Ansible troubleshooting - Error run-once
How to Solve the Ansible Error run-once
Understanding the Ansible Playbook Error:
When developing Ansible playbooks, it’s crucial to ensure efficient execution and adhere to best practices. This includes using strategies that align with the desired behavior of your tasks and plays. In the world of Ansible, the
run_once directive is a powerful tool. It is used to ensure that a particular task runs only once in a playbook. However, its use can become problematic if not handled correctly, especially when used in conjunction with the
strategy: free configuration.
In Ansible, the
run_once directive allows you to specify that a task should execute only once, regardless of how many hosts are involved in the playbook. This is particularly useful when you have a task that should be performed only on the control node or a single target host, even in a scenario where multiple hosts are being managed.
Here’s a quick example:
- name: Ensure setup is done once hosts: all gather_facts: no tasks: - name: Perform setup ansible.builtin.debug: msg: "This setup should run once" run_once: true
In this example, the
debug task will execute only once, even if it’s part of a playbook applied to multiple hosts.
Ansible Lint Output
WARNING Listing 2 violation(s) that are fatal yaml[truthy]: Truthy value should be one of [false, true] run_once.yml:4 run-once[task]: Using run_once may behave differently if strategy is set to free. run_once.yml:6 Task/Handler: Perform setup Read documentation for instructions on how to ignore specific rule violations. Rule Violation Summary count tag profile rule associated tags 1 yaml[truthy] basic formatting, yaml 1 run-once[task] idiom Failed: 2 failure(s), 0 warning(s) on 1 files. Last profile that met the validation criteria was 'min'.
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The Issue with
One common pitfall occurs when you use the
run_once directive in combination with the
strategy: free setting. The
strategy: free tells Ansible to parallelize tasks as much as possible, which can lead to unexpected results when used with
run_once. This combination may not guarantee that the task runs only once due to the parallel nature of
To prevent this misalignment of strategies, Ansible Lint has a rule called
run-once. This rule checks if the
run_once directive is used when the playbook’s strategy is set to
free. If it encounters this scenario, it issues a warning to prompt the user to reconsider their strategy choices.
Proper Usage and Resolutions
To ensure that your playbook works as expected, consider the following best practices:
run_once: If your playbook includes tasks with the
run_oncedirective, it’s a good practice to avoid using
strategy: freefor that specific playbook. A playbook-level
strategy: freecan be overridden by the command line, which may lead to unexpected results.
- name: "Example of using run_once with a strategy other than free" hosts: all strategy: linear gather_facts: false tasks: - name: Task with run_once ansible.builtin.debug: msg: "Test" run_once: true
Disable the Rule: If you have a specific reason to use
strategy: free, you can disable the
run-oncerule for the task where you intentionally need this combination by adding
# noqa: run-once[task]as a comment in your playbook.
- name: "Example with run_once" hosts: all strategy: free gather_facts: false tasks: - name: Task with run_once ansible.builtin.debug: msg: "Test" run_once: true # noqa: run-once[task]
By following these best practices and understanding how
strategy: free interact, you can create more predictable and efficient Ansible playbooks. This ensures that your automation tasks run as intended, regardless of the complexity of your infrastructure.
Note: Always consider the specific requirements of your infrastructure and choose the strategy that aligns with your desired behavior.
Remember, in the world of Ansible, clarity and predictability are keys to success in managing and automating your IT environment.
In conclusion, when working with Ansible playbooks, it’s essential to ensure that the chosen strategies align with the intended behavior of tasks and plays. The use of the
run_once directive, a powerful tool to execute a task only once, must be carefully handled, especially when combined with the
strategy: free configuration. The
run-once rule in Ansible Lint serves as a valuable reminder and best practice guideline, helping users avoid potential issues with the use of
run_once under the
strategy: free scenario.
Proper playbook design and strategy selection are crucial for achieving predictable and efficient automation tasks. While
run_once offers fine-grained control over task execution, a mismatch with
strategy: free can lead to unintended results due to parallelization. By following the best practices outlined in this article, you can create reliable and maintainable Ansible playbooks.
Always prioritize the clarity and predictability of your automation tasks to effectively manage and automate your IT environment. Carefully consider the specific requirements of your infrastructure and choose the strategy that best fits your needs. In doing so, you can maximize the effectiveness of your Ansible playbooks while minimizing potential issues and unexpected behavior.Subscribe to the YouTube channel, Medium, Website, Twitter, and Substack to not miss the next episode of the Ansible Pilot.
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