Event sourcing microserices with Azure

Event Sourcing + CQRS – Azure BFSI Microservices

1. Overview of Event Sourcing + CQRS

• Event Sourcing: Persist domain events (LoanApproved, SIPExecuted, WalletCredited) in Event Hub instead of final state.

• CQRS (Command Query Responsibility Segregation):

  • Command side: Writes events to Event Hub.

  • Query side: Projections created in Cosmos DB/Azure SQL for fast reads and dashboards.

• Analytics & Compliance: Long-term event storage in Azure Data Lake (WORM) → analysis via Synapse Analytics.

Use Case 1: Loan Microservices (Event Sourcing + CQRS)

Text Diagram

[Loan Application Command API]

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Azure API Management (APIM)

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Loan Service (Command) → Event Hub (LoanEvents)

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+----> Cosmos DB (Read Model – Loan Status)

+----> Azure SQL (Projections – Disbursement)

+----> Azure Data Lake (Immutable Audit – RBI)

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Synapse Analytics → Power BI (Compliance Dashboard)

Step-by-Step Flow

1. Command Side (Write Events)

   • Loan Service validates application → emits LoanApplied event to Event Hub.

   • Subsequent events: KYCVerified, CreditChecked, FraudCheckPassed, LoanApproved.

2. Event Storage

   • Event Hub serves as immutable event log (10-year retention for RBI compliance).

3. Projection (Query Side)

   • Azure Functions/Stream Analytics consume Event Hub events:

     • Update Cosmos DB: Loan status, approval progress (for mobile app).

     • Update Azure SQL: Payment/disbursement projections for finance team.

4. Analytics

   • Event Hub archives → Azure Data Lake (WORM) → Synapse Analytics for reporting (loan volumes, NPA analysis).

5. Multi-Tenancy

   • Separate Event Hub namespaces or partitions per bank (ICICI, HDFC) for isolation.

Use Case 2: Mutual Fund Microservices (Event Sourcing + CQRS)

Text Diagram

[SIP/Redemption Command API]

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APIM (Tenant-aware JWT)

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SIP Service / Redemption Service → Event Hub (MFEvents)

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+----> Cosmos DB (Portfolio Read Model)

+----> PostgreSQL (NAV Projections)

+----> Azure Data Lake (SEBI Audit Logs)

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Synapse Analytics → Power BI (Investor Reports)

Step-by-Step Flow

1. Command Side (Write)

   • SIP Service emits SIPRegistered, SIPExecuted events to Event Hub.

   • Redemption Service emits RedemptionRequested, RedemptionSettled events.

2. Projection Side (Read)

   • Cosmos DB stores portfolio projections (per investor, per scheme).

   • PostgreSQL (or Azure SQL) stores NAV snapshots for daily reporting.

3. Analytics

   • Event Hub → Data Lake (SEBI requires 7-year retention of NAV/SIP logs).

   • Synapse + Power BI dashboards for investor insights, compliance reports.

4. Tenant Isolation

   • API Management injects tenant ID into event metadata → partitions projections in Cosmos DB.

Use Case 3: Digital Wallet Microservices (Event Sourcing + CQRS)

Text Diagram

[Wallet Transaction Command API]

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Azure API Management

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Transaction Service (Command) → Event Hub (WalletEvents)

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+----> Cosmos DB (Real-time Balance Projection)

+----> Azure SQL (Ledger for Reconciliation)

+----> Azure Data Lake (RBI Audit Trail)

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Synapse Analytics → Power BI (Fraud/Usage Reports)

Step-by-Step Flow

1. Command Side

   • Wallet top-up, payment, transfer events emitted (WalletCredited, WalletDebited).

2. Event Storage

   • Event Hub captures immutable transaction events.

3. Projections (Query Side)

   • Cosmos DB: Near real-time balance queries for mobile app.

   • Azure SQL: Ledger-style reconciliation for finance back-office.

4. Fraud Detection

   • Event Hub events streamed to Azure ML (Kafka endpoint) for anomaly detection.

5. Compliance

   • Immutable logs archived to Data Lake (RBI requires 10-year retention).

Azure Services Used (Common Across All)

• Event Hub: Kafka-compatible event store for write side

• Cosmos DB: Low-latency projections (read side)

• Azure SQL/PostgreSQL: Aggregated projections (finance, compliance)

• Azure Data Lake: Long-term immutable storage (WORM lock for RBI/SEBI)

• Synapse Analytics: BI/reporting (loan portfolio, SIP activity, wallet fraud patterns)

• Power BI: Dashboards for CXOs, auditors, regulators

• Azure Functions/Stream Analytics: Real-time projection updates

Multi-Tenant Architecture (SaaS BFSI)

• Event Hub Namespaces: One per tenant (ICICI, HDFC) OR partition keys per tenant

• Cosmos DB: Partition by tenantId for isolated projections

• API Management: JWT token includes tenantId, propagated to events

Text Diagram (Combined Multi-Tenant CQRS Flow)

[API Management (Tenant-aware)] --> [Event Hub (Partitioned by Tenant)]

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|----> [Cosmos DB (Per-tenant projections for Mobile/Web)]

|----> [Azure SQL/PostgreSQL (Finance & Compliance projections)]

|----> [Azure Data Lake (Immutable WORM logs)]

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[Synapse Analytics + Power BI → Regulatory Dashboards (RBI/SEBI)]