Infrastructure as Code: Terraform vs. Pulumi in Practice

Provisioning cloud infrastructure through web consoles does not scale. Manual setups create drift, lack auditability, and slow teams down as environments grow. Infrastructure as Code (IaC) solves this by treating infrastructure definitions as versioned, testable artifacts. Two tools dominate the IaC space: HashiCorp’s Terraform and Pulumi. Both aim to make infrastructure reproducible, but they take fundamentally different approaches to get there.

This article compares both tools across concrete criteria and provides a decision framework that goes beyond surface-level feature lists.

Language Model: HCL vs. General-Purpose Languages

The most visible difference: Terraform uses its own configuration language, HCL (HashiCorp Configuration Language). Pulumi lets you write infrastructure definitions in TypeScript, Python, Go, or C#.

HCL is declarative by design and intentionally constrained. What looks like a limitation turns out to be a strength in practice: Terraform configurations are readable even for team members without deep programming experience. Operations engineers coming from an infrastructure background pick it up quickly.

resource "aws_s3_bucket" "data_lake" {
  bucket = "company-data-lake-prod"

  tags = {
    Environment = "production"
    ManagedBy   = "terraform"
  }
}

resource "aws_s3_bucket_versioning" "data_lake" {
  bucket = aws_s3_bucket.data_lake.id
  versioning_configuration {
    status = "Enabled"
  }
}

The same infrastructure expressed in Pulumi with TypeScript:

import * as aws from "@pulumi/aws";

const dataLake = new aws.s3.Bucket("data-lake", {
  bucket: "company-data-lake-prod",
  tags: {
    Environment: "production",
    ManagedBy: "pulumi",
  },
});

const versioning = new aws.s3.BucketVersioningV2("data-lake-versioning", {
  bucket: dataLake.id,
  versioningConfiguration: {
    status: "Enabled",
  },
});

Pulumi shines when complex logic enters the picture: loops, conditionals, class-based abstractions, and compile-time type checking. Teams with a software engineering background benefit from this. Teams with a traditional ops background tend to be more productive with HCL.

State Management: Tracking What Exists

Both tools maintain a state file that represents the current state of managed infrastructure. Terraform stores this state locally as JSON by default. For teams, a remote backend is essential, typically S3 with DynamoDB for locking, or Terraform Cloud.

terraform {
  backend "s3" {
    bucket         = "company-tf-state"
    key            = "prod/infrastructure.tfstate"
    region         = "eu-central-1"
    dynamodb_table = "terraform-locks"
    encrypt        = true
  }
}

Pulumi provides a managed service (app.pulumi.com) as the default backend, handling state storage, locking, and encryption out of the box. Alternatively, state can be stored in S3, Azure Blob, or locally. The managed service works well but introduces a dependency on Pulumi as a vendor.

For regulated environments where data must stay on-premises, Terraform with a self-managed backend is the more established option. Pulumi offers self-hosted backends too, but the ecosystem around that path is less mature.

Testing: Validating Infrastructure Before Deployment

This is where Pulumi has a conceptual advantage. Since Pulumi programs are regular code files, unit tests use the standard test framework for the chosen language:

import * as pulumi from "@pulumi/pulumi";
import { describe, it, expect } from "vitest";

pulumi.runtime.setMocks({
  newResource: (args) => ({ id: `${args.name}-id`, state: args.inputs }),
  call: () => ({}),
});

describe("S3 Bucket", () => {
  it("should have correct tags", async () => {
    const infra = await import("../index");
    const bucket = infra.dataLake;

    const tags = await new Promise<Record<string, string>>((resolve) =>
      bucket.tags.apply((t) => resolve(t ?? {}))
    );

    expect(tags.ManagedBy).toBe("pulumi");
  });
});

Terraform offers terraform validate and terraform plan for basic checks. For actual testing, Terratest (Go-based) or the newer Terraform Testing Framework with .tftest.hcl files are available. The learning curve is steeper, but the ecosystem of modules and patterns is mature.

Teams already running CI/CD pipelines with test stages will appreciate Pulumi’s native test approach. Teams that rely primarily on code reviews and plan output inspection will find Terraform sufficient.

Multi-Cloud and Provider Ecosystem

Terraform has the clear advantage of scale here: over 4,000 providers in the registry, covering AWS, Azure, GCP, Cloudflare, Datadog, Kubernetes, and nearly every cloud service in existence. Community contributions are extensive, documentation is thorough, and battle-tested patterns exist for most common architectures.

Pulumi also supports all major cloud platforms and can use Terraform providers as bridged providers. In practice, this works well most of the time, though there can be delays for new features or edge-case incompatibilities.

For multi-cloud setups spanning AWS, Azure, and on-premises infrastructure, Terraform is the more proven choice. Not because Pulumi cannot handle it, but because Terraform modules have seen wider production testing across diverse environments.

Modules and Reusability

Terraform uses modules as its abstraction mechanism. A module is a directory of .tf files parameterized through variables. The Terraform Registry contains thousands of ready-made modules for VPC setups, EKS clusters, RDS instances, and more.

Pulumi uses Component Resources, which are classes that bundle multiple resources. Since these are real code, they can be distributed through npm, PyPI, or other package managers:

class ProductionVpc extends pulumi.ComponentResource {
  public readonly vpcId: pulumi.Output<string>;

  constructor(name: string, args: VpcArgs, opts?: pulumi.ComponentResourceOptions) {
    super("company:network:Vpc", name, {}, opts);

    const vpc = new aws.ec2.Vpc(`${name}-vpc`, {
      cidrBlock: args.cidr,
      tags: { Name: name, ManagedBy: "pulumi" },
    }, { parent: this });

    this.vpcId = vpc.id;
    this.registerOutputs({ vpcId: this.vpcId });
  }
}

Both approaches work. Terraform’s module system is simpler and better documented. Pulumi’s class-based approach is more powerful but demands software engineering discipline to keep abstractions manageable.

Decision Guide: When to Choose Which

The choice between Terraform and Pulumi is not about one being objectively better. It depends on team context and requirements.

Terraform is the right choice when the team consists primarily of operations engineers, the organization manages a large multi-cloud setup, or Terraform modules and workflows are already established. The massive community, mature registry, and broad tooling support (Atlantis, Spacelift, env0) make it the safe default.

Pulumi is the better fit when the infrastructure team has a strong software engineering background, testing and type safety for infrastructure code are priorities, or infrastructure is tightly coupled with application code. In TypeScript-heavy environments where backend, frontend, and infrastructure share the same language, Pulumi reduces context switching significantly.

For mid-sized companies (the German “Mittelstand” and similar SMBs across Europe) just starting with IaC, Terraform is often the more pragmatic entry point. The learning curve is flatter, documentation is more extensive, and experienced Terraform practitioners are easier to find in the job market. Pulumi becomes compelling as the team grows and requirements around testability and abstraction increase.

Conclusion

Infrastructure as Code is no longer optional for teams managing cloud environments at scale. Terraform remains the de facto standard with the broadest ecosystem. Pulumi offers a more modern developer experience, especially for teams that want to treat infrastructure like application code.

Both tools solve the same problem. The decision comes down to who will work with the tool daily and what the existing toolchain looks like. When in doubt, run a small proof of concept with both and let real experience guide the decision rather than theoretical feature comparisons.

At EverBright IT, we help cloud teams select and implement IaC tools, from initial strategy to production-ready pipelines. Learn more about our cloud services or get in touch →

Frequently Asked Questions

What is Infrastructure as Code?

Infrastructure as Code treats infrastructure definitions as versioned, testable code artifacts instead of manual console configuration. Infrastructure is defined in files, stored in version control, reviewed in pull requests, and deployed through automated pipelines. This approach eliminates drift, improves auditability, and enables teams to reproduce environments reliably.

Should I choose Terraform or Pulumi?

Choose Terraform if your team is operations-focused, you manage multi-cloud setups, or Terraform is already established. It has broader ecosystem support and easier onboarding for infrastructure specialists. Choose Pulumi if your team has strong software engineering skills, testing and type safety matter, or infrastructure is tightly coupled with application code. TypeScript-heavy teams benefit from shared language.

What does a Terraform state file do?

The state file tracks the current state of managed infrastructure. It maps resource names in code to actual cloud resources and stores resource attributes. Terraform compares desired state (code) to actual state (file) to determine what changes to apply. For teams, state must be stored remotely with locking (S3 plus DynamoDB) to prevent concurrent modifications and conflicts.

Can Pulumi use Terraform providers?

Yes, Pulumi can bridge Terraform providers, allowing access to over 4,000 cloud and service providers. This works well for most use cases but can have delays for new features or edge-case incompatibilities. For multi-cloud or specialized infrastructure needs, Terraform has more battle-tested providers and broader community support.

How do I test infrastructure code?

Terraform offers terraform validate and terraform plan for basic checks. Terratest (Go-based) or newer Terraform Testing Framework (.tftest.hcl) enable proper testing. Pulumi, being real code, uses standard language test frameworks. Unit tests mock resources, integration tests verify actual behavior. Teams without test discipline find planning and code review sufficient initially.