Introduction:
In this comprehensive WordPress blog post, we will explore an efficient approach to setting variables in Ansible using Jinja2 templates. By leveraging the power of the selectattr filter, we’ll streamline your code and enhance your Ansible workflows. With a focus on simplicity and efficiency, we’ll guide you through handling complex conditions and achieving desired outcomes effortlessly. Get ready to optimize your Ansible development process, simplify syntax, and deploy configurations with ease. Let’s embark on a journey that unravels the potential of Ansible and Jinja2 templates, empowering you to revolutionize your configuration management tasks.
The Scenario
Imagine you have an existing Ansible variable called existing_ansible_var, and you want to set a new variable called new_ansible_var based on different conditions. Here’s the logic you want to achieve:
if {{ existing_ansible_var }} == “string1”
new_ansible_var = “a”
else if {{ existing_ansible_var }} == “string2”
new_ansible_var = “b”
<…>
else
new_ansible_var = “”
While you could combine multiple techniques like variable assignment, conditional comparison, and defaulting filters, it may seem like an overcomplicated solution. But fear not! We have a simpler way to accomplish this using Jinja2 templates in Ansible.
Using a Dictionary
To achieve the desired outcome, we can leverage the power of dictionaries in Jinja2. Here’s a concise and elegant solution:
{{ {“string1”: “a”, “string2”: “b”}[existing_ansible_var] | default(“”) }}
In this one-liner, we define a dictionary where the keys are the possible values of existing_ansible_var, and the values are the corresponding values for new_ansible_var. By using the existing_ansible_var as the index of the dictionary, we can retrieve the appropriate value. The default("") filter ensures that if existing_ansible_var doesn’t match any of the keys, the result will be an empty string.
Defining a Variable
If you need to use the new_ansible_var elsewhere in your playbook or template, you can assign it to a variable. Here’s how you can do it:
vars:
myDict:
string1: a
string2: b
new_ansible_var: ‘{{ myDict[existing_ansible_var | default(“this key does not exist in the dict”)] | default(“”) }}’
In this example, we define a dictionary called myDict and set the values for string1 and string2. Then, we assign the value of new_ansible_var using Jinja2 syntax, accessing the dictionary with myDict[existing_ansible_var] . We also include a default value in case existing_ansible_var is not found in the dictionary.
Simplifying Your Ansible Code
Now that you have a clear and concise way to set variables based on conditions in Ansible, you can simplify your code and make it more maintainable. Instead of using multiple set_fact tasks, you can achieve the same result with a single line using the power of Jinja2.
Remember, simplicity is key when it comes to writing clean and efficient Ansible playbooks. By leveraging the features of Jinja2 and using dictionaries, you can streamline your code and achieve the desired outcome with ease.
Case Statement for Setting Var in Ansible/Jinja2
Are you struggling to set variables in Ansible based on different conditions? Look no further! In this article, we will explore a simple and effective solution using Ansible’s Jinja2 templates. By leveraging the power of Jinja2, we can achieve our desired outcome with ease. Let’s dive in and discover the solution you’ve been searching for.
The Scenario
Let’s say you have an existing Ansible variable called existing_ansible_var, and you want to set a new variable called new_ansible_var based on various conditions. Here’s the logic you want to implement:
if {{ existing_ansible_var }} == “string1”
new_ansible_var = “a”
else if {{ existing_ansible_var }} == “string2”
new_ansible_var = “b”
<…>
else
new_ansible_var = “”
While you could use multiple techniques like variable assignment, conditional comparisons, and defaulting filters, there’s a simpler way to achieve the same result.
Ternary Operator
In Ansible’s Jinja2 templates, you can use the ternary operator to set variables based on conditions. The ternary operator has the following syntax:
{{ condition ? true_value : false_value }}
Using this syntax, we can rewrite our case statement as follows:
{% set new_ansible_var = existing_ansible_var == “string1” ? “a” :
existing_ansible_var == “string2” ? “b” :
“” %}
In this code, we first check if existing_ansible_var is equal to “string1”. If true, we assign the value “a” to new_ansible_var. If false, we move to the next condition. We repeat this process for each condition until we reach the default case, where we assign an empty string.
By utilizing the ternary operator, we can achieve the same result as the case statement in a more concise and readable manner.
Simplifying Your Ansible Code
With this solution, you can simplify your Ansible code by using a single set of statements instead of multiple if-else blocks. The ternary operator allows you to handle all the conditions in a clear and efficient way.
Remember to apply this approach wherever you need to set variables based on conditions in your Ansible playbooks. By utilizing Jinja2’s ternary operator, you can streamline your code and make it more maintainable.
Using the selectattr Filter
Ansible provides a powerful filter called selectattr, which allows you to filter a list of objects based on attribute values. By leveraging this filter, we can simplify the case statement logic and achieve our desired outcome. Here’s how:
{% set new_ansible_var = [
{“value”: “a”, “condition”: existing_ansible_var == “string1”},
{“value”: “b”, “condition”: existing_ansible_var == “string2”},
<…>
{“value”: “”, “condition”: true}
] | selectattr(“condition”) | map(attribute=”value”) | first %}
In this solution, we create a list of dictionaries, where each dictionary contains a "value" key and a "condition" key. We define the values for new_ansible_var corresponding to each condition. The last dictionary with a "condition" set to true serves as the default case, where new_ansible_var is assigned an empty string.
The magic happens when we apply the selectattr filter to the list of dictionaries. We filter the list based on the "condition" key, keeping only the dictionaries where the condition is true. Then, we use the map filter to extract the "value" key from the remaining dictionaries. Finally, we use the first filter to select the first value from the filtered list.
This concise solution allows us to handle complex conditions with ease, simplifying our code and making it more manageable.
Simplifying Your Ansible Code
By utilizing the selectattr filter in Jinja2, you can simplify your Ansible code by eliminating the need for multiple if-else statements. This approach provides a cleaner and more efficient way to set variables based on conditions.
Remember to apply this technique wherever you need to handle case statements in your Ansible playbooks. By leveraging the power of Jinja2 and the selectattr filter, you can streamline your code and enhance the maintainability of your Ansible projects.
Conclusion
In this article, we explored a solution for setting variables in Ansible based on conditions using Jinja2 templates and the selectattr filter. By leveraging this powerful filter, we can simplify complex case statement logic and achieve our desired outcome in a concise manner. Now you have the knowledge to handle similar scenarios in your Ansible projects with confidence.
