Idempotent

According to Wikipedia, 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 (https://en.wikipedia.org/wiki/Idempotence). In more common terms, it means that running the same procedure over and over again does not change the system after the first time. Ansible aims to be idempotent, which is good for network operations that require a certain order of operations.

The advantage of idempotence is best compared to the Pexpect and Paramiko scripts that we have written. Remember that these scripts were written to push out commands as if an engineer was sitting at the terminal. If you were to execute the script 10 times, the script will make changes 10 times. If we write the same task via the Ansible playbook, the existing device configuration will be checked first, and the playbook will only execute if the changes do not exist. If we execute the playbook 10 times, the change will only be applied during the first run, with the next 9 runs suppressing the configuration change. 

Being idempotent means we can repeatedly execute the playbook without worrying that there will be unnecessary changes made. This is important as we need to automatically check for state consistency without any extra overhead.