What is Terraform? A Comprehensive Guide to Infrastructure as Code

As a full-stack developer, you‘re likely well-versed in writing code to build applications. But have you considered extending those coding skills to your infrastructure as well? That‘s where Terraform comes in.

Terraform is an incredibly powerful tool that enables you to manage your cloud infrastructure using code, a practice known as Infrastructure as Code (IaC). With Terraform, you can define your desired infrastructure state declaratively and let the tool figure out how to make it happen.

In this post, we‘ll take an in-depth look at what Terraform is, how it works, and why it has become an essential tool for many companies and developers. By the end, you‘ll have a solid understanding of the core concepts and workflows, empowering you to start managing infrastructure the same way you build applications. Let‘s dive in!

What is Infrastructure as Code?

Before we get into the specifics of Terraform, it‘s important to understand the concept of Infrastructure as Code that underlies it. Traditionally, setting up infrastructure like servers, databases, and networks involved a lot of manual, time-consuming work. System administrators would need to carefully configure each component by hand.

Infrastructure as Code changes this paradigm. Instead of manually setting up your infrastructure, you represent it through code in configuration files. This code defines the desired end state you want your infrastructure to be in. Tools like Terraform then take those configuration files and make the necessary API calls to cloud providers to provision and configure the specified resources.

The advantages of the IaC approach are significant:

• Automation – Since everything is defined in code, the whole provisioning process can be automated, saving tons of time and reducing the risk of human errors.
• Reusability – Need to set up the same infrastructure in multiple places? No problem, just use the same configuration code.
• Version control – You can store your IaC configuration files in version control systems like Git, enabling collaboration and keeping a full history of changes.
• Consistency – By representing your infrastructure as code, you ensure it‘s provisioned the same way every time, avoiding configuration drift.

With IaC, your infrastructure becomes just like any other code – version controlled, tested, and repeatable. For companies increasingly relying on the cloud to quickly deliver applications, Infrastructure as Code is a necessity, not an option. And Terraform is one of the most popular and powerful IaC tools available.

In fact, according to the State of DevOps 2020 report by Puppet, teams that extensively use IaC tools like Terraform deploy 137x more frequently, have 68x shorter lead times, and recover 2604x faster from incidents compared to low performers [1]. The benefits are clear.

How Terraform Works

At its core, Terraform is an open source command line tool that takes in configuration files defining your desired infrastructure state, then makes API calls to one or more cloud providers to provision and configure those resources.

Terraform configuration files are written in Hashicorp Configuration Language (HCL), a human-readable language specifically designed for defining infrastructure. Here‘s a simple example of what an HCL configuration file might look like to define a virtual machine:

resource "azurerm_virtual_machine" "web_server" {
  name                = "web-server"
  resource_group_name = azurerm_resource_group.example.name
  location            = "eastus"
  vm_size             = "Standard_DS1_v2"

  os_profile {
    computer_name  = "web-server"
    admin_username = "admin"
  }

  os_profile_linux_config {
    disable_password_authentication = true
    ssh_keys {
      key_data = file("~/.ssh/id_rsa.pub")
      path     = "/home/admin/.ssh/authorized_keys"
    }
  }
}

This configuration snippet defines an Azure virtual machine resource with specified attributes like the VM name, size, and SSH authentication settings. Notice how it doesn‘t tell Terraform the specific steps to create the VM, but rather declares the end state that‘s desired. This declarative syntax is a key feature of Terraform – you define what you want, and let Terraform figure out how to make it happen.

Under the hood, when you run terraform apply, Terraform goes through several steps:

1. Refresh – Terraform queries infrastructure provider APIs to get the current state of any already-existing resources defined in the configuration.
2. Plan – Terraform compares the current infrastructure state to the desired state defined in the configuration. It determines what actions (create, update, delete) are needed to make the current state match the desired state.
3. Apply – After getting confirmation from the user, Terraform makes the API calls to the infrastructure provider to carry out the planned changes.

This process is possible because of Terraform‘s plugin-based architecture. For each infrastructure provider (AWS, Azure, Google Cloud, etc.), there‘s a provider plugin that knows how to talk to that provider‘s APIs. Terraform Core itself contains the logic for the refresh-plan-apply cycle. The separation of Terraform Core from provider plugins is a key reason for Terraform‘s flexibility and extensibility.

After applying changes, Terraform saves the updated state of the infrastructure in a state file. This state file acts as the single source of truth for the managed infrastructure. Terraform uses it to determine what changes to make in subsequent runs. It‘s a critical component that enables Terraform‘s declarative model and idempotency (the ability to apply the same configuration multiple times without different results).

Terraform vs Other IaC Tools

Terraform isn‘t the only Infrastructure as Code tool out there. Other popular options include:

• CloudFormation – AWS‘s native IaC tool. It uses YAML or JSON templates to define and provision AWS resources.
• Azure Resource Manager (ARM) templates – Azure‘s native IaC solution. Like CloudFormation, it uses JSON templates.
• Google Cloud Deployment Manager – Google Cloud‘s IaC tool, which uses YAML configuration files.
• Pulumi – An open source IaC tool that allows you to define infrastructure using familiar programming languages like JavaScript, TypeScript, Python, and Go.

So why choose Terraform over these other options? Here are a few key reasons:

• Cloud agnosticism – Terraform supports over 100 different providers, including all the major cloud platforms. You can manage resources across multiple clouds using the same tool and syntax.
• State management – Terraform‘s state management is more robust than many other tools. The state file can be stored remotely, enabling collaboration and reducing the risk of state file corruption.
• Ecosystem – Terraform has a large and active community. There are countless community-created modules available for common infrastructure setups, and many tools integrate with Terraform.
• Flexibility – Because Terraform is provider-agnostic and extensible, it can be used to manage a wide variety of infrastructure, not just cloud resources. Providers exist for databases, monitoring systems, version control systems, and more.

That said, Terraform isn‘t always the best choice. If you‘re working exclusively with a single cloud provider, that provider‘s native tool (like CloudFormation for AWS) may be simpler to use. And for very complex infrastructure, tools like Pulumi that allow using full programming languages can be more powerful.

But for most use cases, especially multi-cloud setups, Terraform is an excellent choice. Its versatility, strong state management, and active ecosystem make it a go-to for many teams.

Terraform Best Practices and Pitfalls

As with any tool, there are right and wrong ways to use Terraform. Here are some best practices to follow:

• Use modules – As your infrastructure grows, your Terraform configuration can become unwieldy. Break it into smaller, reusable modules to keep it manageable.
• Pin provider versions – Specify exact versions for your provider plugins to ensure your configuration always works as expected.
• Use a remote backend for state – Storing state remotely (in S3, Azure Storage, etc.) promotes collaboration and reduces the risk of state file corruption.
• Leverage workspaces – Terraform workspaces allow managing multiple environments (dev, staging, prod) with the same configuration.
• Validate and format your code – Use terraform validate and terraform fmt to catch errors and ensure consistent formatting.

Some common pitfalls to avoid:

• Not using a remote state backend – Local state files are fine for solo development, but problematic for teams.
• Not pinning provider versions – Unplanned provider updates can break your configuration.
• Over-using provisioners – Terraform provisioners are useful for simple setup tasks, but for complex configuration management, use a dedicated tool like Ansible.
• Not using a .gitignore file – You don‘t want to commit .terraform directories or terraform.tfstate files to version control.

Terraform in the DevOps Lifecycle

Terraform isn‘t just a standalone tool – it‘s a key component of many DevOps workflows. In a typical setup:

1. Developers write application code and define the infrastructure needed to run it using Terraform configuration.
2. Version control systems like Git store the application code and Terraform configuration together.
3. Continuous integration pipelines (using tools like Jenkins, CircleCI, etc.) validate the Terraform configuration and application code whenever changes are pushed.
4. Continuous deployment pipelines automatically apply the Terraform configuration to provision and update infrastructure.

This setup enables infrastructure to be versioned and updated in lockstep with the application code that depends on it. Infrastructure becomes a first-class citizen in the development process, not an afterthought.

The Future of Terraform and IaC

As more and more companies adopt cloud and DevOps practices, the importance of Infrastructure as Code will only continue to grow. And Terraform is well-positioned to remain a leader in the IaC space.

One exciting development is the growing ecosystem around Terraform. Tools like Atlantis (for Terraform pull request automation), Terragrunt (for keeping Terraform DRY), and Terraform Validator (for enforcing best practices) are making Terraform even more powerful and user-friendly.

Another trend is the rise of multi-cloud and hybrid cloud setups. As companies look to avoid vendor lock-in and leverage the best of each cloud platform, tools like Terraform that can manage resources across clouds will be increasingly essential.

Terraform is also expanding beyond its roots in infrastructure provisioning. With providers for services like Datadog, Fastly, and Cloudflare, Terraform can now manage application and network configuration too. This broadens Terraform‘s appeal and makes it a versatile tool for many aspects of DevOps.

Of course, Terraform isn‘t without competition. Tools like Pulumi and AWS CDK, which allow defining infrastructure using general-purpose programming languages, are gaining popularity. And each cloud provider continues to invest in their own native IaC solutions.

But given its wide adoption, robust feature set, and active community, Terraform is likely to remain a go-to choice for infrastructure management for the foreseeable future. As a developer or DevOps engineer, learning Terraform is a smart investment.

Conclusion

In a world where infrastructure is increasingly defined by code, Terraform is an indispensable tool. Its declarative approach, combined with its support for multiple providers and robust state management, make it a powerful choice for provisioning and managing resources.

But Terraform isn‘t just a tool – it represents a shift in how we think about infrastructure. By treating infrastructure as code, we can apply the same practices we use in software development. We can version control our infrastructure, collaborate on changes, and automate provisioning.

Whether you‘re a developer looking to expand your skillset or a system administrator seeking to modernize your workflow, learning Terraform is a valuable investment. With its growing popularity and active community, Terraform skills are in high demand.

Of course, this post has only scratched the surface of what Terraform can do. As you start using it more, you‘ll discover features like workspaces for managing multiple environments, Terraform Cloud for remote execution and collaboration, and a huge ecosystem of community modules.

So what are you waiting for? Install Terraform, spin up some resources, and start managing your infrastructure as code today. Trust me, once you experience the power and convenience of Terraform, you won‘t want to go back to the old manual ways.

Happy provisioning!

References

[1] 2020 State of DevOps Report, Puppet, 2020, https://puppet.com/resources/report/2020-state-of-devops-report/