Drift detection in CI/CD in Terraform - Mini Project: Build & Apply

Drift detection in CI/CD

📖 Scenario: You are managing infrastructure using Terraform. Sometimes, manual changes happen outside Terraform, causing drift between your declared infrastructure and the actual cloud resources.Detecting this drift early in your CI/CD pipeline helps keep your infrastructure consistent and reliable.

🎯 Goal: Build a simple Terraform configuration and a drift detection step that checks for differences between your Terraform state and real infrastructure.You will create a Terraform resource, configure a drift detection command, and output the drift check result.

📋 What You'll Learn

Create a Terraform configuration file with an AWS S3 bucket resource named exactly example_bucket.

Add a Terraform variable called bucket_name with default value my-unique-bucket-12345.

Use the terraform plan command to detect drift in the infrastructure.

Print the output of the drift detection command.

💡 Why This Matters

🌍 Real World

Infrastructure drift can cause unexpected issues in cloud environments. Detecting drift early helps maintain stable and secure infrastructure.

💼 Career

DevOps engineers and cloud engineers use drift detection to ensure infrastructure as code matches the real deployed resources, preventing configuration errors.

1

Create Terraform configuration with an S3 bucket

Create a Terraform file with a resource named aws_s3_bucket.example_bucket that uses the bucket name from a variable called bucket_name. Define the variable bucket_name with default value my-unique-bucket-12345.

Terraform

# Create variable "bucket_name" with default "my-unique-bucket-12345"
# Create resource "aws_s3_bucket.example_bucket" using variable "bucket_name"
# Your code here

Hint

Use variable block to define bucket_name. Use resource "aws_s3_bucket" "example_bucket" to create the bucket resource.

2

Add a Terraform plan command for drift detection

Add a shell command string variable called drift_command that contains the exact command terraform plan -detailed-exitcode to detect drift.

Terraform

variable "bucket_name" {
  default = "my-unique-bucket-12345"
}

resource "aws_s3_bucket" "example_bucket" {
  bucket = var.bucket_name
}

# Define variable drift_command with value "terraform plan -detailed-exitcode"
# Your code here

Hint

Use a variable block to store the shell command string for drift detection.

3

Create a local-exec provisioner to run drift detection

Add a null resource named drift_check with a local-exec provisioner that runs the command stored in the variable drift_command.

Terraform

variable "bucket_name" {
  default = "my-unique-bucket-12345"
}

resource "aws_s3_bucket" "example_bucket" {
  bucket = var.bucket_name
}

variable "drift_command" {
  default = "terraform plan -detailed-exitcode"
}

# Add resource "null_resource" "drift_check" with local-exec provisioner running var.drift_command
# Your code here

Hint

Use null_resource with a local-exec provisioner to run the drift detection command.

4

Print the drift detection result

Add an output named drift_result that shows the result of running the drift_check resource.

Terraform

variable "bucket_name" {
  default = "my-unique-bucket-12345"
}

resource "aws_s3_bucket" "example_bucket" {
  bucket = var.bucket_name
}

variable "drift_command" {
  default = "terraform plan -detailed-exitcode"
}

resource "null_resource" "drift_check" {
  provisioner "local-exec" {
    command = var.drift_command
  }
}

# Add output "drift_result" to show drift_check resource status
# Your code here

Hint

Use an output block with a value string describing the drift detection result.

Practice

1. What is the main purpose of drift detection in a Terraform CI/CD pipeline?

easy

A. To find differences between the Terraform code and the actual infrastructure

B. To speed up the deployment process by skipping validation

C. To automatically delete unused resources without approval

D. To generate documentation for the infrastructure

Solution

1. Step 1: Understand drift detection concept

   Drift detection compares the current real infrastructure state with the Terraform code to find differences.

2. Step 2: Identify the purpose in CI/CD

   In CI/CD, drift detection helps catch unexpected changes before applying new updates.

3. Final Answer:

   To find differences between the Terraform code and the actual infrastructure -> Option A

4. Quick Check:

   Drift detection = find differences [OK]

Hint: Drift detection = spot differences before apply [OK]

Common Mistakes:

• Thinking drift detection speeds deployment
• Assuming it deletes resources automatically
• Confusing it with documentation generation

2. Which Terraform command is commonly used in CI/CD pipelines to detect drift before applying changes?

easy

A. terraform plan

B. terraform apply

C. terraform init

D. terraform destroy

Solution

1. Step 1: Recall Terraform commands

   terraform plan shows the changes Terraform will make without applying them.

2. Step 2: Identify drift detection command

   terraform plan detects differences (drift) between code and real infrastructure before apply.

3. Final Answer:

   terraform plan -> Option A

4. Quick Check:

   Detect drift = terraform plan [OK]

Hint: Use terraform plan to preview changes [OK]

Common Mistakes:

• Using terraform apply which changes infrastructure
• Confusing terraform init with drift detection
• Using terraform destroy which deletes resources

3. Given the following Terraform plan output snippet in a CI/CD pipeline:

  # aws_instance.example will be updated in-place
  ~ tags = {
      - "Environment" = "dev"
      + "Environment" = "prod"
    }

What does this output indicate about drift?

medium

A. Terraform will ignore the tag change

B. The instance will be destroyed and recreated

C. No drift is detected; tags remain unchanged

D. The tag "Environment" has drifted from "dev" to "prod" and will be updated

Solution

1. Step 1: Analyze the plan output

   The '~' symbol means in-place update. The tag "Environment" changes from "dev" to "prod".

2. Step 2: Understand drift implication

   This shows drift: the real infrastructure tag differs from code and will be updated.

3. Final Answer:

   The tag "Environment" has drifted from "dev" to "prod" and will be updated -> Option D

4. Quick Check:

   ~ means update tag from dev to prod [OK]

Hint: Look for ~ symbol to spot in-place updates [OK]

Common Mistakes:

• Thinking resource will be destroyed instead of updated
• Ignoring tag changes as no drift
• Assuming Terraform ignores tag differences

4. You run terraform plan in your CI/CD pipeline but it does not detect drift even though manual changes were made outside Terraform. What is the most likely cause?

medium

A. Terraform automatically ignores manual changes

B. You forgot to run terraform apply first

C. Terraform state file is outdated or corrupted

D. The provider plugin is missing

Solution

1. Step 1: Understand drift detection dependency

   Terraform relies on the state file to compare real infrastructure with code.

2. Step 2: Identify cause of missed drift

   If the state file is outdated or corrupted, Terraform cannot detect manual changes (drift).

3. Final Answer:

   Terraform state file is outdated or corrupted -> Option C

4. Quick Check:

   State file outdated = missed drift detection [OK]

Hint: Check state file freshness if drift not detected [OK]

Common Mistakes:

• Assuming terraform apply affects drift detection
• Believing Terraform ignores manual changes by design
• Thinking missing provider causes drift detection failure

5. In a CI/CD pipeline, you want to automatically detect drift and fail the pipeline if any drift is found before applying changes. Which approach best achieves this?

hard

A. Run terraform apply directly and rely on errors to detect drift

B. Run terraform plan and parse its output to detect changes, then fail if changes exist

C. Skip drift detection and always apply changes

D. Manually check infrastructure outside the pipeline

Solution

1. Step 1: Understand CI/CD drift detection goal

   The goal is to detect drift and fail early before applying changes.

2. Step 2: Choose correct command and method

   terraform plan shows drift without applying; parsing its output allows pipeline to fail if drift exists.

3. Step 3: Evaluate other options

   Applying directly risks unwanted changes; manual checks are slow; skipping detection is unsafe.

4. Final Answer:

   Run terraform plan and parse its output to detect changes, then fail if changes exist -> Option B

5. Quick Check:

   Plan + parse output = fail on drift [OK]

Hint: Use terraform plan output to gate pipeline success [OK]

Common Mistakes:

• Applying without checking drift first
• Relying on manual checks in automated pipelines
• Ignoring drift detection to speed up deploys