Ansible pre_tasks: Streamlining Automation with Pre-Execution Actions
In the world of IT automation, Ansible stands out as a powerful, open-source tool that simplifies the management and configuration of complex systems. Among its many features, pre_tasks play a crucial role in ensuring that essential steps are executed before the main automation tasks. In this blog, we will explore the importance of Ansible pre_tasks, their use cases, and how they enhance automation workflows.

What Are pre_tasks in Ansible?
pre_tasks in Ansible are special tasks that run before the main tasks in a playbook. They allow you to execute actions that must be completed prior to the main sequence of operations, such as setting up system environments, validating conditions, or ensuring certain prerequisites are met.

A playbook in Ansible is typically divided into multiple sections, such as:

pre_tasks: Tasks that run before the main playbook tasks.
tasks: The main set of instructions or commands that automate system management or configuration.
post_tasks: Actions that run after the main tasks have completed.
Why Use pre_tasks?
There are several reasons why pre_tasks are critical in automation workflows:

Environment Preparation: Before deploying software or making configurations, certain environments may need to be set up. pre_tasks ensure that all the necessary prerequisites, like installing specific packages or ensuring a service is running, are completed first.
Validation and Checks: Before executing the primary tasks, you may want to validate system conditions or configurations. For instance, checking whether a certain package or software version is already installed or whether the operating system version meets the required criteria.
Error Handling: If a system fails to meet certain conditions, pre_tasks can prevent the playbook from proceeding by issuing a fail or warning message. This ensures that the playbook doesn't execute actions that may lead to unexpected results due to unmet prerequisites.
Condition-Based Execution: Sometimes, certain tasks only need to be executed under specific conditions. With pre_tasks, you can conditionally control the flow of your playbook by running checks before the main tasks begin.
Example of Using pre_tasks in a Playbook
Here’s a basic example of a playbook that uses pre_tasks to check the operating system type before continuing with the main tasks:

yaml

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• name: Example Playbook with pre_tasks hosts: all become: true pre_tasks:
  • name: Ensure the system is running Ubuntu ansible.builtin.assert: that: "ansible_facts['distribution'] == 'Ubuntu'" fail_msg: "This playbook only runs on Ubuntu!" success_msg: "System is Ubuntu, proceeding with the playbook." tasks:
  • name: Update package manager apt: update_cache: yes
  • name: Install Apache Web Server apt: name: apache2 state: present In this example:

The pre_tasks section checks whether the target system is running Ubuntu by using the ansible_facts['distribution']. If the condition is not met, the playbook will stop execution and display a failure message.
If the condition is met, the main tasks are executed, which include updating the package manager and installing Apache.
Use Cases for pre_tasks
Here are some practical scenarios where pre_tasks can enhance your Ansible automation:

Package Installation Verification: You may want to verify whether certain packages are installed before proceeding with a software deployment. Using pre_tasks, you can conditionally install these packages if they aren’t already present.
Environment Variable Setup: Sometimes, certain environment variables need to be configured before a set of tasks can run. pre_tasks can handle this setup so that the subsequent tasks have access to the necessary environment settings.
User Validation: When deploying sensitive changes or configurations, you might want to ensure that the correct user is executing the playbook. With pre_tasks, you can check the current user and enforce user-specific conditions before proceeding.
Conditional Execution Based on System State: For certain tasks, the system’s state (such as available memory, disk space, or CPU load) may dictate whether it’s safe to proceed. pre_tasks can gather facts and perform validations before the main tasks execute.
Best Practices for Using pre_tasks
While pre_tasks are a powerful feature, they should be used wisely to enhance automation efficiency. Here are some best practices:

Keep pre_tasks Short and Focused: Use pre_tasks only for critical validations and environment setup. Avoid placing too many complex operations in pre_tasks, as this could make troubleshooting difficult.
Use Conditions Where Necessary: Apply conditional logic (when statements) in pre_tasks to ensure that they only run when needed. This prevents unnecessary operations and speeds up playbook execution.
Handle Errors Gracefully: When using pre_tasks, handle failure scenarios carefully by providing clear error messages or using ignore_errors and failed_when clauses to avoid disrupting workflows unnecessarily.
Document pre_tasks Clearly: Since pre_tasks are often critical to the success of the main tasks, ensure they are well-documented. Describe why each pre_task is necessary to help other team members understand its purpose.

Conclusion

Ansible pre_tasks provide an effective way to ensure that your automation workflows run smoothly by taking care of pre-execution checks, environment setup, and condition-based validation. By incorporating pre_tasks into your playbooks, you can increase reliability, prevent issues, and create more streamlined and maintainable automation processes.

Whether you’re setting up infrastructure, deploying applications, or configuring complex environments, pre_tasks can be a key feature in making your Ansible workflows more robust and efficient.

Ready to level up your automation processes with Ansible? Check out more guides and tutorials at Cloudastra Technologies, or contact us for tailored automation solutions!