What Puppet function can ensure a resource is managed only once?

The Puppet function that ensures a resource is managed only once is the "ensure" function. In Puppet manifests, the "ensure" attribute is commonly used to define the desired state of a resource. For example, it can be used to indicate whether a resource should be present or absent. When the "ensure" function is applied to a resource, it effectively guarantees that Puppet will take action only if the resource is not already in the desired state, thus ensuring that the resource is managed only once.

By using the "ensure" function with values such as 'present' or 'absent', Puppet manages the resource’s lifecycle appropriately. If a resource is already present and "ensure" is set to 'present', Puppet will not attempt to recreate it, thereby managing the resource once and avoiding unnecessary actions. This behavior makes "ensure" fundamental for idempotent resource management, which is a core principle of configuration management in Puppet.

The other options provided do not represent valid Puppet functions for managing resource states. "Unique," "absolutely," and "one_time" do not correspond to any recognized functions or attributes within Puppet's resource management paradigm, which is why they do not serve the intended purpose of ensuring a resource is managed only once.