ansible.builtin.assert Module: Validate Variables & Conditions (Guide)
By Luca Berton · Published 2024-01-01 · Category: troubleshooting
How to use Ansible assert module (ansible.builtin.assert) to validate variables, check conditions, and fail gracefully. Practical YAML examples with that, fail_msg, success_msg parameters.
Introduction
The assert module in Ansible is a powerful tool for validating conditions and ensuring the correctness of your automation workflows. By halting execution when a condition isn't met, it prevents cascading failures and provides valuable feedback to the user. In this article, we'll explore the quiet, fail_msg, and success_msg parameters, which enhance the flexibility and usability of assertions in playbooks.
What is the assert Module?
The assert module evaluates one or more conditions and ensures they are true. If any condition fails, the module raises an error and stops execution. It's particularly useful for debugging, validation, and ensuring preconditions in complex playbooks.
Basic Syntax
If some_variable doesn't equal expected_value, the playbook will fail at this step.
Enhancing Assertions with quiet, fail_msg, and success_msg
1. quiet: Suppress Output for Passed Assertions
By default, the assert module outputs all evaluated conditions. However, in scenarios where you only want feedback on failures, quiet: true suppresses success messages.
Example:
Use Case: • Keeps playbook output clean and focused, especially when numerous assertions are involved.
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2. fail_msg: Custom Error Messages for Failures
The fail_msg parameter allows you to define a custom error message displayed when the assertion fails. This is invaluable for providing context or instructions for resolving issues.
Example:
Output on Failure:
Use Case: • Improves debugging by clarifying the cause of failure and suggesting corrective actions.
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3. success_msg: Provide Feedback on Success
The success_msg parameter lets you display a custom message when the assertion passes. This is useful for confirming critical preconditions or providing reassurance to the user.
Example:
Output on Success:
Use Case: • Provides positive feedback during playbook execution, boosting confidence in critical tasks.
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Combining All Parameters: A Comprehensive Example
Here's how to use quiet, fail_msg, and success_msg together in a real-world scenario:
Output on Success:
Output on Failure:
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Conclusion
The assert module is an essential tool for creating robust and reliable playbooks. By leveraging quiet, fail_msg, and success_msg, you can tailor its behavior to provide clear, actionable feedback, keeping your automation workflows efficient and user-friendly. Incorporate these features into your playbooks to streamline validation and debugging.
For more tips and real-world examples, explore my book Ansible by Example or check out additional resources below.
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Category: troubleshooting