Marek L.
Senior Software Engineer
Experience
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 (Go microservices; 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).
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%.
Freelance 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.
Skills
Frontend (Apps & Internal Tools): React 18, Next.js (Ssr/isr), Typescript, Vite/webpack, Redux Toolkit/zustand, React Query, Formik/react Hook Form, Tailwindcss, Css Modules/scss, Storybook, Shadcn/ui, Radix Ui, Headless Ui, Charting (Recharts, D3, Visx), React Flow, I18n (React-i18next), Accessibility (Wcag/aria), Core Web Vitals (Lcp/cls/inp), Code-splitting/lazy Loading
Backend & Apis: Python (Fastapi, Django), Node.js (Nestjs/express), Go; Rest & Graphql (Apollo/graphene), Grpc, Websockets/sse, Schema Validation (Pydantic/zod), Rate Limiting, Idempotency
Cloud & Devops: Aws (Ecs/fargate, Lambda, S3, Api Gateway, Cloudfront, Cognito), Gcp (Gke, Gcs, Bigquery), Docker, Kubernetes, Terraform/iac, Github Actions, Argo Cd (Gitops), Helm, Feature Flags (Unleash/flagsmith)
Data & Messaging: Postgresql, Mysql, Redis, Kafka/rabbitmq (Dlq/retries/outbox), Etl/elt, Dbt Basics, Indexing/partitioning, Performance Tuning
Observability & Reliability: Opentelemetry, Prometheus/grafana, Elk/opensearch, Slos/slis, Red/use, Canary/blue-green, Chaos/drills, Incident Response (Mttr↓)
Security & Compliance: Oauth2/oidc, Jwt/sso/2fa, Hmac Signatures, Tls, Secrets Management, Least Privilege, Gdpr; Hipaa-aligned Handling For Intake/marketing Systems
Architecture & Patterns: Microservices, Event-driven Design, Cqrs, Saga, Strangler Fig, Api Gateway, Circuit Breakers/bulkheads, Ddd-inspired Boundaries
Delivery & Ways Of Working: Agile/scrum/kanban, Pr Workflows, Trunk-based/gitflow, Preview Envs, Runbooks/post-mortems, Mentoring/hiring, Stakeholder Communication
Domains: E-commerce (Checkout/payments/fulfillment), Platform Engineering, Analytics/data Platforms, Healthcare Intake/marketing
Languages
Education
National Louis University
Bachelor of Computing in Computer Science · Computer Science · Poland
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