System Design: End-to-End Online Loan Application Platform
Context
Design a small online lending platform where applicants select loan products and submit applications. The platform performs internal review/underwriting and integrates with third-party providers to fetch credit history and bank-account transaction data.
Assume a web/mobile client, US-based compliance (KYC/AML), ACH bank disbursement via a payment/fintech provider, and standard third-party vendors (e.g., credit bureau, bank aggregation, identity/AML).
Requirements
Describe the following:
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High-level architecture
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Service boundaries and core data models
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Public/internal APIs and webhooks
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Eventing/queues/workflows and an application state machine
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Decisioning and post-decision flows
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Approval/denial paths
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Post-decision actions including funds disbursement/transfer
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Operational concerns
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Idempotency, retries, timeouts, rate limiting, partial failures with external APIs
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KYC/AML and fraud checks implementation approach
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PII protection and compliance/audit support
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Manual review tooling
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Observability, scalability, and backpressure under growth
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Compare synchronous vs asynchronous processing and justify trade-offs