Infrastructure as Code is the practice of defining infrastructure deployments using machine-readable files that can be used to provision infrastructure in an automated fashion.

Terraform is an example of Infrastructure-as-Code (IaC), and therefore HashiCorp expects that you have a fundamental understanding of what IaC is and some of its concepts and patterns. This exam objective is not focused specifically around Terraform itself but covers general topics of Infrastructure-as-Code.

Infrastructure can be thought of as the resources an application runs on. Traditionally this was composed of servers, storage, and networking. With the advent of virtualization, servers were now split into both physical resources and virtual machines. Cloud providers created additional abstractions, starting with Infrastructure-as-a-Service (IaaS) and moving up to Platform-as-a- Service (PaaS) and Software-as-a-Service (SaaS). While traditional infrastructure was deployed using manual and cumbersome processes fraught with potential for mistakes and inconsistencies, the various services offered by cloud providers and other vendors introduce a software-driven model of creation and configuration.

Infrastructure-as-Code (IaC) is the practice of defining and provisioning infrastructure resources through a machine-readable format. The infrastructure provisioned and managed using IaC can include bare-metal servers, virtual machines, networking resources, storage volumes, or even databases provided as a service. While IaC is often used in a cloud environment, it is not necessary to use the cloud for IaC. As long as your infrastructure management system has a programmatic interface, it can participate in IaC.

The format can be declarative (defining the desired outcome) or imperative (defining the process of provisioning.) Declarative provisioning solutions, such as Terraform, are focused on the desired end state of a deployment and rely on an interpretation engine to create and configure the actual resources. Imperative provisioning solutions, such as a batch script, focus on the actual provisioning process and may reference a file containing a list of settings and configuration values. The code created for IaC may be stored in a Version Control System (VCS) to enable change tracking and team collaboration. IaC can also be combined with other common software development practices like automated testing, deployment pipelines, and reusable components.

The key point behind Iac is that infrastructure is defined and provisioned through machine-readable code and is not provisioned by hand using a portal, command line, or API. If the commands or process is performed manually by a person, it is not IaC.

The advantages of using IaC can be broken down into a few key categories: consistency, repeatability, and efficiency.

• By defining infrastructure as code, the deployment of that infrastructure should be consistent across multiple builds and environments. When the same code is used to stand up infrastructure for staging and production, the operations team no longer has to wonder if the two environments are at parity.
• In a cloud context, using the same code to deploy infrastructure in multiple regions assures that each region is set up consistently.
• There are many common components and deployment patterns in infrastructure. Using IaC allows these patterns to be defined once and used multiple times. For example, it may be a common pattern to deploy web servers for a new application. By defining the web server deployment in code, it can be reused by each new deployment that requires a set of web servers. Additionally, if something changes about the desired configuration of those web servers, an update of the web server deployment code can be created and pushed to each application environment.
• Defining infrastructure as code allows operations teams to more tightly integrate with their developer counterparts. The provisioning process of infrastructure can be incorporated into the existing application development workflow, creating a consistent and repeatable process that flows through development, QA, staging, and production environments. By automating and integrating with the development team, greater levels of efficiency can be achieved.