Jakub Kozlowicz, Developer in Berlin, Germany
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Jakub Kozlowicz

Verified Expert  in Engineering

Back-end Developer

Berlin, Germany

Toptal member since December 23, 2021

Expertise
Back-end DevelopersAlgorithmsMultithreadingLinuxPythonSQLPostgreSQLDatabaseDockerGitKubernetesREST API
Bio

Jakub is a product-minded entrepreneur and software engineer with over nine years of experience, specializing in back-end and mobile development. He is seeking to leverage his professional expertise to provide high-quality services at any company and create an impact on customers.

Portfolio

Alemanzo GmbH
Python, iOS, Swift, SwiftUI, App Store, Google Cloud, Flask, FastAPI, MacOS...
Raffolux Ltd
Django, Python, Amazon Web Services (AWS), PostgreSQL, Amazon RDS, Docker...
Berlin-based Energy-as-a-Service Company
Python, Object-oriented Programming (OOP), IPC, Containerization, NoSQL...

Experience

  • Back-end Development - 9 years
  • Python - 9 years
  • Distributed Systems - 7 years
  • Kubernetes - 5 years
  • Cloud Computing - 5 years
  • Mobile Development - 2 years
  • SwiftUI - 2 years
  • iOS - 2 years

Availability

Full-time

Preferred Environment

MacOS, PyCharm, Xcode, Slack, Google Cloud, Terminal, Unix, Python, GitHub

The most amazing...

...thing I've recently worked on is an iOS app in the education sector, built with SwiftUI and powered by a Python back-end hosted in the GCP.

Work Experience

CEO and Founder

2020 - PRESENT
Alemanzo GmbH
  • Bootstrapped a company, designed, implemented, and shipped an iOS app to learn German. Built the app with SwiftUI, a website and admin panel using Flask and Vue, back-end APIs with Flask, FastAPI, and Google Cloud, and created content for it.
  • Hired and coordinated external translators to localize the app into eight languages, lawyers to write legal documents and register a trademark, and copywriters to write marketing a copy.
  • Ran all engineering efforts, maintained the whole stack, implemented new features, ran ad campaigns on Facebook Ads and Apple Search Ads, and continuously created and loaded new content.
  • Learned a brand new SwiftUI framework made by Apple, which I then applied to build a slick and complex mobile app, including auto-renewable subscriptions, user management, animations, cross-tab synchronization, and back-end communication.
  • Set up the infrastructure in Google Cloud, Kubernetes cluster, exposed the service to the internet, implemented a server to serve static files, and configured CDN and security checks. Made the deployment process easy, idempotent, and ready to scale.
Technologies: Python, iOS, Swift, SwiftUI, App Store, Google Cloud, Flask, FastAPI, MacOS, Vue, Localization, Software Engineering, Back-end Development, Mobile Development, Mobile Design, SQL, PostgreSQL, Figma, Docker, Product Design, Internationalization, Kubernetes, Google Kubernetes Engine (GKE), Cloud Computing, Algorithms, Git, Functional Programming, Software Architecture, JavaScript, GitHub, Deployment, Asynchronous Programming, Jinja, HTML, Databases, REST APIs, Back-end, REST, Bash, Architecture, Python 3, APIs, PyCharm, Terminal, Unix, Google Chrome, Distributed Systems, Entrepreneurship, Computer Science, CI/CD Pipelines, Debugging, Google Cloud Platform (GCP), Automation, SQLAlchemy, Pytest, Linux, Redis, DevOps, Microservices, Swagger, OpenAPI

Senior Python Developer

2023 - 2023
Raffolux Ltd
  • Audited the existing system, reported performance bottlenecks to the CEO, and advised on possible solutions.
  • Reduced page load time from five seconds to under one second by optimizing HTML templates per device type (web/mobile) and by introducing client-side rendering with React.
  • Created a setup for building and releasing new versions of React-powered front end.
  • Ran load tests and analyzed deployment setup to find infrastructure-related issues and ensure the website could sustain increased traffic.
Technologies: Django, Python, Amazon Web Services (AWS), PostgreSQL, Amazon RDS, Docker, Amazon EC2, React, AWS CloudFormation, Amazon S3 (AWS S3)

Python Developer

2022 - 2022
Berlin-based Energy-as-a-Service Company
  • Developed parts of a Python SDK for managing IoT devices to control assets used to produce renewable energy. Wrapped lower-level APIs with a clean and robust async Python code to make it easier for data scientists and customers to work with the SDK.
  • Explored edge cases for various topologies of electrical component graphs that the SDK can interact with, applied workarounds, and reported issues to be solved by the team.
  • Set up and implemented automated tests using GitHub Actions.
  • Build a small testing framework to mock async data sent by electrical components and test if the system behaves as expected.
Technologies: Python, Object-oriented Programming (OOP), IPC, Containerization, NoSQL, Distributed Systems, Async/Await, gRPC, GitHub, Pytest, Pandas, NumPy

Senior Python Developer

2022 - 2022
US-based Shipping Company (Toptal Client)
  • Migrated a Django-based app from Python 2/Django 1.6 to Python 3/Django 3.2: repaired 3,000+ tests, applied workarounds for deprecated libraries, and adjusted the code to the new Python syntax and new APIs.
  • Researched and executed the initial plan to migrate the project, created a playbook with common issues to be reused by other engineers, and devised a mechanism to measure the progress reported to management.
  • Onboarded and brought up to speed six additional engineers who joined the project.
Technologies: Python, Django, Django REST Framework, Docker, GitHub, Celery, Pytest, Python Asyncio, Linux, Amazon Web Services (AWS), Microservices, Swagger, OpenAPI

Software Engineer

2019 - 2020
Revolut
  • Maintained and repaired an old system for transaction monitoring and worked with product owners to re-architect and implement a new version of that system to sustain increasing traffic and provide features requested by other teams.
  • Integrated MaxMind IP intelligence into data warehouses leading to an increase in accuracy of risk calculations.
  • Streamlined workflows of data scientists by implementing and deploying ETL pipelines to extract data from production databases.
Technologies: Python, Kubernetes, Google Cloud, Google Kubernetes Engine (GKE), Unix, Slack, Jira, CI/CD Pipelines, Flask, Software Engineering, Back-end Development, SQL, PostgreSQL, Docker, Large Scale Distributed Systems, Cloud Computing, Algorithms, Git, Functional Programming, Software Architecture, Data Pipelines, Deployment, Databases, REST APIs, Back-end, REST, Bash, Architecture, Python 3, APIs, PyCharm, MacOS, Terminal, Google Chrome, Distributed Systems, Computer Science, Debugging, Asynchronous Programming, Google Cloud Platform (GCP), Automation, SQLAlchemy, Pytest, Python Asyncio, Linux, Pandas, Redis, DevOps, Microservices, Swagger, OpenAPI

Senior Software Engineer

2018 - 2019
Here Technologies
  • Developed parts of a Scala framework to run tests on large datasets to validate the quality of new versions of maps and catch regressions.
  • Created and operated AWS EMR clusters to test and run the framework and integrated the framework with the company’s CI/CD system.
  • Analyzed maps produced by other teams and applied the framework to run validation pipelines, which improved the quality of the maps and revealed regressions.
Technologies: Scala, Spark, Jenkins, CI/CD Pipelines, Maps, Software Engineering, Back-end Development, Docker, Large Scale Distributed Systems, Kubernetes, Cloud Computing, Algorithms, Git, Functional Programming, Software Architecture, Data Pipelines, Deployment, SSH, REST APIs, Back-end, Bash, Architecture, APIs, MacOS, Terminal, Unix, Google Chrome, Distributed Systems, Computer Science, Jira, Debugging, Automation, Linux, Amazon Web Services (AWS), DevOps

Software Engineer

2017 - 2018
Here Technologies
  • Developed parts of a Scala framework to run tests on large datasets to validate quality of new versions of maps and catch regressions.
  • Created and operated AWS EMR clusters to test and run the framework, integrated the framework with the company’s CI/CD system.
  • Analyzed maps produced by other teams and applied the framework to run validation pipelines, which improved the quality of the maps and revealed regressions.
Technologies: Scala, Spark, CI/CD Pipelines, Data Pipelines, Software Engineering, Back-end Development, Docker, Kubernetes, Cloud Computing, Algorithms, Git, Functional Programming, Software Architecture, Jenkins, Deployment, SSH, Back-end, Bash, Architecture, MacOS, Terminal, Unix, Google Chrome, Distributed Systems, Computer Science, Jira, Maps, Debugging, Automation, Linux, Amazon Web Services (AWS)

Software Engineer

2016 - 2017
Zalando SE
  • Maintained, troubleshot, and provided company-wide support with a system for data center deployments.
  • Engineered a migration from Stash to GitHub Enterprise and coordinated the migration for over 2,000 projects across the entire company.
  • Learned best practices of working in a multi-team environment, designing and developing good APIs, and deploying apps to AWS and an on-premises data center.
Technologies: Python, GitHub, GitHub API, Stash, Jira, Terminal, Debugging, Deployment, Software Engineering, Back-end Development, SQL, PostgreSQL, Docker, Cloud Computing, Algorithms, Git, Software Architecture, Jenkins, SSH, Databases, REST APIs, Back-end, REST, Bash, Architecture, Python 3, APIs, PyCharm, MacOS, Unix, Google Chrome, Distributed Systems, Computer Science, Large Scale Distributed Systems, Kubernetes, CI/CD Pipelines, Asynchronous Programming, Automation, SQLAlchemy, Pytest, Linux, Amazon Web Services (AWS), Microservices, Swagger, OpenAPI

Python Developer

2014 - 2015
Ypsilon.Net
  • Fixed bugs and implemented new features in the company’s flight search and aggregation engine for booking flights.
  • Designed and implemented a web UI based on XML schemas for interacting with the company's flight search engine and booking system, which supported over 70 API versions and was ready to support future changes in the API.
  • Promoted the web UI for interacting with the back-end APIs to engineers and product owners, which enabled quicker and easier testing of new features and served as a common interface between technical and non-technical teams.
  • Documented the technical onboarding process and created a guide that streamlined and facilitated the onboarding for new employees.
Technologies: Python, JavaScript, Backbone.js, Unix, Twisted, CSS, Asynchronous Programming, Software Engineering, Back-end Development, SQL, PostgreSQL, Algorithms, Git, SSH, Jinja, HTML, Databases, Back-end, Bash, PyCharm, Terminal, Google Chrome, Distributed Systems, Computer Science, Large Scale Distributed Systems, Jira, Debugging, Linux

Python Developer Trainee

2014 - 2014
Prime Capital
  • Developed a Python-based application for parsing Excel files with weekly portfolio recommendations from third-party providers. Turned simple mathematical models provided by analysts into code to be run on the data coming from the Excel sheets.
  • Built a web application based on the web2py framework to generate PDF invoices from Excel files, which reduced the number of errors done by two analysts and saved 5% of the time of each of them.
  • Taught analysts how to apply Python to process financial data to achieve a higher level of automation than by working solely with Excel files.
Technologies: Python, Anaconda, Software Engineering, Back-end Development, Algorithms, HTML, Databases, Back-end, PyCharm, Computer Science, Debugging

Python Developer Intern

2013 - 2013
Allegro
  • Developed a Django-based app for managing audits performed by company auditors, including CRUD operations and filtering and grouping of audits.
  • Created a web front-end for the audit management systems to enable auditors a quick and easy way to access and process the audit data. Used JavaScript libraries to implement graphs for tracking and visualizing audit progress.
  • Wrote puppet scripts to deploy the audit management system to the on-premises data center. Deployed and maintained the back end of the audit management system.
Technologies: Python, Django, Unix, SSH, Deployment, JavaScript, Software Engineering, Back-end Development, SQL, Algorithms, CSS, HTML, Databases, Back-end, Bash, PyCharm, Terminal, Google Chrome, Computer Science, Jira, Debugging, SQLAlchemy, Linux

Python Developer Intern

2012 - 2012
STXNext
  • Developed web applications using Python, Pylons, Flask, CSS, HTML, JavaScript, Mercurial Hg, and SQL.
  • Wrote unit and integration tests for a Python-based back end used to provide banking services for minors, such as tests for login flows, account browsing, and navigation within the service.
  • Created technical documentation for APIs of the banking system for minors. The APIs were implemented by colleagues and handed to me to create the documentation.
Technologies: Python, Jinja, HTML, Flask, JavaScript, Software Engineering, Back-end Development, Algorithms, Back-end, Bash, Unix, Terminal, Google Chrome, Computer Science, Jira, Debugging, SQLAlchemy, Linux

Experience

Alemanzo

https://www.alemanzo.com
Designed, implemented, and shipped an iOS app for learning the German language. Built the app with SwiftUI, a website and admin panel using Flask and Vue, back-end APIs with Flask, FastAPI, and Google Cloud, and created content for it.

Education

2013 - 2014

Master's Degree in Computer Science

Poznan University of Technology - Poznan, Poland

2009 - 2013

Bachelor's Degree in Computer Science

Poznan University of Technology - Poznan, Poland

Skills

Libraries/APIs

REST APIs, SQLAlchemy, OpenAPI, Asyncio, Vue, GitHub API, Python Asyncio, Scapy, Backbone.js, Pandas, NumPy, React

Tools

PyCharm, Xcode, Terminal, Git, GitHub, Pytest, Slack, Google Kubernetes Engine (GKE), Jira, Figma, Jenkins, Stash, Celery, AWS CloudFormation

Languages

Python, SQL, HTML, Bash, Python 3, Swift, JavaScript, Scala, CSS

Frameworks

Flask, SwiftUI, Jinja, Swagger, Twisted, Django, gRPC, Spark, Django REST Framework

Paradigms

Functional Programming, Asynchronous Programming, REST, Object-oriented Programming (OOP), Microservices, Mobile Development, Mobile Design, DevOps, Automation

Platforms

MacOS, Unix, Google Chrome, Docker, Kubernetes, Google Cloud Platform (GCP), Linux, iOS, Amazon Web Services (AWS), CrowdStrike, Anaconda, Amazon EC2

Storage

Google Cloud, PostgreSQL, Data Pipelines, Databases, Redis, NoSQL, Amazon S3 (AWS S3)

Other

Software Development, Distributed Systems, Computer Science, Localization, Software Engineering, Back-end Development, Internationalization, CI/CD Pipelines, Algorithms, Software Architecture, Debugging, APIs, Back-end, Architecture, Async/Await, Containerization, Multithreading, FastAPI, Entrepreneurship, App Store, Product Design, Large Scale Distributed Systems, Cloud Computing, Deployment, SSH, IPC, Web Scraping, Multiprocessing, Maps, Amazon RDS, Cybersecurity Operations

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