Table of Contents

Introduction

Migrating from manually managed cloud infrastructure to Terraform is one of the highest-impact improvements a team can make. This guide walks you through the entire migration strategy — from assessment to full automation.

Need help with enterprise migrations? OpenEmpower is an AWS Silver Partner offering managed migration services.

The Migration Path

Phase 1: Assessment

Before writing any Terraform code, audit your current infrastructure:

# List all AWS resources
aws resourcegroupstaggingapi get-resources --output json > resources.json

# Count resources by service
cat resources.json | jq '.ResourceTagMappingList[].ResourceARN' | \
  cut -d: -f3 | sort | uniq -c | sort -rn

Phase 2: Import Existing Resources

# Terraform 1.5+ import blocks
import {
  to = aws_instance.web
  id = "i-abc123def456"
}

import {
  to = aws_vpc.main
  id = "vpc-xyz789"
}

# Generate configuration from imports
terraform plan -generate-config-out=generated.tf

Phase 3: Modularize

Break imported resources into logical modules:

terraform/
├── modules/
│   ├── networking/    # VPC, subnets, security groups
│   ├── compute/       # EC2, ASG, ALB
│   ├── database/      # RDS, ElastiCache
│   └── monitoring/    # CloudWatch, SNS
├── environments/
│   ├── dev/
│   ├── staging/
│   └── production/
└── global/            # IAM, Route53, S3

Phase 4: CI/CD Pipeline

Automate Terraform with your CI/CD system:

# GitLab CI example
stages:
  - validate
  - plan
  - apply

validate:
  script:
    - terraform fmt -check
    - terraform validate
    - tflint

plan:
  script:
    - terraform plan -out=tfplan
  artifacts:
    paths: [tfplan]

apply:
  script:
    - terraform apply tfplan
  when: manual
  only: [main]

Phase 5: Governance

Implement policy-as-code:

# Example: OPA policy
package terraform

deny[msg] {
  resource := input.resource_changes[_]
  resource.type == "aws_instance"
  not resource.change.after.tags.Environment
  msg := "All instances must have an Environment tag"
}

Common Migration Mistakes

  1. Trying to import everything at once — start with non-critical resources
  2. Ignoring state management — set up remote state FIRST
  3. Skipping testing — use Terratest or terraform validate
  4. No rollback plan — keep manual access until Terraform is proven
  5. Forgetting about drift — schedule regular terraform plan checks

Enterprise Migration Support

For organizations needing hands-on help:

Hands-On Courses

Learn by doing with interactive courses on CopyPasteLearn:

Conclusion

Migrating to Terraform is a journey, not a destination. Start small, build confidence, and gradually bring more infrastructure under code management. The investment pays off in reliability, repeatability, and team velocity.