SNS, SQS आणि Step Functions ने Fan-Out आणि Fan-In Patterns

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

1. रोजचे: घंटा आणि sports board

Rohan (Pune): SNS OrderPlaced → inventory/invoice/analytics. Fraud checks Parallel → join = fan-in.

Hands-on: order fanout project. SQS/SNS. Step Functions.

2. Fan-out का?

हे का लागतं?

Sync तीन Lambda = coupled timeouts. Fan-out = स्वतंत्र scale/fail.

हे काय आहे?

Fan-out: एक → अनेक. Fan-in: अनेक → एक next.

3. Vertical diagrams

4. SNS vs EB vs Parallel

5. How: safe fan-out

कसं करायचं (step by step)

1. Topic.
2. Queues+DLQ subscribe.
3. Raw delivery choice.
4. ESM per queue.
5. IAM split.
6. Test ×3.
7. DLQ alarms.

Subscriptions

aws sns list-subscriptions-by-topic --topic-arn $TOPIC --region ap-south-1

अर्थ: तीन SQS subs confirm.

Publish test

aws sns publish --topic-arn $TOPIC --region ap-south-1 \
  --message '{"orderId":"o-42","currency":"INR","total":499}'

अर्थ: तीन queues depth बघा.

6. Fan-in

• SFN Parallel.
• Map + cap.
• DDB counter risky.
• No busy-poll.

Python buffer?

def needs_queue(consumer_slow, spike_expected):
    return consumer_slow or spike_expected
print(needs_queue(True, False))
print(needs_queue(False, False))

Output: True/False. अर्थ: slow/spiky → SQS.

7. Failure isolation

Invoice fail ≠ inventory fail. Luis (Mexico City) sync for-loop मुळे stock अडकला.

8. Lab

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

कसं करायचं (step by step)

1. Draw + DLQs.
2. FIFO vs Standard.
3. Optional sandbox.
4. Publish verify.
5. Cleanup.

Cleanup (billing थांबवा)

1. Unsub then delete.
2. Lambdas/logs.

9. Map concurrency

Map MaxConcurrency सेट करा; fragile API आधी SQS.

Queue depth

aws sqs get-queue-attributes --queue-url $Q --attribute-names ApproximateNumberOfMessages ApproximateNumberOfMessagesNotVisible --region ap-south-1

अर्थ: Depth ↑ = consumer lag.

10. Fan-out idempotency

Duplicates येतात. orderId conditional put. Kenji (Osaka) जपान Yen invoices दुप्पट.

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. Fan-out poison/redrive

1. Per-consumer DLQ.
2. Alarm → team.
3. Redrive that DLQ.
4. Inspect sample first.

18. Security

• Topic Publish policy.
• Queue allow SNS ARN.
• Least privilege consume.
• SSE/KMS.

19. Cost

Isolation खरेदी. Labs free tier; Black Friday scale = watch SQS+concurrency.

Filter policy

# Subscription attribute FilterPolicyJSON
# {"currency":["INR","AED"],"type":["OrderPlaced"]}

अर्थ: Matching currency लाच wake.

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: fan-out आणि fan-in 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.

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अजून cards: Ravi Sir's Cards.