Ansible 源碼解析： Ansible的運行過程

（本文基於Ansible 2.7）
Ansible的程序入口在bin目錄下，此目錄下共有

• ansible
• ansible-config
• ansible-connection
• ansible-console
• ansible-doc
• ansible-galaxy
• ansible-inventory
• ansible-playbook
• ansible-pull
• ansible-test
• ansible-vault

這11個文件，其中，除ansible、ansible-connection和ansible-test之外，均爲指向ansible的鏈接
下面我們來看ansible的__main__函數：
bin/ansible ,73-118行：

    cli = None
    me = os.path.basename(sys.argv[0])

    try:
        display = Display()
        display.debug("starting run")

        sub = None
        target = me.split('-')
        if target[-1][0].isdigit():
            # Remove any version or python version info as downstreams
            # sometimes add that
            target = target[:-1]

        if len(target) > 1:
            sub = target[1]
            myclass = "%sCLI" % sub.capitalize()
        elif target[0] == 'ansible':
            sub = 'adhoc'
            myclass = 'AdHocCLI'
        else:
            raise AnsibleError("Unknown Ansible alias: %s" % me)

        try:
            mycli = getattr(__import__("ansible.cli.%s" % sub, fromlist=[myclass]), myclass)
        except ImportError as e:
            # ImportError members have changed in py3
            if 'msg' in dir(e):
                msg = e.msg
            else:
                msg = e.message
            if msg.endswith(' %s' % sub):
                raise AnsibleError("Ansible sub-program not implemented: %s" % me)
            else:
                raise

        try:
            args = [to_text(a, errors='surrogate_or_strict') for a in sys.argv]
        except UnicodeError:
            display.error('Command line args are not in utf-8, unable to continue.  Ansible currently only understands utf-8')
            display.display(u"The full traceback was:\n\n%s" % to_text(traceback.format_exc()))
            exit_code = 6
        else:
            cli = mycli(args)
            cli.parse()
            exit_code = cli.run()

我們看到，這裏取了文件名，並以“-”爲分隔符分割，根據“-”後面的部分決定使用哪個CLI。如果分割後的集合長度不大於1（即僅有ansible），默認使用AdHocCLI。
這些CLI的實現在lib/ansible/cli目錄下，均繼承自ansible.cli.CLI（lib/ansible/cli/__init__.py），需實現ansible.cli.CLI的抽象方法run。基類的run方法如下：

lib/ansible/cli/__init__.py，157-181行

    @abstractmethod
    def run(self):
        """Run the ansible command

        Subclasses must implement this method.  It does the actual work of
        running an Ansible command.
        """

        display.vv(to_text(self.parser.get_version()))

        if C.CONFIG_FILE:
            display.v(u"Using %s as config file" % to_text(C.CONFIG_FILE))
        else:
            display.v(u"No config file found; using defaults")

        # warn about deprecated config options
        for deprecated in C.config.DEPRECATED:
            name = deprecated[0]
            why = deprecated[1]['why']
            if 'alternatives' in deprecated[1]:
                alt = ', use %s instead' % deprecated[1]['alternatives']
            else:
                alt = ''
            ver = deprecated[1]['version']
            display.deprecated("%s option, %s %s" % (name, why, alt), version=ver)

沒做什麼實際的事情。而AdHocCLI中的run實現如下：
lib/ansible/cli/adhoc.py，94-188行:

    def run(self):
        ''' create and execute the single task playbook '''

        super(AdHocCLI, self).run()

        # only thing left should be host pattern
        pattern = to_text(self.args[0], errors='surrogate_or_strict')

        sshpass = None
        becomepass = None

        self.normalize_become_options()
        (sshpass, becomepass) = self.ask_passwords()
        passwords = {'conn_pass': sshpass, 'become_pass': becomepass}

        # dynamically load any plugins
        get_all_plugin_loaders()

        loader, inventory, variable_manager = self._play_prereqs(self.options)

        try:
            hosts = CLI.get_host_list(inventory, self.options.subset, pattern)
        except AnsibleError:
            if self.options.subset:
                raise
            else:
                hosts = []
                display.warning("No hosts matched, nothing to do")

        if self.options.listhosts:
            display.display('  hosts (%d):' % len(hosts))
            for host in hosts:
                display.display('    %s' % host)
            return 0

        if self.options.module_name in C.MODULE_REQUIRE_ARGS and not self.options.module_args:
            err = "No argument passed to %s module" % self.options.module_name
            if pattern.endswith(".yml"):
                err = err + ' (did you mean to run ansible-playbook?)'
            raise AnsibleOptionsError(err)

        # Avoid modules that don't work with ad-hoc
        if self.options.module_name in ('import_playbook',):
            raise AnsibleOptionsError("'%s' is not a valid action for ad-hoc commands" % self.options.module_name)

        play_ds = self._play_ds(pattern, self.options.seconds, self.options.poll_interval)
        play = Play().load(play_ds, variable_manager=variable_manager, loader=loader)

        # used in start callback
        playbook = Playbook(loader)
        playbook._entries.append(play)
        playbook._file_name = '__adhoc_playbook__'

        if self.callback:
            cb = self.callback
        elif self.options.one_line:
            cb = 'oneline'
        # Respect custom 'stdout_callback' only with enabled 'bin_ansible_callbacks'
        elif C.DEFAULT_LOAD_CALLBACK_PLUGINS and C.DEFAULT_STDOUT_CALLBACK != 'default':
            cb = C.DEFAULT_STDOUT_CALLBACK
        else:
            cb = 'minimal'

        run_tree = False
        if self.options.tree:
            C.DEFAULT_CALLBACK_WHITELIST.append('tree')
            C.TREE_DIR = self.options.tree
            run_tree = True

        # now create a task queue manager to execute the play
        self._tqm = None
        try:
            self._tqm = TaskQueueManager(
                inventory=inventory,
                variable_manager=variable_manager,
                loader=loader,
                options=self.options,
                passwords=passwords,
                stdout_callback=cb,
                run_additional_callbacks=C.DEFAULT_LOAD_CALLBACK_PLUGINS,
                run_tree=run_tree,
            )

            self._tqm.send_callback('v2_playbook_on_start', playbook)

            result = self._tqm.run(play)

            self._tqm.send_callback('v2_playbook_on_stats', self._tqm._stats)
        finally:
            if self._tqm:
                self._tqm.cleanup()
            if loader:
                loader.cleanup_all_tmp_files()

        return result

可以看到，也是使用TaskQueueManager去組織和運行任務的，與Ansible API介紹的方式等同。