Theodoros Goulas, Developer in Athens, Central Athens Regional Unit, Greece
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Theodoros Goulas

Verified Expert  in Engineering

Software Developer

Athens, Central Athens Regional Unit, Greece

Toptal member since October 26, 2022

Bio

Theodoros is a software engineer with over 7 years of experience as a back-end and full-stack developer. He specializes in cloud engineering and machine learning applications with a strong web app development background in the financial industry. Theodoros has studied computer science at the National Technical University of Athens and has obtained a master's degree in machine learning and artificial intelligence from the National Center for Scientific Research "Demokritos."

Portfolio

National Center for Atmospheric Research - General
Groovy, Grails, Back-end, MySQL, Elasticsearch, React, GitHub, Full-stack
PaymentComponents
Python 3, LangChain, JavaScript, Node.js, Pulumi, Amazon API Gateway...
Pierre Rappolt
Python, Python API, APIs, Pandas, Asyncio, Pytest, REST...

Experience

  • Java - 6 years
  • Microsoft SQL Server - 6 years
  • Software Deployment - 6 years
  • Python - 4 years
  • Docker - 3 years
  • Amazon Web Services (AWS) - 3 years
  • Machine Learning - 2 years
  • Jenkins Pipeline - 2 years

Availability

Part-time

Preferred Environment

Windows, PyCharm, IntelliJ IDEA

The most amazing...

...app I've developed is a prototype integrated with AWS that extracts data from financial messages and produces statistical metadata and ML insights.

Work Experience

[Phase 2] [Toptal Teams] Back-end developer for a Data Services Dashboard Redesign

2024 - PRESENT
National Center for Atmospheric Research - General
  • Redesigned the application dashboard using React with an Elasticsearch integration, optimizing the indexing capabilities.
  • Created a set of API services, enabling communication between the font-end React application and the Elasticsearch index.
  • Created the migration and data ingestion process from the existing MySQL database to the Elasticsearch index.
Technologies: Groovy, Grails, Back-end, MySQL, Elasticsearch, React, GitHub, Full-stack

Technical Lead

2021 - PRESENT
PaymentComponents
  • Developed a multi-platform solution using LLMs (OpenAI, Llama, Mistral) with LangChain, allowing users to query large document corpora and databases, retrieve results, generate plots, and perform advanced data analyses.
  • Implemented a set of API services designed as multi-agent processes for communication with LLMs via LangChain. Features include retrieval-augmented generation (RAG), natural language-to-SQL conversion, and code generation.
  • Built the application as a modular solution to support on-premise installations via Docker containers and AWS-hosted serverless architecture (Lambda, Cognito, S3, Step Functions, RDS), using the Pulumi framework.
  • Implemented a CI/CD pipeline with AWS CodePipeline and Git integration for automated build and test. Used Pulumi TypeScript scripts for AWS resource provisioning, built Docker images, and pushed them to Amazon ECR.
Technologies: Python 3, LangChain, JavaScript, Node.js, Pulumi, Amazon API Gateway, Lambda Functions, Docker, Amazon Elastic Container Registry (ECR), AWS Step Functions, AI Agents, React, React Native, AWS Glue, Data Modeling, Data Pipelines, ETL Tools, Django, Django REST Framework, GitHub, Full-stack, Amazon Cognito

Junior Python Developer | SaaS Company

2022 - 2023
Pierre Rappolt
  • Integrated the application with the Google, Zoom, Jamf, and Okta APIs.
  • Refactored the code by extracting a set of interfaces and classes, increasing the reusability and reducing the maintenance effort. As a result, the import process of the new API integration into the application was simplified drastically.
  • Implemented unit tests per API integration using the Python unittest and asyncio libraries.
Technologies: Python, Python API, APIs, Pandas, Asyncio, Pytest, REST, Object-relational Mapping (ORM), SaaS, SQLAlchemy, Protocol Buffers, FastAPI, Web Services, Django, Django REST Framework, GitHub

Full-stack Software Engineer

2019 - 2021
PaymentComponents
  • Designed, developed, and provided operational support in large-scale web applications for Cardlink, Greece's largest card acceptance network.
  • Built an extensive set of batch processes handling Cardlink's bank and merchant billing processes.
  • Performed development tasks in an account aggregator application that provides fintech and payment institutions a unified way to connect with banks, incorporating batch processes and web connection using API calls through the PSD2 protocol.
Technologies: Java 8, Spring 5, Spring Boot, React, Node.js, Jenkins Pipeline, Nexus, Azure, Microsoft SQL Server, Docker, Apache Tomcat, NGINX, LDAP, Java, Windows, APIs, Web Development, SQL, Back-end, Back-end Development, Microservices, Algorithms, Databases, Spring, Hibernate, REST APIs, Linux, Continuous Integration (CI), Git, Docker Compose, JavaScript, CSS, HTML, API Integration, CI/CD Pipelines, Elasticsearch, REST, Fintech, TypeScript, Object-relational Mapping (ORM), SaaS, Full-stack, Redux, Microsoft Azure, jQuery, Groovy, Grails, Web Services, React Native, GitHub, Next.js, Tailwind CSS

Software Engineer

2017 - 2019
Cognity
  • Assisted as a team member in developing an EPOS application for Vivacom, the largest telecommunications company in Bulgaria.
  • Redesigned and transformed the monolithic Java 6 Vivacom EPOS application into a modern system with a Java 8 microservices back end and a React and Node.js front end.
  • Collaborated in every step of the application's lifecycle, including design, development, deployment, continuous integration, and operational support.
Technologies: Java 8, Microservices Architecture, Spring 5, Spring Boot, JavaScript, React, Java, Docker, Windows, APIs, Web Development, SQL, Back-end, Back-end Development, Microservices, Algorithms, Databases, Spring, Hibernate, REST APIs, Git, Docker Compose, MySQL, HTML, API Integration, REST, Object-relational Mapping (ORM), Angular, Full-stack, Oracle, jQuery, Web Services, GitHub, Next.js

Experience

Explainable Multivariational Anomaly Detection Model

https://github.com/teogoulas/explainable-multivariational-anomaly-detection
I developed a deep learning model that performs anomaly detection on tabular and unstructured data or text extracted from financial messages under ISO 20022. The model uses variational autoencoder architecture to detect anomalies and the SHAP model to determine the key factors that explain the model's decisions. The application is built and integrated with the AWS platform (Amazon SageMaker).

Cardlink Apollo Web Application

https://apollo.cardlink.gr/login#en
I built a BI web application for customers of Cardlink, Greece's largest card acceptance network. I was mainly assigned back-end development tasks, incorporating Spring Framework microservices for Java 8. I also handled some front-end tasks in React and Node.js, mostly regarding the integration with external services, enabling the payment process using the PSD2 protocol.

Finaplo.AI

https://www.paymentcomponents.com/finaplo-ai/
A multitenant cloud application built on the AWS cloud platform can parse financial messages, such as SWIFT MT, ISO 20022, and SEPA, etc., and provide AI and ML metadata analysis of extracted data. This application consists of two distinct components: admin application and tenant application. The admin app is hosted in the management AWS account and handles tenants' onboarding, retention, monitoring, and billing processes. The tenant application is hosted in separate AWS accounts under the same organization. It receives bulk and real-time financial messages and provides ML insights and BI tools for statistics, KPIs, visualizations, and reports using Amazon ML services, SageMaker for forecast and anomaly detection, and external frameworks like GraphSAGE and a graph neural network for fraud detection.

Cardlink Admin Portal

https://mrchnt.cardlink.gr/
A large-scale custom web application that handles user management and billing processes of Cardlink, Greece's largest card acceptance network. I implemented a set of RESTful APIs based on the Spring Boot framework and batch processes handling Cardlink's billing processes.

Education

2020 - 2022

Master's Degree in Artificial Intelligence and Machine Learning

University of Pireaus - Pireaus, Greece

2011 - 2016

Master's Degree in Computer Science

National Technical University of Athens - Athens, Greece

Skills

Libraries/APIs

React, Node.js, REST APIs, PyTorch, TensorFlow, Pandas, jQuery, Jenkins Pipeline, Amazon EC2 API, Python API, Asyncio, SQLAlchemy, AMQP

Tools

PyCharm, IntelliJ IDEA, GitLab, Git, GitHub, Amazon SageMaker, Apache Tomcat, Jenkins, Docker Compose, Pytest, Amazon Simple Queue Service (SQS), Amazon Cognito, NGINX, AMQP-Processing, AWS CloudFormation, Amazon Elastic Container Registry (ECR), AWS Step Functions, AWS Glue

Languages

Python, Java 8, Java, SQL, Groovy, JavaScript, CSS, HTML, Python 3, TypeScript

Frameworks

Spring 5, Spring Boot, Spring Microservice, Spring, Hibernate, React Native, Django, Redux, Grails, Next.js, Angular, Thymeleaf, JUnit, Spring Batch, Django REST Framework, Tailwind CSS

Paradigms

Microservices Architecture, Microservices, REST, Continuous Integration (CI), Serverless Architecture, ETL, Object-relational Mapping (ORM), Unit Testing

Storage

Microsoft SQL Server, Databases, PostgreSQL, MySQL, Elasticsearch, Amazon DynamoDB, NoSQL, Data Pipelines

Platforms

Windows, Amazon Web Services (AWS), Docker, Linux, AWS Lambda, Nexus, Azure, Visual Studio Code (VS Code), Oracle, DigitalOcean

Other

APIs, Back-end, Back-end Development, Full-stack, Web Services, Computer Science, Software Deployment, Web Development, Algorithms, Cloud, API Integration, CI/CD Pipelines, Infrastructure as Code (IaC), Amazon RDS, Fintech, Data Processing, Data Engineering, SaaS, FastAPI, ETL Tools, Electrical Engineering, Machine Learning, Data Science, Computer Vision, Artificial Intelligence (AI), LDAP, Serverless, AWS Auto Scaling, Data Warehousing, Protocol Buffers, Microsoft Azure, State Machines, Amazon API Gateway, Integration Testing, Cloud Applications, LangChain, Pulumi, Lambda Functions, AI Agents, Data Modeling

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