Understand ansible architecture and working principles

Ansible is a model-driven configuration manager that supports multi-node publishing and remote task execution. By default, SSH is used for remote connections. There is no need to install additional software on managed nodes and it can be extended using a variety of programming languages.

1. Ansible basic architecture

The picture above shows the basic architecture of ansible. From the picture above, you can understand that it consists of the following parts:

• Core: ansible
• Core Modules: These are the modules that come with ansible
• Extension modules (Custom Modules): If the core module is not enough to complete a certain function, you can add extension modules
• Plugins: Complete the supplement of module functions
• Playbooks: Ansible's task configuration file, which defines multiple tasks in the playbook and is automatically executed by ansible
• Connectior Plugins: ansible connects to each host based on connection plug-ins. Although ansible uses ssh to connect to each host, it also supports other connection methods, so a connection plug-in is required
• Host Inventory: Define the hosts managed by ansible

2. Working principle of ansible

The above are two ansible working principle diagrams found on the Internet. Both diagrams are basically expansions based on the architecture diagram. You can understand from the picture above:

1. The management terminal supports three ways to connect to the managed terminal: local, ssh, and zeromq. The default is to use the ssh-based connection---this part corresponds to the connection module in the basic architecture diagram;

2. Host Inventory (host group) can be classified according to application type, etc. The management node implements corresponding operations through various modules - a single module, batch execution of a single command, we can call it ad-hoc ;

3. The management node can use playbooks to implement a collection of multiple tasks to implement a type of functions, such as the installation and deployment of web services, batch backup of database servers, etc. We can simply understand playbooks as configuration files that the system operates by combining multiple ad-hoc operations.

3. Seven commands of ansible

After installing ansible, we found that ansible provides us with seven instructions in total: ansible, ansible-doc, ansible-galaxy, ansible-lint, ansible-playbook, ansible-pull, ansible-vault. Here we only look at the usage part, and the detailed part can be obtained through the "command -h" method.

1. ansible

1.[root@localhost ~]# ansible -h
2.Usage: ansible  [options]

Ansible is the core part of the command, which is mainly used to execute ad-hoc commands, that is, a single command. By default, the host and options parts need to be followed. When the module is not specified by default, the command module is used. Such as:

1.[root@361way.com ~]# ansible 192.168.0.102 -a 'date'
2192.168.0.102 | success | rc=0 >>
3Tue May 12 22:57:24 CST 2015

However, the default module can be modified in ansible.cfg. The parameters under the ansible command are explained as follows:

1. Parameters:
2. -a 'Arguments', --args='Arguments' command line parameters
3. -m NAME, --module-name=NAME The name of the execution module. The command module is used by default, so if you only execute a single command, you do not need the -m parameter
4. -i PATH, --inventory=PATH specifies the path to the inventory host file, the default is /etc/ansible/hosts.
5. -u Username, --user=Username execution user, use this remote username instead of the current user
6. -U --sud-user=SUDO_User Which user to sudo to, the default is root
7. -k --ask-pass login password, prompt for SSH password instead of assuming key-based authentication
8. -K --ask-sudo-pass prompts for password use sudo
9. -s --sudo sudo run
10. -S --su Use su command
11. -l --list displays all supported modules
12. -s --snippet specifies the module to display script snippets
13. -f --forks=NUM Number of parallel tasks. NUM is specified as an integer, the default is 5. #ansible testhosts -a "/sbin/reboot" -f 10 Restart all machines in the testhosts group, 10 machines at a time
14. --private-key=PRIVATE_KEY_FILE private key path, use this file to verify the connection
15. -v --verbose details
16. all executes
for all hosts defined by hosts
17. -M MODULE_PATH, --module-path=MODULE_PATH The path of the module to be executed, the default is /usr/share/ansible/
18. --list-hosts only prints which hosts will execute this playbook file, not actually executes the playbook file
19. -o --one-line compressed output, summarized output. Try to output everything on one line.
20. -t Directory, --tree=Directory Save the contents in this output directory, saving the results in a file on each host.
21. -B background running timeout
22. -P Investigate background program time
23. -T Seconds, --timeout=Seconds time in seconds
24. -P NUM, --poll=NUM Poll background work every few seconds. Required - b
25. -c Connection, --connection=Connection connection type to use. Possible options are paramiko(SSH), SSH and local. Local is mainly used for crontab or startup.
26. --tags=TAGS Only execute the task with the specified tags Example: ansible-playbook test.yml --tags=copy Only execute the task with the tag copy
27. --list-hosts only prints which hosts will execute this playbook file, not actually executes the playbook file
28. --list-tasks List all tasks that will be executed
29. -C, --check just tests what will be changed and will not actually execute it; instead, it tries to predict some possible changes
30. --syntax-check Perform syntax check of the script, but do not execute it
31. -l SUBSET, --limit=SUBSET further limit the selected host/group mode --limit=192.168.0.15 Only execute this ip
32. --skip-tags=SKIP_TAGS Only run plays and tasks with tags that do not match these values ​​--skip-tags=copy_start
33. -e EXTRA_VARS, --extra-vars=EXTRA_VARS Extra variables set as key=value or YAML/JSON
34. #cat update.yml
35. ---
36. - hosts: {{ hosts }}
37. remote_user: {{ user }}
38. ............
39. #ansible-playbook update.yml --extra-vars "hosts=vipers user=admin" Pass {{hosts}}, {{user}} variables, hosts can be ip or group name
40. -l,--limit Execute tasks on the specified host/group--limit=192.168.0.10, 192.168.0.11 or -l 192.168.0.10, 192.168.0.11 Execute tasks only on these 2 IPs

2. ansible-doc

# ansible-doc -h
Usage: ansible-doc [options] [module...]

该指令用于查看模块信息，常用参数有两个-l 和 -s ，具体如下：

1. //列出所有已安装的模块
2. # ansible-doc -l
3. //查看具体某模块的用法，这里如查看command模块
4. # ansible-doc -s command

3、ansible-galaxy

# ansible-galaxy -h
Usage: ansible-galaxy [init|info|install|list|remove] [--help] [options] ...

ansible-galaxy 指令用于方便的从https://galaxy.ansible.com/ 站点下载第三方扩展模块，我们可以形象的理解其类似于centos下的yum、python下的pip或easy_install 。如下示例：

[root@localhost ~]# ansible-galaxy install aeriscloud.docker
- downloading role 'docker', owned by aeriscloud
- downloading role from https://github.com/AerisCloud/ansible-docker/archive/v1.0.0.tar.gz
- extracting aeriscloud.docker to /etc/ansible/roles/aeriscloud.docker
- aeriscloud.docker was installed successfully

这个安装了一个aeriscloud.docker组件，前面aeriscloud是galaxy上创建该模块的用户名，后面对应的是其模块。在实际应用中也可以指定txt或yml 文件进行多个组件的下载安装。这部分可以参看官方文档。

4、ansible-lint

ansible-lint是对playbook的语法进行检查的一个工具。用法是ansible-lint playbook.yml 。

5、ansible-playbook

该指令是使用最多的指令，其通过读取playbook 文件后，执行相应的动作，这个后面会做为一个重点来讲。

6、ansible-pull

该指令使用需要谈到ansible的另一种模式－－－pull 模式，这和我们平常经常用的push模式刚好相反，其适用于以下场景：你有数量巨大的机器需要配置，即使使用非常高的线程还是要花费很多时间；你要在一个没有网络连接的机器上运行Anisble，比如在启动之后安装。这部分也会单独做一节来讲。

7、ansible-vault

ansible-vault主要应用于配置文件中含有敏感信息，又不希望他能被人看到，vault可以帮你加密/解密这个配置文件，属高级用法。主要对于playbooks里比如涉及到配置密码或其他变量时，可以通过该指令加密，这样我们通过cat看到的会是一个密码串类的文件，编辑的时候需要输入事先设定的密码才能打开。这种playbook文件在执行时，需要加上 --ask-vault-pass参数，同样需要输入密码后才能正常执行。具体该部分可以参查官方博客。

注：上面七个指令，用的最多的只有两个ansible 和ansible-playbook ，这两个一定要掌握，其他五个属于拓展或高级部分。

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