Ansible:仅在未定义的情况下设置变量 [英] Ansible: Set variable only if undefined

问题描述

我想将ansible变量设置为某个默认值，但前提是该变量未定义.否则，我想保持不变.

I would like to set an ansible variable to some default value but only if the variable is undefined. Otherwise I would like to keep it unchanged.

我尝试了这两种方法，它们都产生了递归循环:

I tried these two approaches and both of them produce recursive loop:

namespace: "{{namespace|default(default_namespace)}}"
namespace: "{% if namespace is defined %}{{namespace}}{% else %}{{default_namespace}}{% endif %}"

推荐答案

您似乎采取了错误的方法.

It seems like you are taking a wrong approach.

看看有关可变优先级.如果未定义变量，则Ansible的内置功能是使用默认变量.

Take a look at the Ansible documentation concerning variable precedence. It is a built-in feature of Ansible to use the default variable if the variable is not defined.

在Ansible 2.x中，变量优先级如下所示:

In Ansible 2.x the variable precedence starts like this:

角色默认值

库存变量

因此，如果要为变量定义默认值，则应在role/defaults/main.yml中进行设置.仅当未在其他位置定义变量时，Ansible才会使用该值.

So if you want to define a default value for a variable you should set it in role/defaults/main.yml. Ansible will use that value only if the variable is not defined somewhere else.

另一种选择是使用 Jinja2过滤器.使用Jinja过滤器，您可以为这样的变量设置默认值:

Another option is to use a Jinja2 filter. With a Jinja filter you can set a default value for a variable like this:

{{ some_variable | default(5) }}

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