cloud-platform-skills / skills

---
description: "AWS migration planning: the 6Rs framework (rehost, replatform, refactor, repurchase, retain, retire), discovery and wave planning, MGN server migration, DMS data cutover with CDC, and rollback criteria. Use when planning a datacenter exit or lease expiry, deciding whether a legacy monolith should be rehosted or refactored, or moving a large Oracle, SQL Server or Postgres database with minimal downtime."
globs:
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---

# AWS Cloud Migration: The 6Rs Framework & Migration Automation

## When to Use This Skill

**Triggers — load this skill when:**

- A workload portfolio must be assessed and assigned migration strategies
- Migration waves, dependencies, and cutover windows need planning
- Data must move with minimal downtime (DMS/MGN) and a rollback path

**Route elsewhere when:**

- Post-migration cost governance -> `finops-framework-inform-optimize-operate`
- Target-state Kubernetes design -> `aws-eks-enterprise-patterns`
- Schema change mechanics -> `database-devops-lifecycle`

## 1. The 6Rs Migration Decision Tree

```text
                      [Workload Assessment]
                                |
        +-----------------------+-----------------------+
        |                                               |
  [Low Change / Fast]                         [Modernize / Optimize]
        |                                               |
   +----+----+                                     +----+----+
   |         |                                     |         |
Rehost   Replatform                            Refactor  Repurchase
(Lift &   (Managed DB /                         (Serverless / (SaaS replacement)
 Shift)   Containers)                           Microservices)
```

---

## 2. Zero-Downtime Data Migration with AWS DMS (Terraform)

```hcl
resource "aws_dms_replication_instance" "dms_instance" {
  replication_instance_id    = "dms-migration-instance"
  replication_instance_class = "dms.r5.xlarge"
  allocated_storage          = 100
  multi_az                   = true
  vpc_security_group_ids     = [aws_security_group.dms_sg.id]
  replication_subnet_group_id = aws_dms_replication_subnet_group.dms_subnet_group.id
}

resource "aws_dms_replication_task" "continuous_cdc" {
  replication_task_id      = "mysql-to-aurora-cdc"
  migration_type           = "full-load-and-cdc" # Initial load + continuous replication
  replication_instance_arn = aws_dms_replication_instance.dms_instance.replication_instance_arn
  source_endpoint_arn      = aws_dms_endpoint.onprem_mysql.endpoint_arn
  target_endpoint_arn      = aws_dms_endpoint.aws_aurora.endpoint_arn
  table_mappings           = jsonencode({
    rules = [{
      "rule-type" = "selection",
      "rule-id"   = "1",
      "rule-name" = "replicate-all",
      "object-locator" = { "schema-name" = "%", "table-name" = "%" },
      "rule-action"    = "include"
    }]
  })
}
```

---

## 3. Best Practices & Anti-Patterns

- **Do**: Perform continuous CDC (Change Data Capture) replication to achieve near-zero downtime during the final DNS cutover.
- **Don't**: Never migrate workloads without prior discovery dependency mapping (AWS Application Discovery Service).

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