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• Designed the backend architecture for core modules of a multi-tenant wealth-management platform using Node.js, NestJS and TypeScript; defined service boundaries, API contracts and domain models for CRM, investor portal and financial operations. • Evolved a unified API layer across GraphQL/Apollo and REST: designed schemas/resolvers and service-to-service endpoints, and standardized error models, versioning and Swagger/OpenAPI contracts. • Evolved the PostgreSQL schema with TypeORM and delivered 35+ schema/data migrations while preserving backward compatibility, data integrity and safe production rollout of changes. • Built event-driven processing on AWS SQS FIFO with idempotent consumers and guaranteed ordering; moved heavy workloads to Bull/Redis and AWS Lambda, adding CloudWatch observability, IAM controls and Secrets Manager. • Implemented financial domain logic including transaction state machines with audit trails, corporate actions/stock splits, realized P/L and portfolio metrics (CAGR, Sortino, drawdown), including edge cases and safe operation reprocessing. • Delivered integrations with Interactive Brokers, TwelveData and CoinMarketCap: market-data normalization, resilient error handling, correlation IDs, JWT/OTP, rate limiting and Jest integration tests; supported integrations in production.

• Designed a cloud-native backend on Node.js, Cloudflare and GCP: services on Cloud Run, asynchronous messaging through Pub/Sub, Cloud Storage/Cloud SQL, and separation of synchronous APIs from background workloads for independent scaling. • Implemented a real-time layer with WebSockets and Durable Objects, covering connection state, reconnect flows and lifecycle management; centralized secrets and production logging through GCP Secret Manager and Cloud Logging. • Designed the microservice core of an internal business-management platform with NestJS and DDD; defined bounded contexts and service contracts, used gRPC for synchronous calls, NATS for events and Redis cache-aside. • Took ownership of technical quality: ran code and architecture reviews, decomposed features, aligned technical decisions, mentored interns/junior developers and conducted technical interviews and live-coding sessions.

• Designed the backend of an automated repricing platform for Kaspi, Ozon, Halyk Market and Noon; separated marketplace adapters, pricing engine and ingestion into independent Node.js services so a single provider failure would not block other flows. • Built the Noon integration from scratch: reverse-engineered external APIs/catalog behavior, implemented scraping, ingestion and repricing rules, and normalized provider-specific data into a unified internal model for the seller dashboard. • Built a daily ETL/ingestion pipeline for ~2M products: decomposed crawling, parsing and persistence into Bull/Redis jobs and used MongoDB for the product catalog and seller snapshots. • Improved fault tolerance of external integrations under HTTP 429 responses, unstable payloads and temporary blocks using proxy/user-agent rotation, controlled retries, fail-safe jobs and audit logs for faster debugging. • Developed NestJS REST APIs and production delivery workflows using Docker, Bitbucket Pipelines, PM2 and environment configuration; handled production incidents, performed code reviews and onboarded new developers.

• Designed and implemented backend modules and REST APIs for an operational back-office system; moved business rules into the server-side layer and defined service contracts, DTOs and consistent validation rules for core workflows. • Implemented authentication/authorization and RBAC, request validation and centralized error handling; standardized secure communication between internal clients and backend APIs. • Designed API contracts and data flows with the frontend team, defining DTOs, error codes and operation lifecycles to eliminate client/server logic mismatches before production release. • Investigated production incidents at the API and data layers, performed root-cause analysis from logs and reproducible cases, and contributed to code reviews, task decomposition and release planning.