问题描述
场景 ansible-playbook 被调用并传入额外的变量:
Scenario ansible-playbook is called with passed in extra var:
-e my_var=init_value
然后在角色代码中，该值应该通过 set_fact 调用更改(变量 other_var 值为new_value"):
Then in a role code the value is supposed to change via set_fact call (variable other_var value is "new_value"):
set_fact: my_var: {{ other_var }}
这会产生一个很好的输出，据说可以确认更改:
This results in a nice output supposedly confirming alteration:
{"ansible facts": {"my_var": "new_value"}}
但是在更改变量后回显变量显示旧值:
However echoing the variable after changing it shows the old value:
echo {{ my_var }}
-> "echo init_value"
补充一点，当我在上面的例子中设置两个变量时:
To add to that, when I set two variables in the above example:
set_fact: my_var: {{ other_var }}
set_fact: new_var: {{ other_var }}
new_var 设置正确.
The new_var is set properly.
变量在某种程度上是不可变的吗?如何使用 set_fact 更新变量的值?
Is the variable in some way immutable? How to use the set_fact to update the variable's value?
推荐答案
set_fact 模块有效地添加了另一个宿主事实，即.发现的有关系统的事实".从文档(http://docs.ansible.com/playbooks_variables.html#variable-precedence-where-should-i-put-a-variable) 你可以看到这些事实的优先级很低，并且会被 extra-vars 和其他各种覆盖东西.
The set_fact module effectively adds another host fact, ie. "a fact discovered about the system". From the documentation (http://docs.ansible.com/playbooks_variables.html#variable-precedence-where-should-i-put-a-variable) you can see that those facts have low priority, and will be overridden by extra-vars and various other things.
这可能会令人困惑，因为使用 set_fact 会使您看起来好像在那时正在更改变量的值，但也许名称是理解的关键 - 它不是set_variable"，它是set_(host)fact"，并且主机事实具有低优先级.优先级比赋值的顺序更重要.
This can be confusing because using set_fact can make it seem like you are changing the value of the variable at that point, but maybe the name is the key to understanding - it's not 'set_variable', it's 'set_(host)fact', and host facts have low precedence. Precedence is more important than the order in which the value is assigned.
如果您想通过 extra-vars 提供一个稍后被覆盖的值，一种解决方法是通过 set_fact 将该 extra-vars 值重新分配给不同的变量剧本的开始，然后再次使用 set_fact 重新分配该新变量.由于它们具有相同的优先级，因此覆盖"应该按您的预期工作.
One workaround if you want to supply a value via extra-vars that gets overwritten later would be to reassign that extra-vars value to a different variable via set_fact at the start of your playbook, and then reassign that new variable later using set_fact again. Since they're at the same precedence level, the 'overwrite' should work as you would expect.
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