Introduction

In the realm of Terraform, the terraform plan command is the architect's desk where you blueprint and preview your infrastructure changes before, they are applied. This guide unfolds the layers of terraform plan, dissecting the processes that occur during its execution. An example scenario will guide us through the planning journey, revealing the power of foresight in your Terraform orchestrations.

1. Terraform Plan: The Architect's Preview

When you're ready to transform your infrastructure with Terraform, the terraform plan command provides you with a detailed preview of the changes it will apply. It's a crucial step in your infrastructure-as-code workflow, offering insight into the additions, modifications, or deletions Terraform will enact.

2. Example Scenario: AWS EC2 Instance Modification

Let's embark on an example scenario where we modify an existing AWS EC2 instance configuration using Terraform. The focus is on the planning process and the insightful information terraform plan provides.

2.1. Configuration Breakdown:

# main.tf

provider "aws" {
  region = "us-east-1"
}

resource "aws_instance" "example_instance" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
}

2.2. Modification: Scaling Up the Instance Type

We'll modify the configuration to scale up the instance type to a more robust t2.small.

# main.tf (modified)

provider "aws" {
  region = "us-east-1"
}

resource "aws_instance" "example_instance" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.small"
}

3. Planning Process: What Happens?

Executing terraform plan initiates a comprehensive process, giving you a crystal-clear preview of the impending changes:

3.1. Configuration Parsing:

• Terraform parses your configuration files, understanding the defined resources, providers, and their interdependencies.

3.2. Resource Analysis:

• Terraform analyzes the modifications, additions, or deletions to resources, providing an insightful breakdown.

3.3. Dependency Graph Construction:

• A dependency graph is constructed, depicting the relationships between resources and their dependencies.

3.4. Execution Plan Generation:

• Terraform generates an execution plan, outlining the sequence of operations to be performed to achieve the desired state.

3.5. Output:

• The terraform plan command presents a detailed output, showcasing the proposed changes, resource actions, and any potential issues or conflicts.

4. Applying the Command:

To preview the changes, execute the following command:

terraform plan

5. Output of the Command:

Here's a hypothetical output of the terraform plan command for our scenario:

Terraform will perform the following actions:

  # aws_instance.example_instance will be updated in-place
  ~ resource "aws_instance" "example_instance" {
        ami           = "ami-0c55b159cbfafe1f0"
        instance_type = "t2.small" # (forces new resource replacement)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

6. Conclusion: Previewing the Terraform Symphony

terraform plan is the symphony conductor of your Terraform orchestra, orchestrating a detailed preview of changes before they resonate in your infrastructure. By providing foresight into modifications, additions, or deletions, this command ensures that you have full control and understanding of the orchestration that is about to unfold.

May your Terraform planning be insightful, empowering you to architect and envision your infrastructure changes with clarity and confidence! 🎶🏗️