Infrastructure as Code (IaC)

Infrastructure as Code (IaC): Terraform vs Pulumi for Managing Cloud Infrastructure Declaratively and Reproducibly

If you’re a developer or a cloud enthusiast, chances are you’ve heard of Infrastructure as Code (IaC). It’s one of those game-changing concepts that has transformed how we build, deploy, and maintain cloud infrastructure. Instead of manually clicking around in cloud consoles or writing long bash scripts, IaC lets you define your infrastructure in code — making it repeatable, version-controlled, and collaborative.

In this post, we’ll dive into two popular IaC tools: Terraform and Pulumi. We’ll explore how they help you manage your cloud infrastructure declaratively and reproducibly, compare their philosophies, and even walk through some practical examples. By the end, you’ll have a clearer picture of which tool might fit your projects best and how to get started with them.

What is Infrastructure as Code (IaC)?

Before we jump into tools, let’s make sure we’re on the same page.

Infrastructure as Code means managing and provisioning computing infrastructure through machine-readable configuration files, rather than physical hardware configuration or interactive configuration tools.

Think of it like this:

  • Instead of clicking around in the AWS Console to create a VM, you write a config file declaring what you want.
  • Instead of manually SSH’ing into servers and installing software, you automate it through code.
  • Your infrastructure setup becomes repeatable, version-controlled, and less error-prone.

IaC empowers teams to treat infrastructure just like application code — with reviews, testing, and continuous integration.

Declarative vs Imperative IaC: Why Declarative Wins for Cloud Infrastructure

There are two broad approaches to IaC:

  • Imperative: You write step-by-step instructions (e.g., create VM, install software, configure network).
  • Declarative: You declare the desired state of your infrastructure, and the tool figures out how to get there.

Most modern IaC tools, including Terraform and Pulumi, lean heavily on the declarative side. Why? Because it’s easier to reason about what you want rather than how to get it.

Imagine telling a tool: “I want 3 web servers behind a load balancer, with this security group.” The IaC tool handles the actual provisioning, updates, and teardown.

Meet Terraform and Pulumi: Two Approaches to Declarative IaC

Terraform: The Industry Stalwart

Terraform is probably the most widely used IaC tool out there. It was created by HashiCorp and has become the de facto standard for cloud infrastructure automation.

  • Language: HashiCorp Configuration Language (HCL) — a simple, domain-specific language designed for infrastructure.
  • Providers: Terraform supports hundreds of providers (AWS, Azure, GCP, Kubernetes, and many more).
  • State management: It keeps track of your infrastructure state in a file (local or remote), which allows it to know what changes to make.
  • Community: Huge community, tons of modules, and solid documentation.

With Terraform, you write .tf files declaring resources like VPCs, EC2 instances, databases, etc. You run terraform apply and it creates or updates your infrastructure to match your config.

Pulumi: The Developer-Friendly Alternative

Pulumi is a newer player in the IaC space but with an interesting twist:

  • Language: Use familiar programming languages like JavaScript/TypeScript, Python, Go, or C#.
  • Flexibility: You can leverage existing language features (loops, functions, abstractions, libraries).
  • Providers: Supports all major cloud providers and Kubernetes.
  • State management: Like Terraform, Pulumi manages state automatically; you can also store it remotely.

Pulumi targets developers who want to use their existing language skills rather than learning a new DSL. It also makes complex infrastructure logic easier to express.

Declaratively Managing Cloud Infrastructure: Terraform vs Pulumi in Action

Let’s look at how both tools handle a simple scenario: provisioning an AWS S3 bucket.

Terraform Example: Creating an S3 Bucket

Here’s a minimal Terraform config for an S3 bucket:

provider "aws" {
  region = "us-west-2"
}

resource "aws_s3_bucket" "my_bucket" {
  bucket = "my-unique-bucket-terraform-2024"
  acl    = "private"
}

To deploy:

terraform init      # Initialize Terraform and download providers
terraform plan      # See what changes will be made
terraform apply     # Apply the changes (create the bucket)

Terraform figures out if the bucket exists, creates it if not, and stores the state in a local file (or remote backend).

Pulumi Example: Creating an S3 Bucket in TypeScript

Here’s how you’d do the same with Pulumi (TypeScript):

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

const bucket = new aws.s3.Bucket("myBucket", {
    bucket: "my-unique-bucket-pulumi-2024",
    acl: "private",
});

Deploy it with:

pulumi login          # Login to Pulumi service or set up local backend
pulumi stack init     # Create a new stack (environment)
pulumi up             # Preview and apply changes

Pulumi tracks the state in its service or locally and manages updates automatically.

Key Differences Between Terraform and Pulumi

AspectTerraformPulumi
LanguageHashiCorp Configuration Language (HCL)General-purpose languages (TS, Python, Go, C#)
Learning CurveEasy to pick up for simple configs, but HCL can be limiting for complex logicUses familiar languages, so easier for developers comfortable with those
Modularity & ReuseSupports modules and templatesLeverages functions, classes, and packages naturally
State ManagementLocal files or remote backends (S3, Consul, etc.)Pulumi service or local files
CommunityLarge, mature, lots of modulesGrowing, less mature but active and innovative
Execution ModelPlan & apply: Terraform plans changes, then appliesPulumi previews changes and applies in one command
Complex LogicLimited, relies on workarounds (count, for_each)Full programming power to build abstractions
Multi-language supportN/ASupports multiple languages out of the box

When to Choose Terraform?

  • You prefer a declarative DSL that’s purpose-built for infrastructure.
  • Your team or existing infrastructure already uses Terraform.
  • You want access to a huge ecosystem of community modules.
  • You prefer explicit plans and a mature, battle-tested tool.
  • You don’t want to manage or learn another language’s dependencies.

Terraform works great for most traditional infrastructure use cases and is an excellent starting point.

When to Choose Pulumi?

  • You are a developer or team comfortable with TypeScript, Python, Go, or C#.
  • You want to write complex infrastructure logic with loops, functions, or packages.
  • You want to integrate infrastructure code tightly with application code.
  • You like the idea of using one language across your stack.
  • You want to try a modern IaC tool with some unique features like rich SDKs and preview UIs.

Pulumi shines in scenarios where infrastructure logic is complex or highly dynamic.

Practical Example: Creating an AWS EC2 Instance with Terraform and Pulumi

Let’s step it up a notch. Suppose you want to create an EC2 instance with a security group.

Terraform

provider "aws" {
  region = "us-west-2"
}

resource "aws_security_group" "web_sg" {
  name        = "web-sg"
  description = "Allow HTTP inbound traffic"

  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_instance" "web" {
  ami           = "ami-0c55b159cbfafe1f0" # Amazon Linux 2 AMI (example)
  instance_type = "t2.micro"
  security_groups = [aws_security_group.web_sg.name]

  tags = {
    Name = "TerraformWebServer"
  }
}

Run terraform init, terraform plan, and terraform apply to create the security group and EC2 instance.

Pulumi (TypeScript)

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

const webSg = new aws.ec2.SecurityGroup("webSg", {
    description: "Allow HTTP inbound traffic",
    ingress: [{
        protocol: "tcp",
        fromPort: 80,
        toPort: 80,
        cidrBlocks: ["0.0.0.0/0"],
    }],
    egress: [{
        protocol: "-1",
        fromPort: 0,
        toPort: 0,
        cidrBlocks: ["0.0.0.0/0"],
    }],
});

const webServer = new aws.ec2.Instance("webServer", {
    ami: "ami-0c55b159cbfafe1f0", // Amazon Linux 2 AMI
    instanceType: "t2.micro",
    securityGroups: [webSg.name],
    tags: {
        Name: "PulumiWebServer",
    },
});

Run pulumi up to preview and create the resources.

How Both Tools Enable Reproducibility and Collaboration

One of IaC’s biggest wins is reproducibility. You can spin up the exact same infrastructure in multiple environments — dev, staging, production — with confidence.

Both Terraform and Pulumi:

  • Use state files to track infrastructure.
  • Support remote backends for team collaboration.
  • Integrate with CI/CD pipelines to automate deployments.
  • Allow storing code in version control (Git) for change history and code reviews.

This means your infrastructure changes become safer and more auditable.

Tips for Getting Started

  1. Pick one tool and stick with it initially — jumping between tools can be confusing.
  2. Start small — begin with a simple resource (like an S3 bucket) and grow your config.
  3. Use remote state management early — it avoids headaches when working in teams.
  4. Write clear, modular code — use modules (Terraform) or functions/classes (Pulumi) to keep configs organized.
  5. Leverage community modules/providers — they save tons of time.
  6. Test your infrastructure changes — use tools like terraform plan, Pulumi previews, or testing frameworks.

Summary: Terraform vs Pulumi for Declarative, Reproducible Cloud Infrastructure

Infrastructure as Code is a powerful practice that empowers teams to manage cloud infrastructure as software — making provisioning declarative, reproducible, and collaborative.

  • Terraform is a mature, widely adopted tool with its own configuration language (HCL). It’s battle-tested, has a rich ecosystem, and works well for most infrastructure use cases.
  • Pulumi brings a fresh take by letting you use familiar programming languages to define infrastructure. It’s great for developers who want to leverage programming constructs and integrate infrastructure more tightly with application code.

At the end of the day, both tools help you declare your desired cloud infrastructure state and manage it reproducibly. Your choice depends on your team’s skills, the complexity of your infrastructure, and your personal preferences.

Whichever you choose, embracing IaC will make your infrastructure more reliable, scalable, and maintainable — and that’s a win for every developer and operations team.

Ready to try it out? Spin up your first S3 bucket with Terraform or Pulumi today and see how infrastructure as code can simplify your cloud workflows! 🚀