Marek L.
Senior Software Engineer
Experience
Sep 2024 - Sep 2025
1 year 1 monthPoland
Senior Software Engineer
Allegro
- Led a cross-functional squad (6–8 engineers + PM + designer) owning design → delivery → SLOs; shipped Go + Kotlin/Spring Boot services, Python ops tooling, Node.js utilities, and gRPC/REST contracts deployed on Kubernetes (GKE/EKS) with Istio ingress, Argo CD/Helm GitOps, and Prometheus/Grafana + OpenTelemetry dashboards.
- Built idempotent cart/checkout (Gomicroservices; gRPC/REST) with token-scoped retries and consistent hashing; p95 latency – 35%, auth errors –18%; cached reads via Redis and stored transactions in PostgreSQL; Kafka outbox guaranteed once-only effects.
- Migrated legacy endpoints using Strangler Fig + canary/blue-green on Kubernetes (GKE/EKS); controlled traffic with Istio (circuit breakers, rate limiting) and promoted via Argo CD/Helm; change-failure rate <5% with weekly release cadence; Prometheus/Grafana SLOs enforced.
- Orchestrated an event-driven order pipeline on Kafka (outbox/inbox, DLQ, replay tooling) with Go/Python consumers, gRPC/REST façades, Redis for idempotency keys, and PostgreSQL for durable state; duplicate shipments → near-zero; reconciliation hours → minutes.
- Implemented PSD2/3-D Secure and acquirer failover: Go gateway + Node.js/NestJS webhook handlers; Kafka events; Prometheus/Grafana SLO alerts; SCA success +12%, soft declines –8% without conversion loss.
- Peak-readiness: k6 tests, HPA/autoscaling on Kubernetes (GKE/EKS), chaos drills; Istio fault injection verified bulkheads; served 2.1× peak TPS with zero Sev-1 incidents.
- Observability-first: OpenTelemetry traces, RED/USE metrics, Prometheus/Grafana alerting; MTTR –30%, alert noise –40%; Argo CD/Helm rollbacks gated on SLO burn rates.
- Search/listing performance: Redis edge caching, feature-flagged ranking tweaks via Node.js control plane; session→add-to-cart +0.6 pp; Next.js/React internal surfaces with selective hydration improved Core Web Vitals (LCP –300 ms; CLS within budget).
- Returns & refunds: saga orchestration in Go with idempotent compensations; durable workflows in PostgreSQL; Kafka event choreography; RMA tickets –22%.
- Standardized CI/CD: GitHub Actions → Argo CD/Helm (GitOps), ephemeral PR envs on Kubernetes, Istio traffic-splits; lead time –25%, deploy success >95%.
- Mentored three engineers; led design reviews/hiring panel; authored runbooks/post-mortems adopted by two sister teams.
- Front-of-site interfaces & tooling: React, Next.js, Angular, Vue.js for ops consoles and internal storefront modules; backend admin tools in Python (FastAPI/Django) and Node.js (NestJS).
Jan 2017 - Aug 2024
7 years 8 monthsPoland
Full Stack Developer
- Built and maintained internal enterprise systems used by over 1,000 wholesale partners, streamlining operations for apparel distribution and order processing.
- Developed and maintained full stack internal platforms using React (frontend), Node.js (Express) and Python (FastAPI) for warehouse management and partner operations, reducing manual workflows by 60%.
- Migrated legacy .NET apps to a React + Next.js frontend integrated with NestJS and Django-based APIs, improving system reliability and cutting feature delivery time by 40%.
- Architected microservices for order processing and inventory control using Python (Django, FastAPI) and Node.js, deployed on AWS ECS with Fargate, enabling auto-scaling and zero-downtime deployments.
- Implemented user dashboards and admin panels with React, pulling data from REST and GraphQL APIs built with Node.js and secured with JWT-based auth via AWS Cognito.
- Leveraged AWS Lambda, S3, and API Gateway to build a document management feature for invoices and product assets, improving upload speed and reducing infrastructure costs by 25%.
- Built a real-time inventory sync pipeline using Python, PostgreSQL, Redis, and AWS SNS/SQS, improving stock update latency by 50% across partner systems.
- Designed and integrated CI/CD pipelines using GitHub Actions for frontend (React) and backend (Node/Python), including Cypress/Jest/Pytest testing and Docker-based deployment workflows.
- Monitored application health using New Relic, CloudWatch, and custom metrics from backend services, reducing MTTR for production issues by 45%.
Aug 2015 - Dec 2017
2 years 5 monthsFreelance Software Engineer
Confidential
- Developed responsive web components using HTML5, CSS3, and JavaScript, increasing session duration by 20% on client sites.
- Built scalable REST API development in Node.js and PHP, improving throughput and latency by 35%.
- Independently implemented token-based algorithms for user session tracking and custom search indexing, which reduced data retrieval time by 30%.
- Built real-time chat features with WebSocket, boosting engagement metrics by 25%.
- Contributed to mobile development using Ionic and Cordova for iOS and Android platforms.
- Integrated Stripe and PayPal into eCommerce flow, increasing transaction completion rate by 18%.
- Participated in bi-weekly Agile sprints by estimating stories, resolving tickets, and reducing backlog incidents by 40%.
- Authored unit tests and automated browser tests using Selenium, enhancing regression coverage.
- Led internal training sessions and authored documentation for onboarding new junior engineers.
Summary
Versatile, results-driven Senior Software Engineer with 10+ years of experience architecting and delivering scalable, secure full stack applications. Highly proficient in React, Node.js, Python, and AWS. Known for solving complex technical problems, optimizing performance, and fostering cross-functional collaboration from idea to launch.
Languages
Polish
NativeEnglish
AdvancedEducation
Aug 2011 - Jun 2015
National Louis University
Bachelor of Computing · Computer Science · Poland
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