Custom Terraform Module Development for Infrastructure

Imagine three teams in a company writing Terraform code for similar infrastructure, each with their own templates. Different VPC versions, different EKS cluster configurations, different security group rules. When an update to best practices for EBS encryption comes out, you have to update three independent codebases. This not only slows down deployments but multiplies errors: encryption is enabled in one environment but not in another. We help standardize this process with reusable Terraform modules. Order turnkey module development—and forget about code duplication and manual fixes.

Why Terraform modules save up to 40% time

A well-designed module is more than just a folder with code. It is a standard building block that can be safely reused across all environments: dev, staging, prod. Instead of copying code, you call the module with environment parameters. Our experience shows this approach reduces VPC deployment time from two hours to five minutes—a 24x improvement. Overall infrastructure deployment time drops by up to 40%, and the number of errors falls by 40%. In monetary terms, this saves up to $4,000 per month on a single project.

How to distinguish a good module from a bad one

A bad module is a monster with 50+ required variables. A good module has a minimal required interface and sensible defaults. For example, an RDS instance requires only identifier, engine_version, instance_class, and subnet_ids. Everything else—backup_retention_period, deletion_protection, performance_insights_enabled—has safe defaults that can be overridden. Compare:

Why testing Terraform modules is critical

Without tests, changes to a module can silently break infrastructure. Terratest is a Go library for integration tests. The test deploys the module in a real cloud, verifies required resources are created, and destroys everything afterward. This is expensive (time + cloud costs), but indispensable for critical modules. Learn more about Terratest in the official repository.

func TestRDSModule(t *testing.T) {
    opts := &terraform.Options{
        TerraformDir: "../examples/basic",
        Vars: map[string]interface{}{
            "identifier": "test-db",
        },
    }
    defer terraform.Destroy(t, opts)
    terraform.InitAndApply(t, opts)
    endpoint := terraform.Output(t, opts, "endpoint")
    assert.NotEmpty(t, endpoint)
}

For quick syntax and basic pattern checks—terraform validate and tflint with a set of rules for the specific provider. In CI, this takes seconds.

How we build the module hierarchy

Typically, we start with a base set: VPC, compute (EC2/ECS), managed database (RDS), load balancer, and object storage (S3). These modules cover 80% of a typical project's needs. Building more complex modules on top—like an EKS module that internally uses node-group, IRSA, and addon modules—becomes straightforward. This hierarchy speeds up deployment by 3x compared to copying code.

How we design the module structure

We follow a standard structure:

modules/rds-postgres/
  main.tf          # resources
  variables.tf     # input variables with description and default
  outputs.tf       # what we expose
  versions.tf      # required_providers with version constraints
  README.md        # generated automatically by terraform-docs

versions.tf is mandatory. We specify the minimum Terraform version and provider versions. As stated in the official Terraform documentation, version constraints prevent incompatibility during upgrades. Read more about required_providers in the Terraform documentation.

terraform {
  required_version = ">= 1.5.0"
  required_providers {
    aws = {
      source = "hashicorp/aws"
      version = ">= 5.0, < 6.0"
    }
  }
}

Without this, the module could break when Terraform is updated in CI without a clear warning. Large modules are often built from smaller ones. The eks-cluster module internally calls node-group, irsa, and addons modules. This is fine—but only if nesting does not exceed 2–3 levels. Deeper than that, terraform plan becomes unpredictable in execution time, and the dependency graph becomes unreadable. For public modules (Terraform Registry), adhering to the standard structure (modules/, examples/, test/) is mandatory. For internal modules in a Git monorepo, the structure is more flexible, but examples/ should still be maintained—it serves as living documentation.

What is included in the work?

1. Audit of current infrastructure and requirements—identifying bottlenecks and module goals.
2. Module architecture design—defining interfaces, hierarchy, versioning.
3. Development of a base set of modules—VPC, compute, managed database, load balancer, object storage.
4. Writing integration tests (Terratest)—for critical modules.
5. Documentation generation—README via terraform-docs, examples in examples/.
6. Publication and handover—repository access, team training.
7. Post-release support—bug fixes and consultations for one month.

Timelines and experience

Developing a base set of modules for one provider takes 2–4 weeks. Complex services (EKS with add-ons, hybrid networks) require a separate assessment. We guarantee code quality and documentation: our engineers are certified (AWS Certified DevOps Engineer, HashiCorp Certified: Terraform Associate) and have years of experience in infrastructure automation, with over 40 successful projects. Contact us to assess your tasks—we will prepare a proposal for module development tailored to your infrastructure. Get a consultation.