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Ansible的Ad-hoc命令执行流程

用了这么久的Ansible，今天想着研究下Ad-hoc命令的执行流程，从最简单的ping开始吧。

测试命令如下：

ansible 172.18.2.31 -m ping

先看看回显的结果

[root@bigdata-m-002 etc]# ansible 172.18.2.31 -m ping
172.18.2.31 | SUCCESS => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}, "changed": false, "ping": "pong"
}

内容很少，加上-vvv查看详细的信息：

[root@bigdata-m-002 etc]# ansible 172.18.2.31 -m ping -vvv
Using /etc/ansible/ansible.cfg as config file
host_list declined parsing /etc/ansible/hosts as it did not pass its verify_file() method
script declined parsing /etc/ansible/hosts as it did not pass its verify_file() method
auto declined parsing /etc/ansible/hosts as it did not pass its verify_file() method
META: ran handlers
<172.18.2.31> Attempting python interpreter discovery
<172.18.2.31> ESTABLISH SSH CONNECTION FOR USER: None
<172.18.2.31> SSH: EXEC ssh -C -o ControlMaster=auto -o ControlPersist=60s -o KbdInteractiveAuthentication=no -o PreferredAuthentications=gssapi-with-mic,gssapi-keyex,hostbased,publickey -o PasswordAuthentication=no -o ConnectTimeout=10 -o ControlPath=/root/.ansible/cp/414e6c60fc 172.18.2.31 '/bin/sh -c '"'"'echo PLATFORM; uname; echo FOUND; command -v '"'"'"'"'"'"'"'"'/usr/bin/python'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python3.7'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python3.6'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python3.5'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python2.7'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python2.6'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'/usr/libexec/platform-python'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'/usr/bin/python3'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python'"'"'"'"'"'"'"'"'; echo ENDFOUND && sleep 0'"'"''
<172.18.2.31> (0, 'PLATFORM\nLinux\nFOUND\n/usr/bin/python\n/usr/bin/python2.7\n/usr/libexec/platform-python\n/usr/bin/python\nENDFOUND\n', '')
<172.18.2.31> ESTABLISH SSH CONNECTION FOR USER: None
<172.18.2.31> SSH: EXEC ssh -C -o ControlMaster=auto -o ControlPersist=60s -o KbdInteractiveAuthentication=no -o PreferredAuthentications=gssapi-with-mic,gssapi-keyex,hostbased,publickey -o PasswordAuthentication=no -o ConnectTimeout=10 -o ControlPath=/root/.ansible/cp/414e6c60fc 172.18.2.31 '/bin/sh -c '"'"'/usr/bin/python && sleep 0'"'"''
<172.18.2.31> (0, '{"osrelease_content": "NAME=\\"CentOS Linux\\"\\nVERSION=\\"7 (Core)\\"\\nID=\\"centos\\"\\nID_LIKE=\\"rhel fedora\\"\\nVERSION_ID=\\"7\\"\\nPRETTY_NAME=\\"CentOS Linux 7 (Core)\\"\\nANSI_COLOR=\\"0;31\\"\\nCPE_NAME=\\"cpe:/o:centos:centos:7\\"\\nHOME_URL=\\"/\\"\\nBUG_REPORT_URL=\\"/\\"\\n\\nCENTOS_MANTISBT_PROJECT=\\"CentOS-7\\"\\nCENTOS_MANTISBT_PROJECT_VERSION=\\"7\\"\\nREDHAT_SUPPORT_PRODUCT=\\"centos\\"\\nREDHAT_SUPPORT_PRODUCT_VERSION=\\"7\\"\\n\\n", "platform_dist_result": ["centos", "7.8.2003", "Core"]}\n', '')
Using module file /usr/lib/python2.7/site-packages/ansible/modules/system/ping.py
Pipelining is enabled.
<172.18.2.31> ESTABLISH SSH CONNECTION FOR USER: None
<172.18.2.31> SSH: EXEC ssh -C -o ControlMaster=auto -o ControlPersist=60s -o KbdInteractiveAuthentication=no -o PreferredAuthentications=gssapi-with-mic,gssapi-keyex,hostbased,publickey -o PasswordAuthentication=no -o ConnectTimeout=10 -o ControlPath=/root/.ansible/cp/414e6c60fc 172.18.2.31 '/bin/sh -c '"'"'/usr/bin/python && sleep 0'"'"''
<172.18.2.31> (0, '\n{"invocation": {"module_args": {"data": "pong"}}, "ping": "pong"}\n', '')
172.18.2.31 | SUCCESS => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python"}, "changed": false, "invocation": {"module_args": {"data": "pong"}}, "ping": "pong"
}
META: ran handlers
META: ran handlers

上述的命令删除了一部分不必要的内容，主要是了解一下整个执行的过程，首先ansible会读取ansible.cfg作为配置文件，这个是默认的配置文件位置，随后ansible读取主机配置文件获得远程服务器的ip信息以及可能存在的变量信息。

接下来，ansible会尝试搜索远程的python解释器，也就是下面的命令：

SSH: EXEC ssh -C -o ControlMaster=auto -o ControlPersist=60s -o KbdInteractiveAuthentication=no -o PreferredAuthentications=gssapi-with-mic,gssapi-keyex,hostbased,publickey -o PasswordAuthentication=no -o ConnectTimeout=10 -o ControlPath=/root/.ansible/cp/414e6c60fc 172.18.2.31 '/bin/sh -c '"'"'echo PLATFORM; uname; echo FOUND; command -v '"'"'"'"'"'"'"'"'/usr/bin/python'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python3.7'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python3.6'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python3.5'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python2.7'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python2.6'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'/usr/libexec/platform-python'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'/usr/bin/python3'"'"'"'"'"'"'"'"'; command -v '"'"'"'"'"'"'"'"'python'"'"'"'"'"'"'"'"'; echo ENDFOUND && sleep 0'"'"''

command -v可以搜寻指定命令的绝对路径，此处搜索的命令清单定义在base.yml文件中：

INTERPRETER_PYTHON_FALLBACK:name: Ordered list of Python interpreters to check for in discoverydefault:- /usr/bin/python- python3.7- python3.6- python3.5- python2.7- python2.6- /usr/libexec/platform-python- /usr/bin/python3- python

接下来Ansible会默认以拿到的第一个python路径作为运行远程脚本的解释器，并以此开启交互页，也就是这个命令的作用：

ssh -C -o ControlMaster=auto -o ControlPersist=60s -o KbdInteractiveAuthentication=no -o PreferredAuthentications=gssapi-with-mic,gssapi-keyex,hostbased,publickey -o PasswordAuthentication=no -o ConnectTimeout=10 -o ControlPath=/root/.ansible/cp/414e6c60fc 172.18.2.31 '/bin/sh -c '"'"'/usr/bin/python && sleep 0'"'"''

这里并没有打印出具体执行的逻辑，只有一个/usr/bin/python，实际上这是一个交互窗口，接下来会在这个交互窗口中执行python脚本的逻辑，首先会执行executor/discovery/python_target.py的逻辑，获取一些操作系统的基本信息：

[root@bigdata-m-002 etc]# python /usr/lib/python2.7/site-packages/ansible/executor/discovery/python_target.py
{"osrelease_content": "NAME=\"CentOS Linux\"\nVERSION=\"7 (Core)\"\nID=\"centos\"\nID_LIKE=\"rhel fedora\"\nVERSION_ID=\"7\"\nPRETTY_NAME=\"CentOS Linux 7 (Core)\"\nANSI_COLOR=\"0;31\"\nCPE_NAME=\"cpe:/o:centos:centos:7\"\nHOME_URL=\"/\"\nBUG_REPORT_URL=\"/\"\n\nCENTOS_MANTISBT_PROJECT=\"CentOS-7\"\nCENTOS_MANTISBT_PROJECT_VERSION=\"7\"\nREDHAT_SUPPORT_PRODUCT=\"centos\"\nREDHAT_SUPPORT_PRODUCT_VERSION=\"7\"\n\n", "platform_dist_result": ["centos", "7.8.2003", "Core"]}

随后就是准备执行模块的业务逻辑了，这里以ping模块为例，在执行具体的模块业务逻辑前，模块依赖的所有脚本文件都会被打包在一个python文件中，类似这样：

[root@bigdata-m-002 ansible-tmp-1699492620.36-27101-107096752350654]# ll
total 112
-rwx------. 1 root root 114480 Nov  9 14:10 AnsiballZ_ping.py

这个脚本的内容会通过定义的标准输入写进交互界面进行执行，如果手动执行就可以看到其回显的结果正是我们执行ansible的时候回显的结果，只不过ansible用自己的回调进行了处理：

[root@bigdata-m-002 ansible-tmp-1699492620.36-27101-107096752350654]# python AnsiballZ_ping.py {"invocation": {"module_args": {"data": "pong"}}, "ping": "pong"}
[root@bigdata-m-002 ansible-tmp-1699492620.36-27101-107096752350654]# 

而这个脚本中有个变量ZIP_DATA，就是把相关依赖文件被转换成了base64加密的一串字符，稍后ansible会将这些字符以文件流的方式再写入zip文件，然后进行解压，从而得到一系列依赖python：

[root@bigdata-m-002 ansible_ping_payload_zNTlb2]# tree
.
├── ansible
│   ├── __init__.py
│   ├── modules
│   │   ├── __init__.py
│   │   └── system
│   │       ├── __init__.py
│   │       └── ping.py
│   └── module_utils
│       ├── basic.py
│       ├── common
│       │   ├── _collections_compat.py
│       │   ├── collections.py
│       │   ├── file.py
│       │   ├── __init__.py
│       │   ├── _json_compat.py
│       │   ├── parameters.py
│       │   ├── process.py
│       │   ├── sys_info.py
│       │   ├── text
│       │   │   ├── converters.py
│       │   │   ├── formatters.py
│       │   │   └── __init__.py
│       │   ├── _utils.py
│       │   └── validation.py
│       ├── compat
│       │   ├── __init__.py
│       │   ├── _selectors2.py
│       │   └── selectors.py
│       ├── distro
│       │   ├── _distro.py
│       │   └── __init__.py
│       ├── __init__.py
│       ├── parsing
│       │   ├── convert_bool.py
│       │   └── __init__.py
│       ├── pycompat24.py
│       ├── six
│       │   └── __init__.py
│       └── _text.py
├── ansible_ping_payload.zip
└── sitecustomize.py

如果去看了ping的实现逻辑，我们就知道ansible的ping其实不是发送icmp包实现的，而是尝试在远程服务器上打印data，不过如果你的data给的值是crash，ansible会给你抛出一个boom的错误：

from ansible.module_utils.basic import AnsibleModuledef main():module = AnsibleModule(argument_spec=dict(data=dict(type='str', default='pong'),),supports_check_mode=True)if module.params['data'] == 'crash':raise Exception("boom")result = dict(ping=module.params['data'],)module.exit_json(**result)if __name__ == '__main__':main()

可能这就是开发人员的恶趣味吧~