Marek L.-Senior Software Engineer
Check rate
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.
Industry experience
See where this freelancer has spent most of their professional time.
Experienced in Retail and Information Technology.
Business area experience
See which departments and functions this freelancer has contributed to most.
Experienced in Information Technology, Operations, Product Development, and Quality Assurance.
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
Statistics
Experience
Global experience
Expertise
Qualifications
Profile
Frequently asked questions
Have questions? Find more information here.
Marek is based in Kraków, Poland.
Marek speaks the following languages: Polish (Native), English (Advanced).
Marek has at least 10 years of experience. During this time, Marek has worked in at least 3 different roles and for 3 different companies. The average length of individual experience is 3 years and 4 months. Note that Marek may not have shared all experience and actually has more experience.
Based on recent experience, Marek would be well-suited for roles such as: Senior Software Engineer, Full Stack Developer, Freelance Software Engineer.
Marek's most recent position is Senior Software Engineer at Allegro.
In recent years, Marek has worked for Allegro and Google.
Marek is most experienced in industries like Retail and Information Technology.
Marek is most experienced in business areas like Information Technology, Operations, and Product Development. Marek also has some experience in Quality Assurance.
Marek has recently worked in industries like Retail.
Marek has recently worked in business areas like Information Technology, Operations, and Product Development.
Marek holds a Bachelor in Computer Science from National Louis University.
The availability of Marek needs to be confirmed.
Daily rate distribution
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Calculated based on our freelancers’ daily rates as of 7 Sep 2026. Actual rates may vary depending on seniority level, experience, skill specialization, project complexity, and engagement length.
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