Strangler Fig Pattern: Monolith मधून Serverless कडे Step by Step

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

1. रोजचे उदाहरण: बस तिकीट खिडकी

Omar (Amman, JOD) gov portal. एक URL. पहिले /forms/birth-cert = Lambda; बाकी Tomcat. Fail तर तोच path परत. Strangler fig.

Edge: API Gateway. Greenfield: REST API project, notes app — strangler = coexist.

2. Strangle का?

हे का लागतं?

Big-bang slip. Risk एका cutover मध्ये. Strangle = sprint-by-sprint proof; revenue चालू.

हे काय आहे?

Strangler fig = facade → selected paths to Lambda; जुने paths नंतर retire.

3. Vertical diagram

4. How: एक route

कसं करायचं (step by step)

1. Traffic+pain inventory.
2. Leaf route first.
3. Facade.
4. Contract tests.
5. Canary/shadow.
6. 100% + rollback.
7. Delete late.

5. Commands + meaning

HTTP API routes

aws apigatewayv2 get-routes --region ap-south-1 --api-id "$API_ID" \
  --query 'Items[].{R:RouteKey,T:Target}' --output table

अर्थ: कुठले paths Lambda vs proxy.

ALB rules

aws elbv2 describe-rules --region ap-south-1 --listener-arn "$LISTENER_ARN" \
  --query 'Rules[].{P:Priority,C:Conditions[0].PathPatternConfig.Values[0]}' --output table

अर्थ: Path rules = peel map.

Canary errors

aws cloudwatch get-metric-statistics --region ap-south-1 \
  --namespace AWS/Lambda --metric-name Errors --dimensions Name=FunctionName,Value=birth-cert-api \
  --start-time $(date -u -d '1 hour ago' +%Y-%m-%dT%H:%M:%S) --end-time $(date -u +%Y-%m-%dT%H:%M:%S) \
  --period 300 --statistics Sum

अर्थ: Canary Errors वाढले तर flip back.

Access log check

# On monolith host (example): count hits to migrated path last hour
sudo grep '/forms/birth-cert' /var/log/nginx/access.log | tail -20

अर्थ: 100% नंतर monolith quiet.

6. Data coexist

7. कधी नको

• आधी DNS/domain.
• Contract tests नसतील तर थांबा.
• Audit flag.
• आधी seam.

8. Industries

• Gov forms.
• Bank statements.
• Retail store-finder.
• EdTech PDF.
• SaaS webhooks.

9. Lab

10. Lab - peel plan

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

कसं करायचं (step by step)

1. Leaf vs core mark.
2. Facade choice.
3. Metrics.
4. Rollback 5 bullets.
5. Optional lab API.

Cleanup (billing थांबवा)

1. Cleanup.
2. Alarms.

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. 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.

18. 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.

19. 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.

20. Glossary

21. Practice: मोठ्याने explain

1. 60s: strangler fig migration गोष्ट.
2. 60s: sync vs async checkout.
3. 60s: Lambda नको कधी.
4. 60s: DLQ + idempotency.
5. Record ×2.

22. Safe lab hygiene

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

23. या chapter च्या links

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

24. Myths

25. 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.

26. Regional notes (ap-south-1)

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

27. 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.

28. Pre-mortems

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

29. Currency / locale

Currencies आणि names rotate करा — global mental model.

30. Priya webhooks (INR)

1. BF overload.
2. Peel to Lambda.
3. Canary then 100%.
4. Delete late.

31. Anti-patterns

• DB+API day one.
• No parity.
• Wrong order.

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.