Infrastructure as Code with Terraform

Terraform

Terraform is an infrastructure as code tool that lets you build, change, and version cloud and on-prem resources safely and efficiently. HashiCorp Terraform is an infrastructure as code tool that lets you define both cloud and on-prem resources in human-readable configuration files that you can version, reuse, and share. You can then use a consistent workflow to provision and manage all of your infrastructure throughout its lifecycle. (developer.hashicorp.com)

How it’s used:

Write HashiCorp Configuration Language (HCL) files to declare providers and resources.
Run terraform init to initialize the directory and install provider plugins. (developer.hashicorp.com)
Run terraform plan to preview changes Terraform will make. (developer.hashicorp.com)
Run terraform apply to enact the plan, creating, updating, or destroying resources. (developer.hashicorp.com)
Manage state (terraform.tfstate), optionally using remote backends for collaboration and locking.

Example Usage

GNS3 Official Installation Guides

In order to get the real gist of network automation always have containerlab, cisco packet tracer and gns3 with some cisco router template or any router installed. The following link will help you setup gns3 on your local machine

General Getting Started & Installation Overview https://docs.gns3.com/docs/getting-started/installation
Windows Installation https://docs.gns3.com/docs/getting-started/installation/windows/
macOS Installation https://docs.gns3.com/docs/getting-started/installation/mac/
Ubuntu/Linux Installation https://docs.gns3.com/docs/getting-started/installation/linux/
Remote Server Installation https://docs.gns3.com/docs/getting-started/installation/remote-server/
GNS3 VM Setup Wizard https://docs.gns3.com/docs/getting-started/setup-wizard-gns3-vm/

Terraform Provider for GNS3

Overview
The Terraform Provider for GNS3 enables you to manage your GNS3 network emulation topologies as code. With this provider, you can create projects, instantiate routers, switches, clouds, and links entirely via Terraform—bringing the benefits of Infrastructure as Code (IaC) to your lab and testing environments. :contentReference[oaicite:0]{index=0}

Key Features

Project Management: Create and configure GNS3 projects (gns3_project).
Node Resources: Instantiate and manage routers, switches, and cloud nodes directly from templates (gns3_template, gns3_switch, gns3_cloud).
Link Automation: Define network links between nodes declaratively (gns3_link).
Lifecycle Actions: Start or stop all nodes within a project (gns3_start_all). :contentReference[oaicite:1]{index=1}

Today we will be deploying a cisco (c7200) router on gns3 using template resource. Create main.tf in a new Directory.

terraform {
  required_providers {
    gns3 = {
      source  = "netopschic/gns3"
      version = "2.4.0"
    }
  }
}

provider "gns3" {
  host = "http://localhost:3080"
}

# Lookup the Cisco 7200 template ID
data "gns3_template_id" "router" {
  name = "c7200"
}

# Create a GNS3 Project
resource "gns3_project" "project1" {
  name = "cisco-topology"
}

# Instantiate three routers from the template
resource "gns3_template" "r1" {
  name        = "R1"
  project_id  = gns3_project.project1.project_id
  template_id = data.gns3_template_id.router.template_id
  compute_id  = "local"
  x           = -200
  y           = -100
}

resource "gns3_template" "r2" {
  name        = "R2"
  project_id  = gns3_project.project1.project_id
  template_id = data.gns3_template_id.router.template_id
  compute_id  = "local"
  x           =  200
  y           = -100
}

resource "gns3_template" "r3" {
  name        = "R3"
  project_id  = gns3_project.project1.project_id
  template_id = data.gns3_template_id.router.template_id
  compute_id  = "local"
  x           =    0
  y           =  200
}

# Link each router to each other (full mesh)
resource "gns3_link" "r1_r2" {
  project_id     = gns3_project.project1.project_id
  node_a_id      = gns3_template.r1.id
  node_a_adapter = 1
  node_a_port    = 0
  node_b_id      = gns3_template.r2.id
  node_b_adapter = 1
  node_b_port    = 0
}

resource "gns3_link" "r2_r3" {
  project_id     = gns3_project.project1.project_id
  node_a_id      = gns3_template.r2.id
  node_a_adapter = 1
  node_a_port    = 0
  node_b_id      = gns3_template.r3.id
  node_b_adapter = 1
  node_b_port    = 0
}

resource "gns3_link" "r3_r1" {
  project_id     = gns3_project.project1.project_id
  node_a_id      = gns3_template.r3.id
  node_a_adapter = 1
  node_a_port    = 0
  node_b_id      = gns3_template.r1.id
  node_b_adapter = 1
  node_b_port    = 0
}

# Start all three routers once they are created
resource "gns3_start_all" "start_routers" {
  project_id = gns3_project.project1.project_id
  depends_on = [
    gns3_template.r1,
    gns3_template.r2,
    gns3_template.r3,
  ]
}

terraform init

Terraform Workflow: init → plan → apply

Terraform follows a simple three-step workflow to take your HCL configuration files and turn them into real infrastructure:

1. `terraform init`

What it does:

Initializes your working directory for Terraform.
Downloads and installs provider plugins declared in required_providers.
Sets up the backend for state storage (local file or remote).
Retrieves any modules you’ve referenced.

When to run:

First time in a new directory.
After adding or changing providers or modules.

Example:

cd my-terraform-project/
terraform init

Key output:

“Initializing the backend…”
“Initializing provider plugins…”
Summary of installed plugins and backend details.

2. `terraform plan`

What it does:

Reads current state (terraform.tfstate or remote).
Queries real infrastructure to refresh state.
Compares your HCL with actual state to calculate changes.
Outputs a plan showing resources to create (+), modify (~), or destroy (-).

When to run:

Before applying changes, to verify desired outcome.

Example:

terraform plan \
  -out=changes.tfplan

data.gns3_template_id.router: Reading...
data.gns3_template_id.router: Read complete after 0s [id=6dc0dd4c-aec2-4818-98a8-3b12a4410119]

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following
symbols:
  + create

Terraform will perform the following actions:

  # gns3_link.r1_r2 will be created
  + resource "gns3_link" "r1_r2" {
      + id             = (known after apply)
      + link_id        = (known after apply)
      + node_a_adapter = 1
      + node_a_id      = (known after apply)
      + node_a_port    = 0
      + node_b_adapter = 1
      + node_b_id      = (known after apply)
      + node_b_port    = 0
      + project_id     = (known after apply)
    }

  # gns3_link.r2_r3 will be created
  + resource "gns3_link" "r2_r3" {
      + id             = (known after apply)
      + link_id        = (known after apply)
      + node_a_adapter = 1
      + node_a_id      = (known after apply)
      + node_a_port    = 0
      + node_b_adapter = 1
      + node_b_id      = (known after apply)
      + node_b_port    = 0
      + project_id     = (known after apply)
    }

  # gns3_link.r3_r1 will be created
  + resource "gns3_link" "r3_r1" {
      + id             = (known after apply)
      + link_id        = (known after apply)
      + node_a_adapter = 1
      + node_a_id      = (known after apply)
      + node_a_port    = 0
      + node_b_adapter = 1
      + node_b_id      = (known after apply)
      + node_b_port    = 0
      + project_id     = (known after apply)
    }

  # gns3_project.project1 will be created
  + resource "gns3_project" "project1" {
      + id         = (known after apply)
      + name       = "cisco-topology"
      + project_id = (known after apply)
    }

  # gns3_start_all.start_routers will be created
  + resource "gns3_start_all" "start_routers" {
      + id         = (known after apply)
      + project_id = (known after apply)
    }

  # gns3_template.r1 will be created
  + resource "gns3_template" "r1" {
      + compute_id  = "local"
      + id          = (known after apply)
      + name        = "R1"
      + project_id  = (known after apply)
      + start       = false
      + template_id = "6dc0dd4c-aec2-4818-98a8-3b12a4410119"
      + x           = -200
      + y           = -100
    }

  # gns3_template.r2 will be created
  + resource "gns3_template" "r2" {
      + compute_id  = "local"
      + id          = (known after apply)
      + name        = "R2"
      + project_id  = (known after apply)
      + start       = false
      + template_id = "6dc0dd4c-aec2-4818-98a8-3b12a4410119"
      + x           = 200
      + y           = -100
    }

  # gns3_template.r3 will be created
  + resource "gns3_template" "r3" {
      + compute_id  = "local"
      + id          = (known after apply)
      + name        = "R3"
      + project_id  = (known after apply)
      + start       = false
      + template_id = "6dc0dd4c-aec2-4818-98a8-3b12a4410119"
      + x           = 0
      + y           = 200
    }

Plan: 8 to add, 0 to change, 0 to destroy.

Key output:

“Terraform will perform the following actions:”
A color-coded list of resource actions.
A summary: “Plan: 3 to add, 1 to change, 0 to destroy.”

3. `terraform apply`

What it does:

Takes an execution plan (new or saved).
Prompts for confirmation (optional: -auto-approve).
Provisions, updates, or tears down resources in dependency order.

When to run:

After reviewing and approving your plan.

Examples:

# Apply fresh plan in-memory
terraform apply

gns3_project.project1: Creating...
gns3_project.project1: Creation complete after 0s [id=11a4dd9c-9b52-4341-9355-4f8e789c224e]
gns3_template.r1: Creating...
gns3_template.r3: Creating...
gns3_template.r2: Creating...
gns3_template.r3: Creation complete after 0s [id=a2e6ea15-8c15-49c7-b63d-f086716f3318]
gns3_template.r2: Creation complete after 0s [id=2fc90300-d2e3-4ab7-9934-0d0b938712d8]
gns3_link.r2_r3: Creating...
gns3_template.r1: Creation complete after 0s [id=1f0c71dd-96ed-459b-b1de-996de5dc9050]
gns3_start_all.start_routers: Creating...
gns3_link.r3_r1: Creating...
gns3_link.r1_r2: Creating...
gns3_start_all.start_routers: Creation complete after 1s [id=11a4dd9c-9b52-4341-9355-4f8e789c224e-start]
gns3_link.r1_r2: Creation complete after 1s [id=04e36dee-a571-474f-816c-6d59ce51d1f8]
gns3_link.r3_r1: Creation complete after 1s [id=f03d6a5c-51a3-41a5-90d1-14335e3c1340]
gns3_link.r2_r3: Creation complete after 1s [id=8f0ca331-e663-492d-b8ac-4cefdf3d154c]

Apply complete! Resources: 8 added, 0 changed, 0 destroyed

Key output:

Progress logs for each resource action.
Final summary: “Apply complete! Resources: +3 added, ~1 changed, -0 destroyed.”

Challenge

Create an EC2 instance using terraform
Create an s3 bucket using terraform

References

Official Terraform Documentation: https://developer.hashicorp.com/terraform/intro
Official OpenTofu Website: https://opentofu.org/

GitHub Repository: https://github.com/NetOpsChic/terraform-provider-gns3

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Infrastructure as Code with Terraform

Terraform

Example Usage

GNS3 Official Installation Guides

Terraform Provider for GNS3

Key Features

Terraform Workflow: init → plan → apply

1. `terraform init`

2. `terraform plan`

3. `terraform apply`

Challenge

References

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Infrastructure as Code with Terraform

Terraform

Example Usage

GNS3 Official Installation Guides

Terraform Provider for GNS3

Key Features

Terraform Workflow: init → plan → apply

1. terraform init

2. terraform plan

3. terraform apply

Challenge

References

1. `terraform init`

2. `terraform plan`

3. `terraform apply`