Radek Ostrowski, Developer in Brisbane City, Queensland, Australia

Radek Ostrowski

Ethereum Developer

Brisbane City, Queensland, Australia
Toptal Member Since
September 24, 2014

Radek is a certified Toptal blockchain engineer particularly interested in Ethereum and smart contracts. In the fiat world, he is experienced in big data and machine learning projects. He is a triple winner in two different international IBM Apache Spark competitions, co-creator of PlayStation 4's back end, a successful hackathon competitor, and speaker at conferences in Australia, Poland, and Serbia.

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Smart Contracts, Ethereum, Blockchain
British Asset – Kauri Crypto (via Toptal)
JavaScript, GRAPH, Truffle, Solidity, Ethereum
Zipmex Exchange (via Toptal)
Truffle, Solidity, Ethereum


Brisbane City, Queensland, Australia



Preferred Environment

GitHub, MacOS, Unix

The most amazing...

...achievement I've had is winning two international Apache Spark competitions run by IBM.

Work Experience

2018 - PRESENT

Blockchain Consultant

  • Engaged with clients wanting to enter the blockchain space, especially in the Ethereum ecosystem.
  • Won a prize for my "Time Locked Wallet" demo project in ConsenSys, a uPort Blockchain and Identity hackathon.
  • Designed and deployed smart contracts for tokens and ICOs including token vesting, refund vaults, and multi-signature wallets.
  • Performed smart contract security audits.
Technologies: Smart Contracts, Ethereum, Blockchain
2020 - 2020

Ethereum Engineer

British Asset – Kauri Crypto (via Toptal)
  • Created and deployed a staking contract for the platform token.
  • Created a demo DApp for the staking contract.
  • Implemented and deployed the graph for the staking contract tracking all events and allowing more advanced queries.
Technologies: JavaScript, GRAPH, Truffle, Solidity, Ethereum
2019 - 2020

Ethereum Engineer

Zipmex Exchange (via Toptal)
  • Created an upgradable erc20 token contract using a call delegate proxy.
  • Deployed the project to mainnet, verified on Etherscan, and provided instructions to the team on how to use it.
Technologies: Truffle, Solidity, Ethereum
2019 - 2019

Blockchain Engineer

LLPS, LLC (via Toptal)
  • Built a prototype of a real estate-backed loans platform.
  • Designed and built the Ethereum smart contracts forming the back end of the platform.
  • Created a user interface to the blockchain back end using React and Drizzle.
Technologies: Drizzle, React, DApps, Web 3.0, Solidity, Ethereum
2018 - 2018

Blockchain Engineer

Grayblock (via Toptal)
  • Helped to design and build a POC platform leveraging blockchain to improve electricity generation finance.
Technologies: DApps, Web 3.0, Solidity, Ethereum
2018 - 2018

Blockchain Engineer

IDEX – Aurora Labs S. A. (via Toptal)
  • Investigated various optimizations to Ethereum transaction throughput and gas cost for IDEX, currently the biggest on-chain exchange.
  • Prototyped several optimizations including scheduling and specialized smart contracts.
Technologies: Node.js, Solidity, Ethereum
2018 - 2018

Solidity Expert

Coinuma SL (via Toptal)
  • Helped to integrate Ethereum into the cryptocurrency exchange being built.
  • Demonstrated wallet generation, ether and token transfers, balance checks, and listening for events.
  • Advised on best security practices.
Technologies: Python, Web 3.0, Solidity, Ethereum
2018 - 2018

Blockchain Engineer

Fan Hero (via Toptal)
  • Provided consultancy on Ethereum.
  • Researched the use of permissioned blocks and IPFS.
  • Investigated transferring tokens without ether.
  • Prototyped a token contract.
Technologies: IPFS, Solidity, Ethereum
2018 - 2018

Ethereum/Solidity Developer

Kryptonex LLC (via Toptal)
  • Helped to integrate Ethereum and ER20 tokens into an exchange that is currently being built. It included address generation, token listing, and basic wallet operation related to ether and tokens using Web3.js.
Technologies: Web3.js, Ethereum, Solidity
2017 - 2018

Big Data Engineer

Commonwealth Bank of Australia
  • Provided consultancy on big data technologies and data science.
  • Architected and designed scalable solutions.
  • Developed solutions mainly with Apache Spark and Scala.
  • Employed machine learning techniques to maximize profit.
  • Led a team to victory in an internal hackathon—developed a Slack bot for knowledge discovery, deployed on AWS.
Technologies: Machine Learning, Scala, Apache Spark
2016 - 2016

Big Data Engineer

Taulia, Inc. (via Toptal)
  • Designed and built a new generation of Taulia’s data analytics platform.
  • Effectively processed financial data and extracted useful information both in batch and real time.
  • Built the platform in Scala, Spark Streaming and SQL, Cassandra, Kafka, Docker, and Redshift, running on Kubernetes on AWS.
Technologies: Amazon Web Services (AWS), Redshift, Kubernetes, Docker, Cassandra, Apache Kafka, Scala, Spark
2015 - 2016

Big Data Engineer

Method Mill
  • Helped integrate various data sources on a large scale.
  • Built a pipeline from MySQL to Amazon Redshift.
  • Created a syncing tool for Amazon S3.
Technologies: Amazon Web Services (AWS), MySQL, Amazon S3 (AWS S3), Redis, Redshift, Docker, Akka, Scala, Spark
2015 - 2015

Big Data Engineer

Max2, Inc. (via Toptal)
  • Helped design and build a community-powered venue discovery platform offering personalized recommendations, planning with friends, and curated and real-time information.
  • Used SparkSQL with DataFrames for data ingestion and Spark Streaming and MLlib for analytics.
  • Coded in Scala with Akka and Kafka and run on Mesos.
Technologies: Mesos, Akka, Apache Kafka, Scala, Spark
2015 - 2015

Senior Developer/Docker Evangelist

Tesco Bank
  • Introduced Docker to the development environment.
  • Helped improve the CI pipeline.
  • Extended the credit card portal.
  • Improved the user journey experience for a loan portal.
Technologies: Docker, Git, Cucumber, Spring, Java
2015 - 2015

Big Data Engineer

Expedia, Inc.
  • Helped to automate the build and run process.
  • Prototyped with Apache Spark.
  • Updated existing Hive and MapReduce workflows.
Technologies: Jenkins, Azkaban, Chef, Git, Apache Spark, Hadoop
2013 - 2015

Senior Software Developer/Team Leader

  • Built a production RESTful Java web service for Sony devices and platforms mainly for Sony PS4 and 4K-TV handling hundreds of thousands of transactions.
  • Developed on top of Spring Framework and Cassandra.
  • Offered authentication and authorization capabilities based on OAuth2.
  • Focused on quality of the code by employing unit testing with 100% code coverage, BDD with Cucumber, code reviews with GitHub pull requests, and Jenkins.
  • Produced a project collecting, analyzing, and visualizing statistics from Sony devices. The data is stored in Amazon S3 and processed using Hadoop (MapReduce and Hive). The data collection server and the BI portals are Java based (Spring MVC and REST). I secured the access to the web services (by extending Spring Security) and the relational databases. Other technologies used include Apache Karaf (OSGi) and Maven.
  • Worked on the “One Account – All Sony” global unified accounts integration project for Playstation and other devices.
  • Led a team of three in Brussels and collaborated closely with the rest of the team in San Diego.
Technologies: Splunk, GitHub, Jenkins, Amazon S3 (AWS S3), Amazon EC2, Apache Hive, Hadoop, OAuth 2, Cucumber, REST, Spring, Scala, Java
2012 - 2012

Senior Developer

DeltaDNA (GamesAnalytics)
  • Tackled the challenges of real-time data collection, predictive analytics, data measurement, and user engagement for the millions of online and mobile computer game sessions, personalizing the user’s gaming experience and increasing retention and revenue as a result through optimized game design and individually targeted in-game messaging.
  • Designed, developed, and provided continuous updates and enhancements of new features as part of an Agile in-house development team for the platforms and mobile SDKs.
Technologies: Amazon Web Services (AWS), iOS, Android, Apache Hive, Hadoop, VoltDB, REST, Spring, Java
2006 - 2012

Applications Consultant

EPCC (University of Edinburgh)
  • Led “Work Package 3: Test, Delivery, and Support” from start to finish in an Excellent-rated, data-intensive research project for the EU.
  • Designed and implemented the test platform, new software components based on Java, REST, Spring, Hibernate, and HDFS and extended existing software components such as OGSA-DAI during the lifespan of the project.
  • Worked on a master of science in high-performance computing, “test infecting” the students by lecturing and leading tutorials on unit testing and extreme programming and Agile methods; also created and gave a lecture on cloud use cases.
  • Developed a RESTful presentation layer based on Jersey for the software program OGSA-DAI.
  • Designed and developed an iPhone application for the UK National Supercomputing Service.
  • Fixed performance problems involving CUDA, C, JNI, and Java code and improved its graphical user interface via a spinout company.
  • Contributed to the project investigating the usage of Hadoop/MapReduce and clouds (Amazon EC2/Eucalyptus) for the analysis of post-genomic data.
  • Enabled the integration of the UKQCD community with the International Lattice Data Grid by implementing a web service layer in Java.
Technologies: Amazon Web Services (AWS), Hadoop, Spring, REST, Java


Topcoder/ConsenSys - uPort Blockchain and Identity Hackathon

Designed and implemented Ethereum dApp, which won a prize in the hackathon. It consists of smart contracts and a web front-end, and can be used for time locking Ethereum and ERC20 tokens. The dApp could be used for crypto gifts and vesting.

My Perfect Weather - IBM Spark Competition

I designed and built the web service that became a winner of the Grand Prize and the Fan Favourite award in the IBM Sparkathon.

Dipping into the Big Data River: Stream Analytics at Scale

I presented my project at the biggest data conference in Australia. Recorded talk is available here:

Kaggle - Data Science Competitions

My rankings demonstrate my ability to compete with the world's best data scientists:
* Top 6% (100/1984) in Expedia Hotel Recommendation
* Top 9% (84/979) in Outbrain Click Prediction

iWisps - IBM Spark Competition

A fast, scalable, and portable local business recommender microservice powered by Apache Spark. I designed and built the project that became a winner in the IBM Spark competition and received a 'big check' at the IBM event in NYC.

Scala for Data Science

I was a technical reviewer for the book.

Contributions to Spark Notebook

Created a demonstration of anomaly detection in Spark using Spark SQL, Spark Streaming, and MLlib.

Contributions to Stubby4j

Added functionality to serve files from the filesystem path based on the RegEx expression specified in the request.

Contributions to the Spring Security OAuth

Extended the expression methods to allow testing for existing scope by specifying a RegEx expression.
Image of Getting Started With Docker: Simplifying DevOps publication

Getting Started With Docker: Simplifying DevOps

Image of How I Used Apache Spark and Docker in a Hackathon to Build a Weather App publication

How I Used Apache Spark and Docker in a Hackathon to Build a Weather App

Image of Time-locked Wallets: An Introduction to Ethereum Smart Contracts publication

Time-locked Wallets: An Introduction to Ethereum Smart Contracts

Image of The Ultimate ENS and ĐApp Tutorial publication

The Ultimate ENS and ĐApp Tutorial

Image of Introduction to Apache Spark with Examples and Use Cases publication

Introduction to Apache Spark with Examples and Use Cases




Solidity, Scala, Java, Python, JavaScript


Truffle, Apache Spark, Play Framework, Spring, Hadoop, OAuth 2, Spark, Akka


Spark Streaming, Web3.js, Node.js, React, Drizzle


Git, Spark SQL, Cucumber, Jenkins, GitHub, Splunk, Chef, Mesos


Data Science, Agile Software Development, Functional Programming, Scrum, Kanban, REST


Android, Drupal, Blockchain, Ethereum, Docker, Linux, MacOS, Kubernetes, Hyperledger, R3 Corda, Apache Kafka, Amazon Web Services (AWS), Amazon EC2, iOS, Unix


NoSQL, Cassandra, Redshift, Apache Hive, Amazon S3 (AWS S3), VoltDB, Azkaban, Redis, MySQL


Ethereum Smart Contracts, Machine Learning, Data Engineering, Freelancing, Altcoin, Smart Contracts, IPFS, Web 3.0, DApps, GRAPH


2005 - 2006

Master of Science (with Distinction) Degree in High Performance Computing

University of Edinburgh - Edinburgh, UK

2004 - 2005

Bachelor of Science (with Honors) Degree in Computing

Edinburgh Napier University - Edinburgh, UK

2001 - 2004

Bachelor of Science Degree in Physics with IT

Nicolas Copernicus University - Torun, Poland



Architect Certification for Apache Cassandra



Developer Certification for Apache Spark



Java Web Services Certified Expert