Re-architecting migrated workloads

Bundled into the existing AWS Certified Solutions Architect - Professional premium course — no separate purchase.

Included in this chapter:

Dimension	EC2 (rehost/replatform)	ECS on Fargate	EKS	Lambda
Operational ownership	OS + runtime + scaling you own	Runtime only; no hosts	K8s control plane managed; you run workloads	None (fully serverless)
Best fit	Custom kernel, GPU, licensed AMI, lift-and-shift	Stateless/containerized services, AWS-native	Existing Kubernetes / portability needs	Short event-driven functions
Hard limits to watch	You patch and scale the fleet	Task CPU/memory sizing	Per-cluster cost + K8s skills	15-min run, 6 MB sync payload, 10 GB mem
Scaling model	Auto Scaling groups	Service Auto Scaling per task	Cluster Autoscaler / Karpenter / HPA	Automatic, per-request concurrency
Migration fit	Fastest target after rehost	Replatform (containerize, drop hosts)	Replatform if already on Kubernetes	Refactor (re-write to functions)

Cheat sheet

Walk the managed-service ladder, stop at first fit
Lambda's hard limits disqualify long or heavy work
Fargate removes the host fleet; the EC2 launch type doesn't
ECS for lowest ops, EKS for existing Kubernetes
EKS is certified Kubernetes-conformant, so manifests run unchanged
Same image runs on ECS or EKS, pulled from ECR
App2Container containerizes .NET/Java without source code
Replatform a self-managed DB to RDS, refactor to Aurora
SCT converts the schema; DMS moves the data
Babelfish keeps SQL Server clients on Aurora PostgreSQL
Refactor to DynamoDB only for key-based access at scale
ElastiCache and OpenSearch are purpose-built offload targets
Strangler fig decomposes a monolith incrementally
An anti-corruption layer protects the new service model
Decouple services with SQS, SNS, EventBridge, or Step Functions
Step Functions: Standard exactly-once, Express at-least-once
Externalize state to S3, EFS, or FSx to make compute stateless
Use Aurora Serverless v2 (not v1) to scale down on idle
Re-architecting is the target design, not the move itself
Fargate task definitions require awsvpc, task-level CPU/memory, and an execution role
API Gateway REST usage plans give per-client throttling via API keys

Unlock with Premium — includes all practice exams and the complete study guide.

Cheat sheet