Mikael Marceniuk

Built and launched Dalua.top, an e-commerce store with customer accounts and Mercado Pago payments (Next.js, Drizzle, PostgreSQL, BetterAuth).

Built a Next.js landing page with English localization for Higher Up, a company with clients in Europe, the US and Japan; deployed on Vercel behind Cloudflare and optimized to load in about 1 second worldwide.

Designed the architecture of a multi-tenant scheduling platform as the primary developer (Java, Spring Boot, Hibernate, PostgreSQL, Flyway).

Ran a spike comparing database-per-tenant, schema-per-tenant and shared-schema strategies, and implemented schema-per-tenant isolation with Hibernate's CurrentTenantIdentifierResolver and MultiTenantConnectionProvider, keeping client data isolated on a single database.

Wrote integration tests that run CRUD operations against every table to validate manually provisioned tenant schemas before they go live.

Built automatic provider fallback for casino game integrations during the migration required by Brazil's 2024 betting regulation: when a provider was offline, requests were routed to the next available one, keeping games online. Also built a feature to manage providers dynamically.

Built a referral system end to end (Python + Next.js) in a two-person team, which drove around 10% revenue growth.

Monitored and validated platform features overnight during the migration of billions of records from the EU to Brazil.

Built and maintained daily automation jobs integrating 3 databases (PostgreSQL, SQL Server) with Lecom (BPM platform), DocuSign and Feedz (HR platform) via REST APIs, cutting one process from 4 days to 2 hours.

Built an asset management system (NestJS + Next.js) from scratch for an 8-person team, replacing two spreadsheets for tracking and history across 300+ assets; reports that took 2–3 days of manual consolidation now generate in under a minute.

Introduced unit and integration tests with Jest after repeated regressions whenever Lecom workflows were updated.

Joined an AB InBev project as the only fullstack developer on a 6-person team running a month behind schedule; delivered React + Express.js features that brought it back on track within a month.

Built, solo in 2 weeks, a pipeline importing millions of Excel rows into a relational database for a US manufacturing client, using AWS SQS for asynchronous batch processing so the API stayed responsive.

Deployed new microservices to Kubernetes and configured their networking alongside the tech lead.

Started as the only React Native developer in a 5-person company and moved to fullstack within a month.

Built a mobile inventory feature with QR code scanning and voice recognition for a large wholesale distributor, replacing manual stock counts.

Built a damage reporting system (React + Spring Boot on AWS) letting warehouse teams track incoming shipments and log damaged products with photos.

Set up the company's first CI/CD pipeline with Jenkins.