First Look - Terraform HCL vs Pulumi Programs

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Let’s try creating the same resources using both Terraform HCL and a Pulumi program. This basic example will also serve to verify your cloud connectivity.

The Terraform way of doing things

In Terraform, if you wanted to query an AMI ID you might write something like this in Hashicorp Configuration Language (HCL):

data "aws_ami" "ubuntu" {
  region      = "us-west-2"
  most_recent = true
  owners      = ["099720109477"] # Canonical

  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"]
  }
}

output "latest_ubuntu_ami_id" {
  value = data.aws_ami.ubuntu.id
}

output "latest_ubuntu_ami_name" {
  value = data.aws_ami.ubuntu.name
}

If you run this Terraform config, you should see output showing the latest Ubuntu AMI information. However, it’s important to note that HCL is not a programming language. It is a configuration language, similar to YAML or JSON, with a bit more expressiveness and modularization capabilities. In Pulumi, you use general purpose programming languages to express your desired state of your cloud resources, in the context of a Pulumi program.

Pulumi programs

Let’s try creating the same resources in a Pulumi program. The key difference between Terraform and Pulumi is that Pulumi allows you to use your preferred programming language instead of HCL. Both approaches query the same AWS API and return identical results:

First, create a new Pulumi program:

$ mkdir pulumi-terraform-test && cd pulumi-terraform-test
$ pulumi new aws-typescript --yes

Replace the contents of index.ts with:

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

// Query existing Ubuntu AMIs (read-only operation)
const ubuntu = aws.ec2.getAmiOutput({
    region: "us-west-2",
    mostRecent: true,
    owners: ["099720109477"], // Canonical
    filters: [
        {
            name: "name",
            values: ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"],
        },
    ],
});

export const latestUbuntuAmiId = ubuntu.id;
export const latestUbuntuAmiName = ubuntu.name;

First, create a new Pulumi program:

$ mkdir pulumi-terraform-test && cd pulumi-terraform-test
$ pulumi new aws-python --yes

Replace the contents of __main__.py with:

import pulumi
import pulumi_aws as aws

# Query existing Ubuntu AMIs (read-only operation)
ubuntu = aws.ec2.get_ami(
    region="us-west-2",
    most_recent=True,
    owners=["099720109477"],  # Canonical
    filters=[
        {
            "name": "name",
            "values": ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"],
        }
    ],
)

pulumi.export("latestUbuntuAmiId", ubuntu.id)
pulumi.export("latestUbuntuAmiName", ubuntu.name)

First, create a new Pulumi program:

$ mkdir pulumi-terraform-test && cd pulumi-terraform-test
$ pulumi new aws-go --yes

Replace the contents of main.go with:

package main

import (
	"github.com/pulumi/pulumi-aws/sdk/v7/go/aws/ec2"
	"github.com/pulumi/pulumi/sdk/v3/go/pulumi"
)

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {
		// Query existing Ubuntu AMIs (read-only operation)
		ubuntu, err := ec2.LookupAmi(ctx, &ec2.LookupAmiArgs{
            Region: pulumi.StringRef("us-west-2"),
			MostRecent: pulumi.BoolRef(true),
			Owners:     []string{"099720109477"}, // Canonical
			Filters: []ec2.GetAmiFilter{
				{
					Name:   "name",
					Values: []string{"ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"},
				},
			},
		})
		if err != nil {
			return err
		}

		ctx.Export("latestUbuntuAmiId", pulumi.String(ubuntu.Id))
		ctx.Export("latestUbuntuAmiName", pulumi.String(ubuntu.Name))
		return nil
	})
}

First, create a new Pulumi program:

$ mkdir pulumi-terraform-test && cd pulumi-terraform-test
$ pulumi new aws-csharp --yes

Replace the contents of Program.cs with:

using System.Collections.Generic;
using Pulumi;
using Pulumi.Aws.Ec2;
using Pulumi.Aws.Ec2.Inputs;

return await Deployment.RunAsync(() =>
{
    // Query existing Ubuntu AMIs (read-only operation)
    var ubuntu = GetAmi.Invoke(new()
    {
        Region = "us-west-2",
        MostRecent = true,
        Owners = new[] { "099720109477" }, // Canonical
        Filters = new[]
        {
            new GetAmiFilterInputArgs
            {
                Name = "name",
                Values = new[] { "ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*" },
            },
        },
    });

    return new Dictionary<string, object?>
    {
        ["latestUbuntuAmiId"] = ubuntu.Apply(ubuntu => ubuntu.Id),
        ["latestUbuntuAmiName"] = ubuntu.Apply(ubuntu => ubuntu.Name),
    };
});

First, create a new Pulumi program:

$ mkdir pulumi-terraform-test && cd pulumi-terraform-test
$ pulumi new aws-java --yes

Replace the contents of src/main/java/myproject/App.java with:

package myproject;

import com.pulumi.Pulumi;
import com.pulumi.aws.ec2.Ec2Functions;
import com.pulumi.aws.ec2.inputs.GetAmiArgs;
import com.pulumi.aws.ec2.inputs.GetAmiFilterArgs;
import com.pulumi.core.Output;

import java.util.List;

public class App {
    public static void main(String[] args) {
        Pulumi.run(ctx -> {
            // Query existing Ubuntu AMIs (read-only operation)
            var ubuntu = Ec2Functions.getAmi(GetAmiArgs.builder()
                .region("us-west-2")
                .mostRecent(true)
                .owners("099720109477") // Canonical
                .filters(GetAmiFilterArgs.builder()
                    .name("name")
                    .values("ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*")
                    .build())
                .build());

            ctx.export("latestUbuntuAmiId", ubuntu.applyValue(ami -> ami.id()));
            ctx.export("latestUbuntuAmiName", ubuntu.applyValue(ami -> ami.name()));
        });
    }
}

First, create a new Pulumi program:

$ mkdir pulumi-terraform-test && cd pulumi-terraform-test
$ pulumi new aws-yaml --yes

Replace the contents of Pulumi.yaml with:

name: pulumi-terraform-test
runtime: yaml
description: Test Pulumi and AWS connectivity

variables:
  ubuntu:
    fn::invoke:
      function: aws:ec2:getAmi
      arguments:
        region: us-west-2
        mostRecent: true
        owners: ["099720109477"] # Canonical
        filters:
          - name: name
            values: ["ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"]

outputs:
  latestUbuntuAmiId: ${ubuntu.id}
  latestUbuntuAmiName: ${ubuntu.name}

Run the test:

$ pulumi up

You should see output showing the latest Ubuntu AMI information, confirming that Pulumi can successfully query your AWS environment.

Clean up

Remove the test resources:

$ pulumi destroy --yes
$ pulumi stack rm --yes
$ cd .. && rm -rf pulumi-terraform-test

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