Python", "C++", "C", "Golang", "PHP"], "first": false, "index": 6, "index0": 5, "last": true, "length": 6, "previtem": "Golang", "revindex": 1, "revindex0": 0}, "ansible_loop_var": "item", "item": "PHP"}

PLAY RECAP *************************************************************************************************************
node1                      : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

[ansible@master ansible_playbooks]$

运行效果图：

可以看到，当循环第一个元素Java时，并没有previtem属性，但有nextitem属性，其值是第二个元素Python，当循环到最后一个元素PHP时，没有nextitem属性，但有previtem属性，其值是第五个元素Golang。为了让剧本能够正常运行，特意加了条件判断when: 1 < ansible_loop.index < ansible_loop.length，如果不加该条件判断的话，在循环第一个元素Java时，会提示previtem属性不存在异常。

7. 从with_X迁移至loop

• 在大多数情况下，循环使用loop关键字比使用with_X样式循环效果更好。

此处不详细展开说明，只是罗列官方的几个示例。

7.1 with_list

• with_list可以直接使用loop代替。

- name: with_list
  ansible.builtin.debug:
    msg: "{{ item }}"
  with_list:
    - one
    - two

- name: with_list -> loop
  ansible.builtin.debug:
    msg: "{{ item }}"
  loop:
    - one
    - two

7.2 with_items

• with_items可以使用loop和flatten过滤器代替。

- name: with_items
  ansible.builtin.debug:
    msg: "{{ item }}"
  with_items: "{{ items }}"

- name: with_items -> loop
  ansible.builtin.debug:
    msg: "{{ item }}"
  loop: "{{ items|flatten(levels=1) }}"

其他with_X关键字请参考官方文档 Loops。