Ansible@一个高效的配置管理工具--Ansible configure management--翻译（十）

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Custom ModulesUntil now we have been working solely with the tools provided to us by Ansible.This does afford us a lot of power, and make many things possible. However, if youhave something particularly complex or if you find yourself using the script modulea lot, you will probably want to learn how to extend Ansible.In this chapter you will learn the following topics:• How to write modules in Bash scripting or Python• Using custom modules that you have developed• Writing a script to use an external data source as an inventoryOften when you approach something complex in Ansible, you write a script module.The issue with script modules is that you can't process their output, or triggerhandlers based on their output easily. So, although the script module works in somecases, using a module can be better.Use a module instead of writing a script when:• You don't want to run the script every single time• You need to process the output• Your script needs to make facts• You need to send complex variables as arguments

第五章 自定义模块

此前我们一直使用Ansible自带的模块，这已经给我们提供了很多很强的‘自带的电池’，但是如果你有一些特殊又复杂的任务，你可能会希望学习一下如何扩展Anisble。本章你将学习到以下主题：

• 在python或则bash中编写模块
• 使用你开发的自定义模块
• 写一个脚本来利用外部数据源作为设备清单库inventory

当使用Anisble的方法非常复杂的时候，你可能会编写一个脚本模块。脚本模块的缺点是你不能输出他们的执行过程，或则根据他们的输出来出发Handler程序。所以有些时候可以使用脚本模块，有些时候还是使用自带模块会更好！

以下场景不是很适合脚本模块：

• 不要在每次运行的时候都用脚本
• 当需要使用输出结果的时候
• 你的脚本需要fact的时候
• 当需要传递过于复杂的变量作为参数的时候

If you want to start writing modules, you should check ( )out the Ansible repository.If you want your module to work with a particular version, you should also switchto that version to ensure compatibility. The following commands will set you up todevelop modules for Ansible 1.3.0. Checking out the Ansible code gives you accessto a handy script that we will use later to test our modules. We will also make thisscript executable in anticipation of its use later in the chapter.$ git clone (https://github.com/ansible/ansible.git)$ cd ansible$ git checkout v1.3.0$ chmod +x hacking/test-module

在开始写模块之前，你最好检查一下Ansble的版本库，如果你希望你的模块在一个特殊的版本中运行，你需要切换到相应的版本去开发。下面的命令可以让你升级到Ansible1.3.0的开发模块。通过Anisble代码可以找到一个简单的脚本来测试我们的模块。给这个脚本赋于可执行权限，方便后面的章节使用

$ git clone (https://github.com/ansible/ansible.git)
$ cd ansible
$ git checkout v1.3.0
$ chmod +x hacking/test-module

Writing a module in BashAnsible allows you to write modules in any language that you prefer. Althoughmost modules in Ansible work with JSON, you are allowed to use shortcuts if youdon't have any JSON parsing facilities available. Ansible will hand you argumentsin their original key value forms, if they were provided in that format. If complexarguments are provided, you will receive JSON-encoded data. You could parse thisusing something like jsawk ( https://github.com/micha/jsawk ) or jq ( http://stedolan.github.io/jq/ ), but only if they are installed on your remote machine.Ansible doesn't yet have a module that lets you change the hostname of a systemwith the hostname command. So let's write one. We will start just printing thecurrent hostname and then expand the script from there. Here is what that simplemodule looks like:#!/bin/bashHOSTNAME="$(hostname)"echo "hostname=${HOSTNAME}"

在bash中编写模块

Ansible允许你使用你喜欢的任何语言来编写模块，虽然大部分模块使用JSON，但是如果你没有任何JSON解析器的话你还是可以使用简短格式。如果你的参数格式是KEY VALUS形式，Ansible可以处理他们。如果是更加复杂的参数，你会受到JSON编码的数据，你可以使用JSAWK或则JQ来解析，但你要确保你的远程受管主机也安装了他们。

Anisble现在还没有可以改变系统主机名的模块，让我们就从这开始吧！先写一个简单的脚本来显示主机，后面我们再来扩张它。代码如下：

#!/bin/bash
HOSTNAME="$(hostname)"
echo "hostname=${HOSTNAME}"

If you have written Bash scripts before, this should seem extremely basic. Essentiallywhat we are doing is grabbing the hostname and printing it out in a key value form.Now that we have written the first cut of the module, we should test it out.To test the Ansible modules, we use the script that we ran the chmod command onearlier. This command simply runs your module, records the output, and returnsit to you. It also shows how Ansible interpreted the output of the module. Thecommand that we will use looks like the following:ansible/hacking/test-module -m ./hostname

如果你之前有写过bash脚本，你会发现这是很基础的。我们只是获取主机名然后用KEY VALUS的格式打印出来而已。现在我们已经完成了模块的第一个部分，让我们来测试下。

要测试模块的话，我们只需要使用之前赋权的检测脚本。这个命令执行你的模块，记录输出，返回给你。它还展示了Anisble如何解释模块的输出，命令如下：

ansible/hacking/test-module -m ./hostname

The output of the previous command should look like this:* module boilerplate substitution not requested in module, linenumbers will be unaltered***********************************RAW OUTPUThostname=admin01.int.example.com***********************************PARSED OUTPUT{"hostname": "admin01.int.example.com"}Ignore the notice at the top, it does not apply to modules built with bash. You can seethe raw output that our script sent, which looks exactly the way we expected. Thetest script also gives you the parsed output. In our example, we are using the shortoutput format and we can see here that Ansible is correctly interpreting it into theJSON that it normally accepts from modules.

输出类似下面：

* module boilerplate substitution not requested in module, line
numbers will be unaltered
***********************************
RAW OUTPUT
hostname=admin01.int.example.com
***********************************
PARSED OUTPUT
{
"hostname": "admin01.int.example.com"
}

忽略顶部的提示，可以看到我们写的脚本的raw 输出，跟我们预计的一样。测试脚本还解析了我们的输出，在我们的例子中，我们使用简短格式的输出，但是Ansible将他解析成跟其他模块一样的JSON格式的输出。

Let's expand out the module to allow setting the hostname . We should write it sothat it doesn't make any changes unless it is required, and lets Ansible know whetherchanges were made or not. This is actually pretty simple for the small command thatwe are writing. The new script should look something like this:#!/bin/bashset -e# This is potentially dangeroussource ${1}OLDHOSTNAME="$(hostname)"CHANGED="False"if [ ! -z "$hostname" -a "${hostname}x" != "${OLDHOSTNAME}x" ];thenhostname $hostnameOLDHOSTNAME="$hostname"CHANGED="True"fiecho "hostname=${OLDHOSTNAME} changed=${CHANGED}"exit 0

现在，让我们来扩展我们的模块来设置主机名。代码如下：

#!/bin/bash
set -e
# This is potentially dangerous
source ${1}
OLDHOSTNAME="$(hostname)"
CHANGED="False"
if [ ! -z "$hostname" -a "${hostname}x" != "${OLDHOSTNAME}x" ];
then
hostname $hostname
OLDHOSTNAME="$hostname"
CHANGED="True"
fi
echo "hostname=${OLDHOSTNAME} changed=${CHANGED}"
exit 0

The previous script works like this:1. We set Bash's exit on error mode, so that we don't have to deal with errorsfrom hostname. Bash will automatically exit on failure with its exit code. Thiswill signal Ansible that something went wrong.2. We source the argument file. This file is passed from Ansible as the firstargument to the script. It contains the arguments that were sent to ourmodule. Because we are sourcing the file, this could be used to run arbitrarycommands; however, Ansible can already do this, so it's not that much of asecurity issue.3. We collect the old hostname and default CHANGED to False . This allows us tosee if our module needs to perform any changes.4. We check if we were sent a new hostname to set, and check if that hostnameis different from the one that is currently set.5. If both those tests are true, we try to change the hostname, and set CHANGEDto True .6. Finally, we output the results and exit. This includes the current hostnameand whether we made changes or not.

上面的脚本执行了下面的操作：

1. 我们设定bash在遇到错误的时候退出，所以我们不想要处理来至hostname的错误，bash会自动退出，并输出退出代码，可以让Ansible知道发生错误了。
2. 我们source参数文件，它作为这个脚本的第一个参数，我们可以用其他的命令来source，但是既然Ansible可以做到，就可以为我们减少许多安全隐患。
3. 我们获取原来的hostname并设置CHANGED为faulse，这可以让我们的模块决定是否需要执行更改操作
4. 我们检查是否有新的hostname被设置，并且和旧的hostname不一样
5. 如果2个条件（changed参数和hostname是否重复）都为真，就设置CHANGED参数为True
6. 最后输出结果，然后退出。输出结果包含机器名是否已经被改变。

Changing the hostname on a Unix machine requires root privileges. So while testingthis script, you need to make sure to run it as the root user. Let's test this script usingsudo to see if it works. This is the command you will use:sudo ansible/hacking/test-module -m ./hostname -a'hostname=test.example.com'If test.example.com is not the current hostname of the machine, you should get thefollowing as the output:* module boilerplate substitution not requested in module, linenumbers will be unaltered***********************************RAW OUTPUThostname=test.example.com changed=True***********************************PARSED OUTPUT{"changed": true,"hostname": "test.example.com"}

在unix机器上修改hostname需要root权限，所以测试后脚本的时候，我们需要使用root用户来运行，测试命令如下：

sudo ansible/hacking/test-module -m ./hostname -a  'hostname=test.example.com'  

如果当前主机名不是test.example.com，你将得到如下输出：

* module boilerplate substitution not requested in module, line
numbers will be unaltered
***********************************
RAW OUTPUT
hostname=test.example.com changed=True
***********************************
PARSED OUTPUT
{
"changed": true,
"hostname": "test.example.com"
}

As you can see, our output is being parsed correctly, and the module claims thatchanges have been made to the system. You can check this yourself with thehostname command. Now, run the module for the second time with the samehostname. You should see an output that looks like this:* module boilerplate substitution not requested in module, linenumbers will be unaltered***********************************RAW OUTPUThostname=test.example.com changed=False***********************************PARSED OUTPUT{"changed": false,"hostname": "test.example.com"}Again, we see that the output was parsed correctly. This time, however, the moduleclaims to not have made any changes, which is what we expect. You can also checkthis with the hostname command.

我们的输出被解析的很好，并且模块也使得改变被应用到系统上。你可以用hostname来检查。现在，使用同样的hostname再运行一次脚本，输出如下：

* module boilerplate substitution not requested in module, line
numbers will be unaltered
***********************************
RAW OUTPUT
hostname=test.example.com changed=False
***********************************
PARSED OUTPUT
{
"changed": false,
"hostname": "test.example.com"
}

输出还是被解析的很好，但是模块没有做任何改变，你可以用hostname再检查一次