Terraform Best Practices

Terraform is how we build, change, and version our infrastructure safely and efficiently. It allows us to define our cloud resources (like servers, databases, and networks) in human-readable configuration files that we can share, reuse, and manage with version control, just like application code.

Why We Use Terraform

Declarative: Instead of writing step-by-step instructions (imperative), we simply declare the desired state of our infrastructure. Terraform then figures out how to get there.
State Management: Terraform keeps a state file that maps the resources in our configuration to the real-world resources in AWS. This is how it knows what to create, update, or destroy.
Reproducibility: By defining our infrastructure as code, we ensure we can create identical environments for development, staging, and production, reducing “it works on my machine” problems.

Our Project Structure

We organize our Terraform code into reusable modules. A module is a container for multiple resources that are used together. This helps us keep our code DRY (Don’t Repeat Yourself).

A typical module structure might look like this:

/modules/aws-s3-bucket/ ├── main.tf # Main resource definitions ├── variables.tf # Input variables for the module ├── outputs.tf # Output values from the module └── README.md # Documentation for the module

Policy as Code: Enforcing Security Rules

To ensure our infrastructure code is secure before it’s ever applied, we practice Policy as Code (PaC). We use automated tools to scan our Terraform files for common security misconfigurations.

Our primary tool for this is tfsec. It’s integrated into our CI/CD pipeline and runs automatically when you create a pull request. tfsec checks for things like:

S3 buckets that are publicly exposed.
Security groups that allow unrestricted ingress (0.0.0.0/0).
Unencrypted EBS volumes.

If tfsec finds a high-severity issue, it will fail the build, preventing the insecure code from being merged. You can and should also run tfsec locally on your machine for faster feedback.

FinOps: Estimating Costs Before You Apply

As part of our FinOps culture, we are responsible for the cost of the infrastructure we create. Terraform has tools that help us understand the financial impact of our changes before we apply them.

We use infracost to analyze our Terraform code and provide a cost breakdown of the resources. When you create a pull request, infracost will automatically post a comment showing the monthly cost increase or decrease associated with your changes. This is a critical checkpoint to ensure we are making cost-conscious decisions.

Managing State Securely

The Terraform state file is extremely sensitive. It can contain secrets and provides a full map of our infrastructure. For this reason:

We never store state files on our local machines.
Our state is stored remotely in a secure, versioned, and encrypted S3 bucket.
We use DynamoDB for state locking to prevent multiple people from running Terraform at the same time and corrupting the state.