How to Create a Dynamic Variable in Jinja2 Using Keys from Another Variable

Learn how to dynamically construct variable names in Jinja2 templates based on the value of other variables, specifically for use in Ansible roles.
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Dynamically Building Variable Names in Jinja2 for Ansible

When working with Ansible roles, you might find yourself in a situation where you need to access a variable dynamically based on another variable’s value. This is particularly relevant when you have multiple related variables and want to simplify your template. In this guide, we'll address a common issue and provide a detailed solution for constructing dynamic variable names in Jinja2 templates.

The Problem: Accessing Dynamic Variables in Jinja2

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In your Jinja2 template, you can easily refer to the abc_secret_key using the syntax:

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This works perfectly fine. However, if you're aiming to dynamically build the key name using the customer variable, like so:

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You'll encounter an error message like this:

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This indicates that the dynamic construction of the variable name isn’t working as intended.

The Solution: Using Jinja2 String Concatenation

To resolve this issue, you can employ Jinja2's string concatenation methods to dynamically create the variable name. Here's how you can do it:

Using the ~ Operator

In Jinja2, the ~ operator is used for string concatenation. This allows you to combine different strings seamlessly. Here’s how you can modify your template:

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Example Explained

item[...]: This uses the concatenated string as a dynamic key to access the corresponding secret key.

Using the + Operator

If you're confident that both sides of the concatenation are strings, you can also use the + operator, which works similarly:

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This will produce the same intended result but is less flexible since it assumes both pieces are already of string type.

Conclusion

By utilizing Jinja2's string concatenation capabilities, you can dynamically build variable names based on other variables. This method simplifies your templates and allows for more flexible code organization within your Ansible roles.

Now, you should be able to render outputs like:

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This approach not only solves your immediate problem but also enhances your scripting skills by allowing for more dynamic templates in Jinja2. Keep experimenting with these techniques, and soon you’ll be able to tackle other similar challenges in your scripting endeavors!