API Gateway, Lambda आणि DynamoDB ने Serverless API Backend Pattern

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

1. रोजचे उदाहरण: फूड कार्ट

Meera (Pune) momo cart: खिडकी = पेमेंट; किचन सार्वजनिक नाही. API Gateway = HTTPS खिडकी; DynamoDB = ticket.

तुम्ही URL shortener project आणि REST API project मध्ये variants केले. इथे pattern आणि design choices.

2. हे pattern का?

हे का लागतं?

EC2 public IP, TLS विसरणं, gateway मध्ये business logic — pattern तीन boxes स्वच्छ ठेवतो.

हे काय आहे?

Serverless API backend = HTTPS edge + Lambda + data + IAM.

3. Vertical diagram

4. HTTP vs REST vs Function URL

5. How: request path

कसं करायचं (step by step)

1. Routes कागदावर.
2. Table from access patterns.
3. Lambda handler.
4. Least-privilege role.
5. HTTP API + CORS.
6. Auth + throttle.
7. curl + logs.
8. Optional SNS.

HTTP API create

aws apigatewayv2 create-api --name meera-momo-api --protocol-type HTTP --region ap-south-1 \
  --query '{Id:ApiId,Ep:ApiEndpoint}'

अर्थ: Invoke URL मिळते. Lab नंतर delete.

Route wire

aws apigatewayv2 create-integration --api-id $API --integration-type AWS_PROXY \
  --integration-uri $LAMBDA_ARN --payload-format-version 2.0 --region ap-south-1

अर्थ: AWS_PROXY = पूर्ण HTTP event.

6. Status codes

7. Mini-examples

Python response

def ok(body, code=200):
    import json
    return {"statusCode": code, "headers": {"content-type": "application/json"},
            "body": json.dumps(body)}
print(ok({"orderId": "o-1"}, 201)["statusCode"])

Output: 201. अर्थ: statusCode महत्त्वाचा.

Node validate

exports.handler = async (event) => {
  if (!event.body) return {statusCode: 400, body: '{"error":"empty"}'};
  return {statusCode: 200, body: event.body};
};

अर्थ: DynamoDB आधी fail fast.

curl smoke

curl -sS -X POST "$API_URL/orders" -H 'content-type: application/json' \
  -d '{"sku":"MOMO-STEAM","qty":2,"currency":"INR"}'

अर्थ: 201 + orderId किंवा 400.

8. Lab: sketch + optional API

Org block नसेल तर ap-south-1 (Mumbai). आधी budget alert.

कसं करायचं (step by step)

1. Routes+keys+codes.
2. Optional sandbox.
3. curl + request ids.
4. Throttle → 429.
5. Cleanup.

Cleanup (billing थांबवा)

1. API → Lambda → table → role.
2. Log group.

9. Auth आणि multi-tenant

JWT gateway वर. Cognito. SaaS: tenantId token+PK — फक्त body वर विश्वास नका.

10. CORS

Browser CORS हवा; native mobile ला नको.

Routes

aws apigatewayv2 get-routes --api-id $API --region ap-south-1 --query 'Items[].RouteKey'

अर्थ: Routes confirm.

11. एकाच pattern — वेगवेगळ्या industries

• Fintech (Aisha, Lagos): payment webhooks → SQS → Lambda.
• Ecommerce (Rohan, Pune): checkout API; inventory SNS fan-out.
• Healthcare (Mei, Singapore): SNS SMS; PHI + fine-grained IAM.
• EdTech (Diego, São Paulo): EventBridge nightly cleanup.
• Logistics (Fatima, Casablanca): EventBridge + saga.
• Media (Kenji, Osaka): S3 → Lambda thumbs + fan-out.
• SaaS (Priya, Bengaluru): Cognito + per-tenant partition.
• Gov (Omar, Amman): strangler fig per form route.

12. Troubleshooting checklist

1. Region confirm करा.
2. CloudWatch Logs + request id.
3. Execution role permissions.
4. DLQ + oldest message age.
5. curl -v + CORS.
6. SFN event history.
7. Linked chapter पुन्हा वाचा.
8. Cost: concurrency/retries.

13. सामान्य errors आणि fixes

प्रत्येक row = खरी चूक. Panic करण्याआधी fix वाचा.

14. FAQ

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

16. Tips — English, मराठी आणि हिंदी

17. Payload आणि pagination

1. Large files → S3 keys.
2. nextToken; no unbounded.
3. content-type check.
4. Idempotency-Key.

18. Aliases नी blue/green

Versions + alias live; weighted shift. Integration = alias ARN, $LATEST नको.

Publish version

aws lambda publish-version --function-name meera-orders --region ap-south-1 --query Version

अर्थ: Rollback साठी version pin.

19. Contract tests

CI मध्ये curl contract tests — checkout customers आधी.

20. Architecture decision checklist

1. User journey 5 bullets, no AWS names.
2. Sync vs async mark.
3. Failure mode.
4. Idempotency key.
5. Data from access patterns.
6. Cost 1x and 10x.
7. Quotas ap-south-1.
8. Auth decision.
9. On-call + alarm.
10. Deep chapter link.
11. मग console/IaC.

21. Copy-paste quick commands

# 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

Sandbox + read-only IAM.

22. अजून industry आणि stack stories

• Fintech Lagos: webhook → SQS → idempotent ledger.
• Ecommerce Pune: throttle + fan-out.
• Healthcare SG: SNS + PHI IAM.
• EdTech: EventBridge cleanup.
• Logistics: bus + saga.
• Media: avoid recursive S3.
• SaaS: tenant partition.
• Gov: strangler peel.
• Startup: Function URL → HTTP API.
• Retail: FIFO vs Standard.

• Python: thin handlers.
• Node: async/await.
• Java: SnapStart.
• .NET: package size.
• Go: static binary.
• PHP: hybrid.

23. Glossary

24. Practice: मोठ्याने explain

1. 60s: serverless API backend गोष्ट.
2. 60s: sync vs async checkout.
3. 60s: Lambda नको कधी.
4. 60s: DLQ + idempotency.
5. Record ×2.

25. Safe lab hygiene

• Tag owner+expiry.
• Budget alarm आधी.
• Read-only first.
• Cleanup.
• No secrets in env/screenshots.
• No provisioned on hello.

26. या chapter च्या links

• Compute: Lambda.
• HTTP: API Gateway.
• Data: DynamoDB.
• Messaging: SQS/SNS.
• Events: EventBridge.
• Workflows: Step Functions.
• build-* projects link.

27. Myths

28. Serverless error budget

Checkout error budget 0.1% असेल तर aggressive retries email duplicates देऊन budget जाळू शकतात. Money SLO ≠ notify SLO.

1. दोन SLOs.
2. Money retries bounded.
3. Notify best-effort.
4. Money page; notify ticket.

29. Regional notes (ap-south-1)

• Labs Mumbai.
• Feature availability.
• Data residency.
• Latency India.

30. Naming conventions

# 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

env + domain नावात ठेवा. CloudWatch grep सोपा.

31. Pre-mortems

1. Double charge headline.
2. DLQ drain plan.
3. Cognito outage mode.
4. Runbook.

32. Currency / locale

Currencies आणि names rotate करा — global mental model.

उजळणी, मुलाखत आणि तुलना cards

हा lesson काही मिनिटांत revise करा. Cards phone वर save करा किंवा PNG download करा. प्रत्येक card वरचा QR हा lesson उघडतो.

अजून cards: Ravi Sir's Cards.