如果您想要一组足够灵活的任务来支持多个 Linux
包管理器和 macOS brew，选择更多逻辑或更多
重复。
这三种模式应该会有所帮助。他们仍然有重复和
样板代码，但这是我们使用 Ansible 的领域
跨平台。
- 仅针对 Linux 全局声明
become: yes (root)
- 使用
when 解决需要根据需要进行平台特定处理的包
- 这可能是
--head 用于brew，或者为apt 设置PPA，等等
- 映射包名称与变量的差异
- 例如：
brew install ncurses、apt install libncurses5-dev 和 dnf install ncurses-devel 都是同一个库。
1) 仅针对 Linux 全局声明 become: yes (root)
对于 Linux 主机，切换到 root 进行安装是预期的行为。
对于 macOS a la Homebrew，以 root 身份安装并不好。所以，我们在使用brew 时需要become: no (false)，否则使用become: yes (true)（对于
Linux）。
在您的示例中，become 指令嵌套在每个任务（“步骤”）中。到
防止重复，在任务之前在更高的词法范围调用become
开始。随后的任务就会继承become的状态，也就是
根据条件表达式设置。
不幸的是，在根剧本范围内become 的变量将是
undefined 并在第一个任务运行前抛出错误：
# playbook.yml
- name: Demo
hosts: localhost
connection: local
# This works
become: True
# This doesn't - the variable is undefined
become: "{{ False if ansible_pkg_mgr == 'brew' else True }}"
# Nor does this - also undefined
become: "{{ False if ansible_os_family == 'Darwin' else True }}"
tasks:
# ...
要解决这个问题，我们可以将任务存储在另一个文件中并import 他们，或者
将任务包装在 block 中。这些模式中的任何一个都将提供
有机会及时用我们的自定义变量值声明become
接任务：
# playbook.yml
---
- name: Demo
hosts: localhost
connection: local
vars:
# This variable gives us a boolean for deciding whether or not to become
# root. It cascades down to any subsequent tasks unless overwritten.
should_be_root: "{{ true if ansible_pkg_mgr != 'brew' else false }}"
# It could also be based on the OS type, but since brew is the main cause
# it's probably better this way.
# should_be_root: "{{ False if ansible_os_family == 'Darwin' else True }}"
tasks:
# Import the tasks from another file, which gives us a chance to pass along
# a `become` context with our variable:
- import_tasks: test_tasks.yml
become: "{{ should_be_root }}"
# Wrapping the tasks in a block will also work:
- block:
- name: ncurses is present
package:
name: [libncurses5-dev, libncursesw5-dev]
state: present
- name: cmatrix is present
package:
name: cmatrix
state: present
become: "{{ should_be_root }}"
现在有一个brew 的逻辑检查和一个before 指令
（取决于上面使用的任务模式）。所有任务将被执行为
root 用户，除非正在使用的包管理器是 brew。
2) 使用when 按需处理需要特定平台处理的包
Package Module 非常方便，但功能有限。经过
它本身只适用于理想场景；意思是，一个不
需要来自底层包管理器的任何特殊处理或标志。全部
它可以做的是传递要安装的包的文字字符串state，以及
强制使用特定包管理器可执行文件的可选参数。
这是一个安装 wget 的示例，它带有一个不错的简短任务，并且只会变成
与brew 一起安装时处理ffmpeg 的特殊情况的详细信息：
# playbook.yml
# ...
tasks:
# wget is the same among package managers, nothing to see here
- name: wget is present
when: ansible_pkg_mgr != 'brew'
package:
name: wget
state: present
# This will only run on hosts that do not use `brew`, like linux
- name: ffmpeg is present
when: ansible_pkg_mgr != 'brew'
package:
name: ffmpeg
state: present
# This will only run on hosts that use `brew`, i.e. macOS
- name: ffmpeg is present (brew)
when: ansible_pkg_mgr == 'brew'
homebrew:
name: ffmpeg
# head flag
state: head
# --with-chromaprint --with-fdk-aac --with-etc-etc
install_options: with-chromaprint, with-fdk-aac, with-etc-etc
上面的游戏会针对 Linux 机器产生 ffmpeg 的输出：
TASK [youtube-dl : ffmpeg is present] ******************************************
ok: [localhost]
TASK [youtube-dl : ffmpeg is present (brew)] ***********************************
skipping: [localhost]
3) 映射包名与变量的差异
这不是您问题的具体部分，但很可能会出现在下一个问题中。
Package Module 文档还提到：
包名称也因包管理器而异；这个模块不会“翻译”
他们每个发行版。例如 libyaml-dev、libyaml-devel。
因此，我们自行处理相同软件使用不同的情况
包管理器平台之间的名称。这很常见。
对此有多种模式，例如：
他们都不是很愉快。这是使用role 的方法。角色做
涉及更多样板和目录杂耍，但作为交换，它们提供
模块化和局部变量环境。当一个角色中的一组任务
需要更多的技巧才能正确，它最终不会污染其他任务
套。
# playbook.yml
---
- name: Demo
hosts: localhost
connection: local
roles:
- cmatrix
# roles/cmatrix/defaults/main.yml
---
ncurses:
default:
- ncurses
# Important: these keys need to exactly match the name of package managers for
# our logic to hold up
apt:
- libncurses5-dev
- libncursesw5-dev
brew:
- pkg-config
- ncurses
# roles/cmatrix/tasks/main.yml
---
- name: cmatix and its dependencies are present
become: "{{ should_be_root }}"
block:
- name: ncurses is present
package:
name: '{{ item }}'
state: latest
loop: "{{ ncurses[ansible_pkg_mgr] | default(ncurses['default']) }}"
- name: cmatrix is present
when: ansible_pkg_mgr != 'brew'
package:
name: cmatrix
state: present
ncurses 的任务会查找一组项以循环遍历
对应的包管理器。如果未定义正在使用的包管理器
在变量对象中，使用 Jinja 默认过滤器来引用
default 我们设置的值。
使用此模式，添加对另一个包管理器的支持或其他
依赖项只涉及更新变量对象：
# roles/cmatrix/defaults/main.yml
---
ncurses:
default:
- ncurses
apt:
- libncurses5-dev
- libncursesw5-dev
# add a new dependency for Debian
- imaginarycurses-dep
brew:
- pkg-config
- ncurses
# add support for Fedora
dnf:
- ncurses-devel
将所有内容组合成真正的游戏
这是一个涵盖所有三个方面的完整示例。剧本有两个作用
每个人都使用基于单个变量的正确 become 值。它也是
安装时包含cmatrix 和ffmpeg 的特殊情况
brew，并处理包管理器之间 ncurses 的备用名称。
# playbook.yml
---
- name: Demo
hosts: localhost
connection: local
vars:
should_be_root: "{{ true if ansible_pkg_mgr != 'brew' else false }}"
roles:
- cmatrix
- youtube-dl
# roles/cmatrix/defaults/main.yml
ncurses:
default:
- ncurses
apt:
- libncurses5-dev
- libncursesw5-dev
brew:
- pkg-config
- ncurses
dnf:
- ncurses-devel
# roles/cmatrix/tasks/main.yml
---
- name: cmatrix and dependencies are present
# A var from above, in the playbook
become: "{{ should_be_root }}"
block:
- name: ncurses is present
package:
name: '{{ item }}'
state: latest
# Get an array of the correct package names to install from the map in our
# default variables file
loop: "{{ ncurses[ansible_pkg_mgr] | default(ncurses['default']) }}"
# Install as usual if this is not a brew system
- name: cmatrix is present
when: ansible_pkg_mgr != 'brew'
package:
name: cmatrix
state: present
# If it is a brew system, use this instead
- name: cmatrix is present (brew)
when: ansible_pkg_mgr == 'brew'
homebrew:
name: cmatrix
state: head
install_options: with-some-option
# roles/youtube-dl/tasks/main.yml
---
- name: youtube-dl and dependencies are present
become: "{{ should_be_root }}"
block:
- name: ffmpeg is present
when: ansible_pkg_mgr != 'brew'
package:
name: ffmpeg
state: latest
- name: ffmpeg is present (brew)
when: ansible_pkg_mgr == 'brew'
homebrew:
name: ffmpeg
state: head
install_options: with-chromaprint, with-fdk-aac, with-etc-etc
- name: atomicparsley is present
package:
name: atomicparsley
state: latest
- name: youtube-dl is present
package:
name: youtube-dl
state: latest
Ubuntu 的结果：
$ ansible-playbook demo.yml
[WARNING]: provided hosts list is empty, only localhost is available. Note that
the implicit localhost does not match 'all'
PLAY [Demo] ********************************************************************
TASK [Gathering Facts] *********************************************************
ok: [localhost]
TASK [cmatrix : ncurses is present] ********************************************
ok: [localhost] => (item=libncurses5-dev)
ok: [localhost] => (item=libncursesw5-dev)
TASK [cmatrix : cmatrix is present] ********************************************
ok: [localhost]
TASK [cmatrix : cmatrix is present (brew)] *************************************
skipping: [localhost]
TASK [youtube-dl : ffmpeg is present] ******************************************
ok: [localhost]
TASK [youtube-dl : ffmpeg is present (brew)] ***********************************
skipping: [localhost]
TASK [youtube-dl : atomicparsley is present] ***********************************
ok: [localhost]
TASK [youtube-dl : youtube-dl is present] **************************************
ok: [localhost]
PLAY RECAP *********************************************************************
localhost : ok=6 changed=0 unreachable=0 failed=0 skipped=2 rescued=0 ignored=0