Lambda आणि DynamoDB ने CQRS आणि Event Sourcing Patterns

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

1. रोजचे उदाहरण: वही vs स्कोअरबोर्ड

Kenji (Osaka) notebook append-only; board = projection. Luis (Mexico City, MXN) OrderPlaced events; read table = list screen.

Hands-on: CDC Streams project, ecommerce cart project; depth DynamoDB Streams chapter.

2. CQRS का?

हे का लागतं?

एकच table write+dashboard = scans/contention. Spiky reads writes block करू नयेत.

हे काय आहे?

CQRS = commands vs queries. Event sourcing = events = source of truth.

3. Vertical diagram

4. CQRS without full ES

CQRS light: orders + inbox projection. Full ES: प्रत्येक event कायम — शक्तिशाली आणि जड.

5. How: projection

कसं करायचं (step by step)

1. Commands नाम.
2. Events define.
3. Invariants write side.
4. Projection idempotent.
5. Query ≠ command.
6. Rebuild plan.

6. Commands + meaning

Stream describe

aws dynamodb describe-table --region ap-south-1 --table-name orders-write \
  --query 'Table.StreamSpecification' 

अर्थ: Projection साठी stream view confirm.

ESM list

aws lambda list-event-source-mappings --region ap-south-1 \
  --query 'EventSourceMappings[?contains(EventSourceArn, `dynamodb`)].{F:FunctionArn,S:State,U:UUID}' 

अर्थ: कुठली Lambda कुठल्या stream वर.

Logs filter

aws logs filter-log-events --region ap-south-1 \
  --log-group-name /aws/lambda/orders-projector \
  --filter-pattern 'ERROR' --limit 20 

अर्थ: Projection fail = stale reads.

Read table count

aws dynamodb scan --region ap-south-1 --table-name orders-inbox \
  --select COUNT --max-items 1 

अर्थ: Lab only; prod = metrics.

7. Industries

• Fintech ledger.
• Ecommerce dashboard.
• EdTech streaks.
• Media moderation.
• SaaS seats.

8. Lab

9. Lab - CQRS sketch

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

कसं करायचं (step by step)

1. Paper: loan command/events/read.
2. StreamSpecification.
3. Iterator age alarm.
4. Rebuild plan.

Cleanup (billing थांबवा)

1. ESM disable.
2. Lab cleanup.

10. 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.

11. 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.

12. सामान्य errors आणि fixes

प्रत्येक row = खरी चूक. Panic करण्याआधी fix वाचा.

13. FAQ

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

15. Tips — English, मराठी आणि हिंदी

16. 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.

17. 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.

18. 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.

19. Glossary

20. Practice: मोठ्याने explain

1. 60s: CQRS आणि event sourcing गोष्ट.
2. 60s: sync vs async checkout.
3. 60s: Lambda नको कधी.
4. 60s: DLQ + idempotency.
5. Record ×2.

21. Safe lab hygiene

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

22. या chapter च्या links

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

23. Myths

24. 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.

25. Regional notes (ap-south-1)

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

26. 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.

27. Pre-mortems

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

28. Currency / locale

Currencies आणि names rotate करा — global mental model.

29. Mei appointments (SGD)

1. BookSlot event.
2. Projector.
3. TV = read.
4. Cancel projection.

30. Anti-patterns

• Fat events.
• Always sync proj.
• No replay.

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.