Slaven Ostojić.

About

slaven.jpg

Software engineer with more than 10 years of professional experience in designing, building and scaling distributed systems, microservice platforms, and high-availability enterprise solutions.

Proven track record in leading engineering teams, driving architectural modernization, and delivering mission-critical systems in telecommunications, healthcare, finance, and large-scale consumer domains.

Passionate about software design and architecture, enjoy writing clean and well-tested code.

Active in local community, equipped with strong communication and leadership skills.

In love with my guitars, vinyl records, nature, snowboarding and chess.


Experience

Salt Square, Tuzla » Staff software engineer

November 2024 – Present

  • Architecting and designing a large-scale treatment-booking platform for North America’s #1 medical aesthetics provider, enabling major digital transformation initiatives.
  • Collaborating closely with product owners and business stakeholders, gathering requirements, preparing design proposals, and performing architectural reviews.
  • Leading a cross-functional team of 6 developers, driving engineering quality, reliability, and delivery throughput.
  • Designing foundational components of an AWS-hosted microservice ecosystem.
  • Integrating with Salesforce APEX and SOQL APIs to synchronize operational, booking, and customer data.
  • Implementing distributed scheduling, synchronization, and locking mechanisms in PostgreSQL (distributed locks, non-blocking consumers, event-driven reporting).
  • Implementing CI/CD pipelines with GitHub Actions, setting up automated deployments, QA workflows, and continuous monitoring with New Relic.
  • Documenting architecture using C4 diagrams for clear system understanding across teams.
Node.js
TypeScript
NestJS

ZIRA, Tuzla » System architect

May 2023 - November 2024

  • Designing microservice-based, distributed enterprise solutions for the leading telecommunications provider in Saudi Arabia.
  • Architecting and improving an electronic invoicing system integrated with ZATCA; optimized validation times by 100x via automation and redesign.
  • Designing marketplace integrations connecting suppliers, customers, and internal systems over TMF APIs.
  • Leading the development team responsible for end-to-end delivery of mission-critical components.
  • Creating internal tools to improve system maintenance, reduce operational overhead, and enhance reporting capabilities.
  • Designing and maintaining CI/CD pipelines using GitLab CI/CD.
Java/Spring Boot
Python

Salt Square, Tuzla » Senior software engineer

March 2022 - May 2023

  • Designed and developed large-scale, full-stack solutions for multiple clients, spanning backend, frontend, databases, and infrastructure.
  • Architected and implemented a central consumer portal for a leading domestic appliances company.
  • Designed and developed a feature flag service with advanced rule logic for a healthcare use case.
  • Owned multiple features within a HIPAA-compliant COVID testing platform in the US healthcare sector.
  • Built an inventory register integrating Google SSO.
  • Developed AWS-deployed web scrapers using Terraform IaC.
  • Mentored junior engineers on Spring Boot and unit testing best practices.
Java/Spring Boot
Python/FastAPI
Node.js/Next.js
React/Redux

Infobip, Tuzla » Software engineer

April 2019 - February 2022

  • Built distributed, data-intensive microservices ensuring high availability, geo-redundancy, and strict security requirements.
  • Developed Mobile Number Portability (MNP) systems that aggregated raw data from FTP, SFTP, HTTP, HTML, email, S3, and other sources into unified datasets for high-volume reads.
  • Improved the USSD platform supporting 3M+ concurrent sessions across Africa.
  • Designed and delivered a Voice Bot solution with DTMF support, ensuring end-to-end testing coverage.
  • Analyzed and redesigned the Email platform to support 10× increased traffic.
  • Organized and led the company’s internship program; mentored junior colleagues.
Java/Spring Boot
Python/Flask
Node.js/Express.js
Angular

Marvelsoft, Tuzla » Senior software developer

September 2014 - March 2019

  • Developed high-performance, multi-threaded, event-driven trading systems used across European and Asian markets.
  • Designed a real-time order management system for live order monitoring and performance analytics.
  • Improved and modularized a complex legacy system to support plugin-based extensions for external OMS platforms.
  • Built FIX gateways and feed handlers supporting multiple market data sources.
  • Served as project lead: defined requirements, coordinated development cycles, prioritized tasks, and communicated with clients.
  • Served as team lead: mentored developers, tracked progress, and provided technical coaching.
C++
Python
TypeScript

Technologies

Programming Languages

  • Java, JavaScript/TypeScript, Python, C++

Frameworks & Libraries

  • Java: Spring Boot, Hibernate
  • JavaScript/TypeScript: Node.js, Express.js, Next.js, React, Redux, Angular
  • Python: Flask, FastAPI, asyncio
  • C++: C++ Actor Framework

Testing Tools

  • JUnit/Jupiter, Mockito, Jest, Cypress, unittest

Databases & Caching

  • PostgreSQL, Oracle, MongoDB, Redis, Hazelcast

Messaging & Streaming

  • Kafka, ActiveMQ Artemis

DevOps & CI/CD

  • Docker, Kubernetes, Terraform, Jenkins, Git, GitHub Actions, GitLab CI/CD, AWS

Monitoring & Observability

  • Prometheus, Grafana, New Relic

Systems & Scripting

  • Linux, Bash

Telecommunications

  • Asterisk, FreeSWITCH

Other Activities

Agora center, Tuzla » Volunteer, teacher, trainer, mentor

March 2013 - Present


University of Tuzla, Tuzla » Developer / Contractor

February 2021 - December 2021

  • Developing tool for quality estimation at the university
  • Defining requirements and scope of the project, working on front-end and back-end sides, deploying and maintaining the complete solution

Faculty of electrical engineering, Tuzla » Teacher assistant

September 2018 - September 2021

  • Courses: Data structures and Web design (HTML, CSS and JavaScript)

Pecivo & Kafa, Tuzla » Coffee shop co-owner

February 2016 - November 2016


Education

Faculty of electrical engineering, Tuzla » Master’s degree - Computer Science

September 2018 - Present


Faculty of electrical engineering » Bachelor’s degree - Computer Science

September 2010 - September 2014


Portfolio

For more technical context on me please check my side projects. Most of them are not production ready. All of them are implemented in my free time to explore some concepts or to solve my real-life problems.

Quoter

Simple service for generating random quotes deployed using k8s. Quoter uses ChatGPT and RAG under the hood to generate answers with quotes inside.

Java
Spring Boot
Spring AI
PostgreSQL
OpenAPI
ChatGPT
RAG
Kubernetes
Docker


Pikajia

In Bosnia and Herzegovina we had PIK.ba online marketplace. It was a very primitive and limited marketplace but that is the place where I found the biggest number of my vinyl records. PIK did not have any advanced filters, especially no mechanism to subscribe on changes in filter results. I decided to help myself and developed Pikajia. Pikajia was deployed in AWS (ECR, IAM, Lambda, SQS, S3 and DynamoDB) using Terraform. In the meantime, OLX bought PIK and redesigned the site completely, introducing smart filters and update notifications. Pikajia is now out of service. RIP.

Python
Node.js
TypeScript
AWS
AWS CLI
Terraform
PlantUML
Structurizr (C4)
Bash


Market Agila

My main goal here was to try ksqlDB for tracking changes in the database with the possibility of ETL processing.

Java
Spring Boot
Kafka
Kafka Connect
Debezium
ksqlDB
PostgreSQL
Flyway
WebSocket


Fogg Boutique

I've started this project in order to try async Python and MongoDB change streams. Nice thing about this project is the fact that MongoDB is started as a replica set with a single node, since change streams require replica sets.

Python
FastAPI
asyncio
React
Axios
WebSocket
MongoDB
JWT


Stella

This project demonstrates usage of mentioned technologies to provide telemetry and observability mechanisms.

Java
Spring Boot
Prometheus
Grafana
Loki
Fluent Bit
Docker