Explain mutable vs. immutable infrastructure

In mutable infrastructure paradigm, changes are applied on top of the existing infrastructure and over time the infrastructure builds up a history of changes. Ansible, Puppet and Chef are examples of tools which follow mutable infrastructure paradigm.

In immutable infrastructure paradigm, every change is actually a new infrastructure. So a change to a server will result in a new server instead of updating it. Terraform is an example of technology which follows the immutable infrastructure paradigm.