The AzureRM Terraform provider is one of the most actively maintained cloud providers in the Terraform ecosystem. The patterns for building reusable, maintainable infrastructure modules have matured alongside it.
Module composition patterns
Terraform modules should have a single, clear responsibility. A module for an AKS cluster encapsulates the node pool configuration, identity setup, monitoring integration, and network configuration. A module for an Azure SQL database encapsulates the server, database, firewall rules, and diagnostic settings. Composing these modules in a top-level configuration builds the complete environment from components that can be tested independently.
Variable validation
Terraform's variable validation block lets you define constraints that are checked before the plan runs. For a module that accepts a VM SKU variable, a validation that checks the SKU is in the set of approved sizes catches misconfiguration before it reaches Azure. Variable descriptions and validation provide the documentation and constraint checking that makes a module usable without reading its implementation.
Testing with Terratest
Terratest is a Go library for testing Terraform configurations. A Terratest test provisions real infrastructure, runs assertions against it, and destroys it. The tests are slow (infrastructure provisioning takes minutes) and cost money (real resources are created). The value is proportional to the reuse: a module used across 20 environments is worth the investment in automated testing that verifies it works correctly after changes.
The CI/CD pipeline for infrastructure
A Terraform CI/CD pipeline: a PR triggers terraform plan, the plan output is posted as a comment on the PR for review, merge triggers terraform apply against the target environment, and the state file is stored in Azure Blob Storage with locking. Sentinel policies (Terraform Enterprise) or custom scripting (Open Policy Agent) can enforce constraints on the plan before apply is permitted.