在Jinja2语句中使用Jinja2表达式

Question

Let's say I have the following Jinja2 variables:

• 'dev_ami' = 'ami-123456'
• 'dev_located_ami' = 'ami-123456'
• 'prod_ami' = 'ami-654321'
• 'prod_located_ami' = 'ami-654321'

I would like to set a condition upon when the 'dev_ami' variable is equal to the 'dev_located_ami' variable. This would easily be done as shown in the following statement:

{% if dev_ami == dev_located_ami %}
... do some stuff
{% else %}
... do some other stuff
{% endif %}

But I would like to dynamically compare amis based on the deployment environment contained in a list ['dev','prod', etc...]. The following contains a templating error since there is an expression within a statement as such - {% {{ .. }} %} :

{% for env_type in ['dev','prod'] %}
{% if {{ env_type }}_ami == {{ env_type }}_located_ami %}
... do stuff
{% else %}
... do other stuff
{% endif %}
{% endfor %}

I have tried to set variables to represent the expressions I would like in the following code but unfortunately they are compiled literally as 'dev_ami' and 'dev_located_ami' whereas I would like them compiled to their corresponding variable values 'ami-123456' and 'ami-123456':

{% for env_type in ['dev','prod'] %}
{% set ami = "%s_ami"|format(env_type) %}
{% set located_ami = "%s_located_ami"|format(env_type) %}
{% if ami == located_ami %}
... do stuff
{% else %}
... do other stuff
{% endif %}
{% endfor %}

I have checked through various filters and so far have had no success. Would appreciate advice on getting this specific implementation to work properly. Thank you in advance.

Answer 1

I think you might be approaching the problem with the wrong datastructure in mind.

Dynamically generating variable names in order to compare amis in different environemts sounds like a massive overkill to me. Are you familiar with lists & dictionaries?

Try to start from something like this (pseudocode):

dict = { environments:
            prod:
               ami1: foo
               ami1_located: foo
            dev:
               ami1: bar
               ami1_located:baz
}

for env in dict[environments]:
   if env[ami1] == env[ami1_located]:
      [...]