Architecting a High-Volume Event-Driven CRM & Webhook Engine
Handling millions of concurrent incoming financial transactions and cross-border webhooks with sub-millisecond ingestion, strict deduplication, and zero message loss.
A European FinTech was experiencing lost webhook payloads from payment processors during peak market movements, causing customer account discrepancies and manual support triage.
Bursty traffic spikes of 10,000 requests/second from disparate banks, erratic network timeouts, and asynchronous status callbacks that frequently arrive out of order.
+-------------------------------------------------------------------------+
| EXTERNAL PARTNERS & PAYMENT GATEWAYS |
| (Stripe, SEPA, Banking Webhooks, Twilio) |
+------------------------------------+------------------------------------+
| HTTP POST Webhooks
v
+-------------------------------------------------------------------------+
| EDGE INGESTION GATEWAY |
| - Instant HMAC Signature Validation |
| - Extracts 'Idempotency-Key' or 'Event-ID' |
| - Redis Atomic SETNX: returns HTTP 200 within 12ms |
+------------------------------------+------------------------------------+
| Pushes Raw Payload
v
+-------------------------------------------------------------------------+
| MESSAGE BUFFER QUEUE |
| - Redis Streams / AWS SQS FIFO |
| - Partitioned by Account Hash (guarantees per-account ordering) |
+------------------------------------+------------------------------------+
|
v
+-------------------------------------------------------------------------+
| DURABLE EVENT PROCESSORS |
| - Deserializes payload & checks state sequence machine |
| - Transactional Outbox Pattern to update Postgres ledger |
| - Emits WebSocket notification to user dashboard |
+------------------------------------+------------------------------------+
| Unrecoverable Failures
v
+-------------------------------------------------------------------------+
| DEAD-LETTER QUEUE |
| - Retains malformed payloads for forensic playback & alert triage |
+-------------------------------------------------------------------------+Core Technology Foundation
Architectural Rationale & Trade-Offs
Evaluating failure modes, scaling bottlenecks, and defensive engineering decisions.
Why Redis Streams + PostgreSQL instead of Kafka?
Kafka introduces severe operational overhead for mid-stage startups (Zookeeper/KRaft clusters, partition rebalancing, consumer lag monitoring). Redis Streams delivers 100,000+ ops/sec throughput with minimal latency and negligible infrastructure footprint, while PostgreSQL guarantees financial transaction consistency.
How do you handle out-of-order events?
State transition guards with monotonic versioning. Each account entity maintains a `state_version` integer. If an event labeled `TRANSACTION_SETTLED` arrives before `TRANSACTION_INITIATED`, the event processor rejects the transition, requeues the event with a 500ms delay, and processes it only once the prerequisites are satisfied.
Where does caching live?
Idempotency cache lives in in-memory Redis with a 72-hour TTL. When an event arrives, Redis `SET idempotency:{eventId} PENDING EX 86400 NX` is called. If the key already exists, an instant HTTP 200 is returned without touching the database or triggering duplicate payment workflows.
What happens at 10x traffic spikes?
The edge ingestion gateway does zero database queries; it strictly validates signatures and pushes to the queue buffer in under 15ms. The buffer absorbs traffic surges gracefully, allowing downstream worker pools to process events at a controlled, sustainable rate without exhausting Postgres connection limits.
What happens if a worker crashes mid-transaction?
Redis Streams consumer groups track message acknowledgment (`XACK`). If a worker dies while processing a payload, the heartbeat monitors detect the idle consumer, and another worker automatically claims the message via `XCLAIM`.
What would I deliberately NOT build?
1) Synchronous database writes directly in webhook handlers. 2) Two-phase commit protocols across distributed databases. 3) Complex microservice meshes when a dedicated Fastify ingestion gateway and a worker pool can process 50 million events per day on a $150/mo server.
Project Horizon: High-Volume Cross-Border FinTech CRM & Webhook Automation Platform
22% Increased Conversion & 0% Lost Transactions across �50M+ volume
You own the system.
The code. The infra. The data.
Software should not become valuable enough to matter and then be impossible for the client to own or operate.
Everything I build is 100% client-owned intellectual property from day one. You own the code, the accounts, the infrastructure, and the data. No vendor lock-in.
What belongs to you in full:
- 01Source code & Complete Git Repositories
- 02Apple, Google & Enterprise Developer Accounts
- 03Cloud Infrastructure, VPCs & Production Databases
- 04Figma Design Files, Assets & Documentation
- 05CI/CD Deployment Pipelines & Signing Keys
Have a system that needs this level of architectural rigor?
Whether you are building from zero or rescuing a fragile prototype, I provide decisive architectural leadership.
Start an Architectural Engagement