Ansible development is fast, and anyone using Ansible extensively has most likely come across an instance where a playbook that used to work does not work on a later Ansible version. Or, a system that wasn’t supported initially is now added and an existing role requires modification to make it work on the new system. See Molecule for Ansible role creation for more details on using and debugging Molecule. Creating a Molecule scenario to test an existing role allows for easy testing and modification of that role with all the benefits that Molecule provides.
In our Quality Engineering organization, we create, configure, and destroy a lot of servers via automation. Ansible is a great method for handling the configuration of servers, but the creation of Ansible roles and playbooks can be trial and error for even experienced Operations Engineers. Molecule provides a way to speed up the development and confidence of Ansible roles and playbooks by wrapping a virtualization driver with tools for testing and linting.
Handling a huge scale of infrastructure requires automation and infrastructure as code. Terraform is a tool that helps to manage a wide variety of systems including dynamic server lifecycle, configuration of source code repositories, databases, and even monitoring services. Terraform uses text configuration files to define the desired state of infrastructure. From those files, Terraform provides information on the changes to be made based on the current state of that infrastructure, and can make those changes.