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Discover how to dynamically generate templates in Ansible based on valid IP addresses, avoiding unnecessary configurations.
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How to Check for Valid IP Addresses in Ansible with Jinja2 Templates

When working with Ansible, one common task is to generate configurations based on certain criteria. In this case, we’re tackling the challenge of checking if a list of host addresses contains valid IPs. If valid IPs are found, we want to generate a template for firewall rules; if not, we skip the generation. Let’s explore how to solve this problem effectively using Ansible's powerful templating features and its built-in testing capabilities.

The Problem: Dynamic Template Generation Based on IP Validity

Imagine you have a list of allowed hosts with their respective IP addresses, and you need to enforce firewall rules based on these addresses. The key here is that we only want to generate rules for hosts if there are valid IP addresses present. If there are no valid addresses, we shouldn't generate the corresponding templates for the firewall rules.

Sample Variables

You might have variables defined like this:

[[See Video to Reveal this Text or Code Snippet]]

In this scenario, my_allowed_hosts2 contains addresses that we want to validate before proceeding with template generation.

The Solution: Leveraging Jinja2 Templating

To implement the logic for checking valid IP addresses and conditionally generating templates, we will follow these steps:

Step 1: Validate IP Addresses

We will use Ansible’s built-in filter options to extract and validate the addresses from my_allowed_hosts2. Specifically, we will employ the json_query filter along with ipaddr for validation:

[[See Video to Reveal this Text or Code Snippet]]

This step essentially populates valid_addresses with a list of addresses that pass the validation, filtering out loopback addresses.

Step 2: Generate Templates Conditionally

Next, we need to ensure that we create the templates only for valid groups. We can use a loop combined with conditions in the when clause:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Logic

Conditional Looping: The when clause checks:

If the item is in our my_ferm_groups

Whether firewall_whitelist2 should be included based on whether valid_addresses is non-empty.

This means if there are valid IP addresses detected, both firewall_whitelist1 and firewall_whitelist2 could generate configurations. If not, firewall_whitelist2 will be skipped.

Example Usage

Here are two scenarios to demonstrate the solution:

No Matching IPs:
When valid_addresses is empty, only firewall_whitelist1 would get processed.

[[See Video to Reveal this Text or Code Snippet]]

One or More Matching IPs:
In this case, both firewall_whitelist1 and firewall_whitelist2 would yield configurations.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By following this approach, you establish a clear and organized mechanism to validate IP addresses and conditionally generate firewall templates in Ansible tasks. This not only ensures efficiency but also keeps your configurations tidy and relevant to the current state of your environment.

Final Notes

Always validate your models and variables to ensure that they are structured correctly before running your Ansible playbooks.

Utilize Ansible's debugging features to troubleshoot and ensure that your logic flows correctly.

By placing emphasis on the power of Jinja2 templating and conditional logic, you can effectively manage your network configurations with precision.