Hrvoje Grdic

Ruby on Rails & React Engineer · Tech Lead · Payments & Fintech

Zagreb, Croatia · Remote (EU & US overlap) · hrvoje.grdic1@gmail.com · back-slash.hr · github.com/caphg

Software engineer since 2011, contracting since 2014 through my own consultancy. I build and operate systems where money moves and mistakes are expensive: payment processing, billing, reconciliation and large-scale third-party integration. Usually the single point of technical ownership: architecture, implementation, AWS infrastructure, deploys and on-call, end to end.

Experience

Backslash d.o.o., Founder & Principal Engineer

2014 – Present

Independent software consultancy in Zagreb, delivering long-running engagements for clients in payments, e-commerce and SaaS. Member of the Toptal network, whose screening process admits roughly the top 3% of applicants.

RunPayments, Tech Lead

Mar 2023 – Present

Payment processing platform · Ruby on Rails, React, AWS

Technical lead and sole owner of a production payment processing platform: data model, application, front end, infrastructure and release process.
Engineered for correctness under money-movement constraints: idempotent transaction handling, reconciliation, auditable state transitions, and backwards-compatible, non-destructive migrations.
Run the entire AWS estate single-handedly (networking, compute, RDS, caching, object storage, IAM, monitoring and alerting), with zero-downtime deploys and rehearsed rollback paths.
Built the React operator and merchant surfaces on top of the Rails API.
Operate a multi-database platform, PostgreSQL on RDS alongside Oracle, with the Oracle side containerised in Docker so tests run against a reproducible local instance.
Single point of accountability for uptime: on-call, incident response, capacity planning and infrastructure cost.

Hubstaff, Senior Engineer

Jan 2020 – Feb 2023

Time tracking, payroll & invoicing SaaS · Ruby on Rails, Vue.js

Owned the integrations platform: roughly 30 third-party integrations across project management, accounting and payment providers, keeping time-tracking, project and payment data continuously in sync.
Designed sync to survive the real world: rate limits, partial failures, backfills, webhook-plus-polling hybrids, and constant upstream API drift across dozens of independent vendors.
Worked across the payroll and invoicing paths, where sync errors surface directly as incorrect payments.
Full-stack delivery in Rails and Vue.js on a large, long-lived production codebase.

Capitalize, Founding Engineer (sole)

2018 – 2019

Fintech startup · Ruby on Rails, React

Sole engineer alongside the founder. Built the entire product from zero: architecture, backend, front end, infrastructure and deployment.
The product I built solo carried the company through its $2M Series A; an in-house team was hired after the raise, and the product remains in operation today.

Client engagements via Toptal

2014 – 2018

US and EU clients · Ruby on Rails, Node.js, React, Android

Back-to-back contract delivery across payments, e-commerce, retail and mobile, for clients ranging from early-stage startups to household-name platforms. Highlights listed below.

Selected Client Engagements

BigCommerce

Real-time Rails sync engine holding items, orders, customers and payments consistent across BigCommerce, Square and Clover. Background-job architecture built around ordering guarantees, retries and idempotency.

Digital signage network

Rails platform for an advertising company running screens across hotels and venues: central ad management and per-display playlist scheduling. Held a contractual 7-minute publishing deadline on large playlists by sharding work across AWS Lambda with Redis caching, packaging Lambda code as Docker images and splitting live traffic across EC2 and Lambda behind an ALB with weighted routing.

Clover

Android applications for the Clover merchant device ecosystem, including native bridges between Android and Clover's SDK, and hybrid Ionic / Cordova integrations.

US sandwich franchise

Customer ordering application with deep Clover integration: kitchen and customer-facing receipt printing, plus a loyalty programme. Chain name under NDA.

Western Union

Node.js and Android development for customer-operated self-service terminals.

Philips

Large JavaScript ordering application for an apparel catalogue.

Boating in Boston

Ruby on Rails and Angular.js web application.

Griot

React Native and Android application built around real-time voice and video calling between field workers and remote support.

Also

20+ further engagements across payments, e-commerce and SaaS since 2014.

Open Source

treblle-ruby

Author of the official Treblle SDK for Ruby: Rails middleware reporting API requests, responses and errors to Treblle's monitoring platform, while keeping sensitive fields out of what leaves the application. MIT licensed · github.com/Treblle/treblle-ruby

Earlier Experience

Ericsson, Software Engineer

2013 – 2014

Telecommunications · Java

PBZ (Privredna banka Zagreb), Software Engineer

2012 – 2013

Banking · Java

One of Croatia's largest banks, and the start of a career-long specialisation in financial software.

Iskon Internet, Software Engineer

2011 – 2012

Internet service provider · Hrvatski Telekom group

Technical Skills

Backend: Ruby on Rails, Ruby, Python (Django), Node.js, REST & webhook API design, background-job architecture
Frontend: React, Vue.js, Angular.js, JavaScript
Mobile: Android (Java), React Native, Clover SDK & native bridges, Ionic, Cordova
Infrastructure: AWS (EC2, Lambda, RDS, S3, VPC, IAM, CloudWatch, ALB), Heroku, Vercel
Deployment: Docker, containerised services and Lambda images, ALB weighted routing, autoscaling, zero-downtime releases, monitoring & on-call
Testing & Perf: RSpec, Jest, Faker, DatabaseCleaner, performance profiling, memory and query analysis, production debugging
Data & Caching: PostgreSQL (RDS), Oracle, MySQL, Redis, Memcached, queueing and job pipelines
Domain: Payment processing, billing & invoicing, reconciliation, idempotency & consistency, third-party integration at scale

Education

MSc, Computing

Zagreb, Croatia

University of Zagreb, Faculty of Electrical Engineering and Computing (FER)