Contents
Why is Ansible idempotent?
When a playbook is executed to configure a system, the system should always have the same, well defined state. By its nature, Ansible tasks will only change the system if there is something to do. Most Ansible modules provide this idempotency.
Are Ansible modules idempotent?
The principle that enables Ansible to be declarative and yet reliable is idempotence, a concept borrowed from mathematics. An idempotent operation is one that can be applied multiple times without changing the result beyond the initial application, such as multiplication by zero. Ansible modules are idempotent.
What do you mean by idempotent?
In computing, an idempotent operation is one that has no additional effect if it is called more than once with the same input parameters. For example, removing an item from a set can be considered an idempotent operation on the set. In mathematics, an idempotent operation is one where f(f(x)) = f(x).
What is idempotent playbook?
For Ansible it means after 1 run of a playbook to set things to a desired state, further runs of the same playbook should result in 0 changes. In simplest terms, idempotency means you can be sure of a consistent state in your environment.
What are modules in Ansible?
A module is a reusable, standalone script that Ansible runs on your behalf, either locally or remotely. Modules interact with your local machine, an API, or a remote system to perform specific tasks like changing a database password or spinning up a cloud instance.
What is Idempotent property?
Idempotence is a property that an operation in mathematics or computer science may have. It roughly means that the operation can be carried out again and again without changing the result. The word idempotence was made by Benjamin Pierce because he saw the concept when studying algebra.
What does it mean to have idempotence in Ansible?
In general, idempotence is “the property of certain operations in mathematics and computer science that can be applied multiple times without changing the result beyond the initial application”. For Ansible it means after 1 run of a playbook to set things to a desired state, further runs of the same playbook should result in 0 changes.
Why do I have a configuration file in Ansible?
To make things worse, the configuration file is a result of extensive collaboration between few other rapidly developed applications: Ansible playbook, Ansible (version changes may cause a subtle changes in space handling, etc), and few other pieces of software.
When to use tests as filters in Ansible?
If you use Twig, this will look familiar: we’re reading a variable and piping it through some search filter, which comes from Jinja. Using tests as filters is deprecated since Ansible v2.5 and will be removed in v2.9, use is %test_name% or is not %test_name% instead where %test_name% might be any test like success, failed, search, etc, for example:
Why do you need a template module in Ansible?
Ansible’s template or copy modules allow you to prepare an entire file upfront which gives you complete control over the file’s contents. So when possible prefer the copy and template module over manipulating with the lineinfile module.