Serverless IaC: SAM vs Serverless Framework vs CDK Compared

By Ravindra Bagale, trainer · LinkedIn · Last updated: 2 November 2026

1. Everyday example: three kitchens, one thali

Priya in Bengaluru (INR) must ship a checkout API. Her teammate knows YAML; another loves TypeScript. Same thali (API Gateway + Lambda + DynamoDB) — different kitchens. Wrong kitchen slows the sprint.

Deep CDK: AWS CDK. Templates under the hood: CloudFormation. Compute: Lambda.

2. Why compare IaC tools?

Why do we need this?

Serverless apps are many small resources. Hand-click console drifts. IaC makes review, rollback, and multi-env possible. Choosing the wrong tool for your team creates glue scripts and abandoned plugins.

What is it?

SAM = AWS-native serverless macros on CloudFormation + sam CLI. Serverless Framework = serverless.yml + plugins. CDK = imperative constructs to CloudFormation.

3. Vertical diagram

4. How: decision table

How to do it (step by step)

5. Per-concept commands

Validate a SAM template (read-only shape)

sam validate --template template.yaml --region ap-south-1

Meaning: Catches obvious template mistakes before deploy.

List CloudFormation stacks (see what IaC owns)

aws cloudformation list-stacks --region ap-south-1 \
  --stack-status-filter CREATE_COMPLETE UPDATE_COMPLETE \
  --query 'StackSummaries[].{N:StackName,T:TemplateDescription}' --output table

Meaning: Inventory before you add another tool.

CDK list stacks in app (if cdk installed)

cdk ls --app "npx ts-node bin/app.ts" 2>/dev/null || echo "install cdk in project first" 

Meaning: Shows stacks the app would synthesize — no deploy.

Diff a change set mindset

aws cloudformation describe-stacks --region ap-south-1 \
  --stack-name checkout-api --query 'Stacks[0].{S:StackStatus,U:LastUpdatedTime}' 

Meaning: Always know last update time before touching prod.

6. CI patterns

• Build then unit test then sam build / cdk synth then deploy to staging then smoke then prod with approval.
• Never deploy from a laptop to prod; use OIDC roles.
• Pin plugin and CDK versions; lockfiles matter.
• Secrets via SSM/Secrets Manager refs — not plaintext in yml.

7. Industries

• Fintech (Aisha, Lagos, NGN): CDK shared banking constructs; auditors love reviews.
• Ecommerce (Rohan, Pune, INR): SAM for small checkout; speed.
• SaaS (Priya, Bengaluru, INR): Serverless Framework plugins for custom domains historically.
• Gov (Omar, Amman, JOD): CloudFormation/SAM for approved patterns.
• Media (Kenji, Osaka, JPY): CDK pipelines for many Lambda image jobs.

8. Lab

9. Lab - inspect, do not invent a fourth tool

Do this in ap-south-1 (Mumbai) unless your org forbids it. Set a budget alert first.

How to do it (step by step)

1. List stacks in ap-south-1; note which look SAM/CDK named.
2. Open the linked CDK chapter; skim construct idea.
3. Write 5 lines: which tool your team would pick and why.
4. sam validate on a sample template if you have one.

Cleanup (stop billing)

1. Do not leave experimental stacks.
2. Delete any lab stack you create.

10. Same pattern across industries

• Fintech (Aisha, Lagos): payment webhooks → SQS → Lambda; never block the bank callback thread.
• Ecommerce (Rohan, Pune): checkout API on API Gateway+Lambda; inventory fan-out on SNS.
• Healthcare (Mei, Singapore): appointment SMS via SNS; PHI stays in DynamoDB with fine-grained IAM.
• EdTech (Diego, São Paulo): nightly cleanup EventBridge → Lambda on student drafts.
• Logistics (Fatima, Casablanca): package scan events on EventBridge bus; Step Functions for customs saga.
• Media (Kenji, Osaka): S3 upload → Lambda thumbnails; fan-out to moderation + CDN invalidate.
• SaaS multi-tenant (Priya, Bengaluru): Cognito groups + DynamoDB partition per tenant.
• Gov portal (Omar, Amman): strangler fig — peel one PDF form route per sprint to Lambda.

11. Troubleshooting checklist

1. Confirm region (ap-south-1 vs us-east-1 for CloudFront/ACM quirks).
2. Check CloudWatch Logs for the function name and request id.
3. Verify IAM execution role allows the API you call.
4. For async: check DLQ depth and SQS age of oldest message.
5. For APIs: curl -v and compare status, CORS headers, body.
6. For workflows: open Step Functions execution event history.
7. Re-read the linked deep chapter before reinventing a service.
8. If cost spikes: check concurrency, retries, and provisioned capacity.

12. Common errors and fixes

Each row is a real mistake students and juniors hit. Read the fix before you panic.

13. FAQ

14. Interview Q&A (Beginner / Mid / Senior + MNC)

15. Tips in English, Marathi and Hindi

16. Architecture decision checklist

1. Write the user journey in five bullets with no AWS names.
2. Mark each step sync (user waits) or async.
3. Name failure mode: retry, DLQ, compensate, or alert-only.
4. Name the idempotency key for every write.
5. Pick data store from access patterns (link DynamoDB modeling).
6. Estimate monthly cost at 1x and 10x traffic (USD and INR).
7. Confirm account concurrency and service quotas in ap-south-1.
8. Decide auth: Cognito, IAM, Lambda authorizer, or none.
9. Name on-call and which CloudWatch alarm pages them.
10. Link the deep chapter you will not rewrite.
11. Only then open console or IaC.

17. Copy-paste quick commands (read-only first)

# Region and identity
aws configure get region
aws sts get-caller-identity

# Lambda landscape
aws lambda list-functions --region ap-south-1 --max-items 20 \
  --query 'Functions[].{N:FunctionName,R:Runtime,T:Timeout,M:MemorySize}' --output table
aws lambda get-account-settings --region ap-south-1

# API Gateway (HTTP APIs)
aws apigatewayv2 get-apis --region ap-south-1 --query 'Items[].{N:Name,Id:ApiId,Ep:ProtocolType}' --output table

# Queues and topics
aws sqs list-queues --region ap-south-1
aws sns list-topics --region ap-south-1 --query 'Topics[].TopicArn'

# Event buses and state machines
aws events list-event-buses --region ap-south-1
aws stepfunctions list-state-machines --region ap-south-1 --query 'stateMachines[].name'

# DynamoDB tables (names only)
aws dynamodb list-tables --region ap-south-1

Run these in a sandbox account. Prefer read-only IAM while learning.

18. More industry and stack stories

• Fintech (Aisha, Lagos, NGN): bank webhooks must return 200 fast — SQS absorbs spikes; ledger Lambda is idempotent on paymentId.
• Ecommerce (Rohan, Pune, INR): Black Friday — API Gateway throttle + SQS order intake; SNS fans inventory, email, analytics.
• Healthcare (Mei, Singapore, SGD): appointment reminders via SNS SMS; PHI only in DynamoDB with condition keys.
• EdTech (Diego, São Paulo, BRL): EventBridge nightly cleanup of draft quizzes; Lambda timeout 30s, not 15 min.
• Logistics (Fatima, Casablanca, MAD): package scans on custom EventBridge bus; Step Functions customs saga.
• Media (Kenji, Osaka, JPY): S3 → Lambda thumbnails; never write thumbs to the watched prefix.
• SaaS (Priya, Bengaluru, INR): Cognito groups + DynamoDB PK tenantId; one Lambda authorizer for all routes.
• Gov (Omar, Amman, JOD): strangler — peel one PDF form route per sprint from the monolith.
• Startup (Sofia, Sofia, EUR): start with Function URL for demos; move to HTTP API when partners need JWT.
• Retail (Luis, Mexico City, MXN): store POS sync via SQS FIFO when order matters; Standard when it does not.

• Python: handlers thin; put domain logic in plain modules for unit tests without Lambda.
• Node: prefer async/await; never block the event loop on sync DNS.
• Java: SnapStart for cold starts; keep dependencies lean.
• .NET: AspNetCoreServer for low-traffic tenants; watch package size.
• Go: single static binary; great for SQS workers.
• PHP: keep Laravel queues on ECS; Lambda for S3/webhooks glue.

19. Glossary (short)

20. Practice: explain out loud

1. 60 seconds: everyday story for serverless IaC tools.
2. 60 seconds: sync vs async with a checkout example.
3. 60 seconds: when you refuse Lambda.
4. 60 seconds: DLQ + idempotency in one breath.
5. Record once; cut fillers; record again.

21. Safe lab hygiene

• Tag every lab resource with owner and expiry date.
• Set a monthly AWS Budget alarm in INR or USD before experiments.
• Prefer read-only commands first; mutate in a sandbox account.
• Delete queues, APIs, tables you created — DynamoDB and APIGW leave footprints.
• Never put production secrets in env vars or screenshots.
• Do not enable provisioned concurrency for a hello-world.

22. How this chapter links others

• Compute depth: Lambda.
• HTTP edge: API Gateway.
• Data modeling: DynamoDB.
• Messaging: SQS/SNS.
• Events: EventBridge.
• Workflows: Step Functions.
• Project chapters (build-*): worked assemblies — link, do not paste.

23. Myths to drop

24. Error budget thinking for serverless

If your monthly error budget is 0.1% on checkout, a fan-out that retries aggressively can burn the budget with duplicate emails while money stays correct. Separate business correctness SLOs from notification SLOs.

1. Write two SLOs: money-correct and notify-delivered.
2. Retries on money path: bounded + idempotent.
3. Retries on notify path: best-effort + DLQ.
4. Page humans on money DLQ; ticket on notify DLQ.

25. Regional notes (ap-south-1)

• Build labs in Mumbai (ap-south-1) unless your org mandates elsewhere.
• Some services launch first in us-east-1 — check feature availability.
• Data residency for INR fintech may require in-region only.
• Latency to end users in India usually favors ap-south-1.

26. Naming conventions that save incidents

# Suggested prefixes
# Lambda:  pay-intake-prod, pay-worker-prod
# SQS:     pay-orders.fifo / pay-orders-dlq
# SNS:     pay-order-events
# EB bus:  pay.domain
# SFN:     pay-refund-saga
# DDB:     pay-orders-prod

Include env (dev/stage/prod) and domain. Future you grepping CloudWatch will thank present you.

27. Pre-mortems (ten minutes)

1. Imagine tomorrow headline: double charge in AED. What broke?
2. Imagine DLQ depth 50,000 after a bad deploy. How do you drain?
3. Imagine Cognito outage. Do APIs fail closed or serve read-only?
4. Write answers in the runbook before go-live.

28. Currency and locale in examples

Rotate currencies in designs: INR, USD, EUR, AED, NGN, BRL, JPY, SGD. Rotate names: Aisha, Rohan, Mei, Diego, Fatima, Kenji, Priya, Omar, Sofia, Luis. This keeps mental models global — not one-country samples.

29. Worked story: Priya chooses CDK (INR)

1. Three microservices share auth and table grants.
2. YAML copy-paste drifts.
3. CDK construct library centralizes IAM.
4. Pipeline synth+diff catches sneaky IAM widen.

30. Anti-patterns

• New tool every sprint.
• Deploying with admin keys from laptops.
• Ignoring change set review.

Revision, interview and comparison cards

Revise this lesson in a few minutes. Save the cards on your phone or download them as PNG files. The QR code on each card opens this lesson.

More cards: Ravi Sir's Cards.