Charis Nikolaidis - Full-Stack Engineer in Athens

Career 💡

For me, technology isn't just work.. it's an ongoing experiment where new frameworks appear faster than I can reject them, and best practices change right after I finally convince juniors to follow them. Every challenge is a chance to optimize, automate, and occasionally wonder if I'm debugging my code or my life choices.

Full Stack 🖥️

With full stack experience, I obsess over UI quirks nobody notices until I fix them.. push API speeds until the server questions physics, and optimize databases because slow queries are basically passive-aggressive notes from the system. Call it engineering.. I call it therapy with indexes.

Innovation 🔧

My projects involve automation, AI, and integrations.. because if technology won't slow down, someone has to decide whether it's true innovation or just another “what if we made this absurdly complicated” experiment. Spoiler.. it's usually the second one.

Security 🔐

Good security is like good health.. invisible until something goes horribly wrong. That's why I build with layered defenses, AI-driven monitoring, and a healthy dose of paranoia, so the only unexpected surprises are me coding directly to production.

Automation 🤖

I use automation to improve efficiency, reduce errors, and eliminate soul crushing repetition. If I have to do the same manual task more than three times, it's a bug to me.

Integrations 🔗

APIs are like dinner guests—some chat perfectly in REST, others require middleware to stop making a scene, and a few just ghost everyone with a silent 504. I step in to keep the data (and the holiday spirit) going.

Privacy 🕵️‍♂️

I take data privacy so seriously that even my own systems struggle to remember what they just processed. While some see compliance as an inconvenience, I see it as an art, a dance of encryption, access controls, and politely telling bad actors to ‘try hacking someone else.' Rest assured.. your data is locked down tighter than a secret family recipe… unless, of course, you're still using password123

Meet My Work 🏗️

My portfolio is a collection of projects where I've battled performance bottlenecks, tamed security headaches, and trained AI that occasionally insists it's the senior engineer. Each project is a mix of problem-solving, debugging, and existential irony.. also known as software engineering at scale.

I am Charis

I apply SOLID, DRY, and sarcasm daily. I use AI to apply recursion.. mostly to remind me I fine tuned it to be more opinionated than me.

Athens, Greece

Monday - Friday, 18:00 - 22:00
Saturday - Sunday, 10:00 - 22:00

Professional Portfolio

Showcasing enterprise-grade projects that demonstrate senior engineering expertise and real industry value.

Enterprise ERP/CRM System

2025-2026 Enterprise SaaS

Architected, designed, and built a comprehensive enterprise ERP/CRM system from ground up. Responsible for complete technology stack selection, design pattern implementation (Strategy, Factory, Cascade etc.), modular monolith architecture, enterprise security design, logging infrastructure, and full project management of this massive undertaking.

Technology Stack:

PostgreSQL
React
Docker
Azure
ORM
CI/CD
Monitoring
Logging
Testing
Quality Assurance
Deployment
Project Management

Architectural & Technical Leadership:

Full-Stack Architecture: Designed modular monolith with clear domain boundaries and microservice-ready structure
Design Pattern Implementation: Strategy pattern for business rules, Factory pattern for entity creation, Cascade pattern for data relationships
Technology Stack Curation: Selected and configured Python/FastAPI, PostgreSQL, SQLAlchemy, Alembic, React, Docker, Azure infrastructure
Enterprise Security Design: Multi-layered security architecture with authentication, authorization, data encryption, and audit logging
Multi-Tenant Architecture: Designed scalable tenant isolation with role-based access control and department-level permissions
Project Management: End-to-end project leadership including requirements gathering, sprint planning, and delivery coordination
Advanced Features: Real-time synchronization, AI integration, automated workflows, comprehensive reporting, compliance frameworks
Production Infrastructure: Complete DevOps setup with CI/CD pipelines, monitoring, logging, and deployment automation

Data Migration & Integration Pipelines

2023-2024 Data Engineering

Architected and implemented robust data migration pipelines for legacy system modernization, featuring Excel/JSONL import/export, Alembic database migrations, and ISO compliance validation.

Technology Stack:

Python
Pandas
Alembic
PostgreSQL
Apache Airflow
Redis
Docker

Key Features:

Automated data validation and cleansing pipelines
Zero-downtime database schema migrations
Real-time data quality monitoring and alerting
ISO compliance validation and reporting
Rollback mechanisms and data integrity checks

Vessel Tracking & Geospatial APIs

2022-2023 Geospatial Platform

Built high-performance geospatial APIs for real-time vessel tracking, featuring PostGIS integration, GeoJSON processing, historical trend analysis, and predictive route optimization.

Technology Stack:

Python
PostGIS
FastAPI
MapLibre GL JS
Redis
WebSockets
Docker

Key Features:

Real-time vessel position tracking and visualization
Advanced spatial queries and geofencing capabilities
Historical route analysis and pattern recognition
Weather integration and route optimization
High-performance caching for sub-second response times

Greek Web Scraper (pip package)

2024 Published Package

Published pip-installable Python package (pip install greek-web-crawler) for large-scale Greek-language web crawling with GPU-accelerated NLP filtering and intelligent content extraction. Built for scalability, reliability, and automation in data collection workflows.

Technology Stack:

Python (Scrapy Framework)
CUDA (GPU Acceleration)
NLP (spaCy + Custom Models)
Unicode Normalization
Parallel Processing
JSONL Output Format
Smart Retry Logic
Error Handling

Package Features:

High-Speed Crawling: Scrapy-based architecture with concurrent request handling
GPU-Powered Processing: CUDA acceleration for Greek text filtering and classification
AI-Enhanced Cleaning: NLP techniques for noise reduction and content normalization
Smart Error Handling: Automatic encoding detection and bad request avoidance
Structured Output: Clean JSONL format for downstream analysis and ML training
Production Ready: Published on PyPI, comprehensive documentation, unit tests

Custom LLM Fine-Tuning

2024 ML Research

Advanced LLM fine-tuning pipeline implementing LoRA (Low-Rank Adaptation) techniques on multiple model architectures. Specialized for structured data extraction, JSON output generation, and domain-specific tasks with comprehensive evaluation and deployment strategies.

Technology Stack:

Python
Transformers (HuggingFace)
LoRA + QLoRA
PEFT (Parameter Efficient Fine-Tuning)
jsonformer
RAG Pipelines
Weights & Biases
TensorBoard
CUDA + Mixed Precision

Fine-Tuning Features:

Multi-Model Support: TinyLlama (1.1B), Phi-4 Mini (14B), Gemma 3B with architecture-specific optimizations
LoRA Adapters: Parameter-efficient fine-tuning with rank optimization and alpha scaling
Structured Output: JSON schema enforcement, constrained generation, format validation
Custom Training Pipelines: Domain-specific datasets, curriculum learning, progressive fine-tuning
RAG Integration: Retrieval-augmented generation with vector databases and embedding models
Evaluation Framework: BLEU, ROUGE, custom metrics, human evaluation protocols
Production Deployment: Model quantization, ONNX conversion, inference optimization
Experiment Tracking: Comprehensive logging, hyperparameter tuning, model versioning

PDF → Structured Data Extractor

2023 Automation Tool

Intelligent document processing system that converts scanned PDFs into structured data using advanced OCR, template matching, and ML-based field extraction. Seamlessly integrates with ERP systems for automated invoice processing and data validation.

Technology Stack:

Python
pdf2data + PyPDF2
Tesseract OCR
OpenCV (Image Processing)
Jinja2 Templates
JSON Schema Validation
Regular Expressions
Pandas (Data Processing)
FastAPI (REST Endpoints)

Document Processing Features:

Advanced OCR: Multi-language text recognition with confidence scoring and error correction
Template System: Custom extraction templates for invoices, receipts, and business documents
Field Detection: ML-based identification of key fields (amounts, dates, vendor info)
Data Validation: JSON schema validation, business rule enforcement, duplicate detection
ERP Integration: Direct API connections to accounting systems and workflow automation
Batch Processing: High-throughput document processing with parallel execution
Quality Assurance: Confidence scoring, manual review queues, audit trails
Error Handling: Robust exception handling, retry mechanisms, logging and monitoring

AI Email Intelligence Engine

2024 Production AI

Production-grade AI system that intelligently replies to supplier emails based on current warehouse stock. Uses LLM + RAG to find alternative products when exact matches aren't available, automatically generating quotations with optimal pricing strategies.

Technology Stack:

Python
LangChain
Ollama API
Gmail API
ChromaDB
FastAPI
OpenPyXL
Cosine Similarity
Async Programming

Key Features:

Intelligent product matching with embedding-based similarity search
Automated alternative product suggestions when stock unavailable
Dynamic pricing optimization based on market conditions
Structured JSON output for seamless ERP integration
Real-time warehouse inventory synchronization
Multi-language supplier communication support

AI-Powered Firewall

2024 ML + Cybersecurity

Experimental ML-enhanced firewall that dynamically detects and mitigates cyber threats in real-time. Trained on 2M+ Apache2 logs using machine learning models to classify network traffic and adapt to evolving attack patterns.

Technology Stack:

Python
Scikit-learn
Logistic Regression
Apache2 Logs
Network Security
Anomaly Detection
Data Preprocessing
Feature Engineering

Key Features:

AI-driven threat classification with 95%+ accuracy
Dynamic adaptation to new attack patterns
Automated response mechanisms with failsafe mode
Custom synthetic attack scenario generation
Real-time log analysis and threat scoring
Integration-ready for automated IP blocking systems

Advanced JWT Security Layer

2023-2024 Enterprise Security

Enterprise-grade security layer implementing the most comprehensive authentication and authorization system for web applications. Features advanced JWT management, multi-factor authentication, RBAC with granular permissions, CSRF protection, dual login mechanisms, and sophisticated threat detection.

Technology Stack:

Python
JWT (RS256/ES256)
Redis Cluster
Lua Scripts
Device Fingerprinting
RBAC + ABAC
CSRF Tokens
TOTP/HOTP
bcrypt + Argon2
Rate Limiting

Enterprise Security Features:

Advanced JWT Management: RS256/ES256 signing, automatic key rotation, token blacklisting
Multi-Factor Authentication: TOTP, SMS, email verification, hardware tokens
Role-Based + Attribute-Based Access Control: Granular permissions, department isolation, resource-level security
Session Management: Redis-backed sessions, concurrent login limits, device tracking
CSRF Protection: Double-submit cookies, SameSite attributes, origin validation
Dual Login Systems: Admin/user portals with separate security policies
Threat Detection: Brute force protection, anomaly detection, IP reputation scoring
Audit & Compliance: Comprehensive logging, GDPR compliance, SOC2 ready

Dockerized DevOps Stacks & CI/CD

2022-2025 Infrastructure

Architected comprehensive DevOps infrastructure with multi-container orchestration, custom CI/CD pipelines, and cost-optimized Azure agents. Features automated testing, deployment strategies, full rollback capabilities, and infrastructure as code for maximum reliability and cost management.

Technology Stack:

Docker Compose
Azure DevOps
Custom Azure Agents
Terraform
Ansible
Nginx + Certbot
PostgreSQL + PostGIS
Redis Cluster
Prometheus + Grafana
ELK Stack

DevOps & CI/CD Features:

Multi-Container Orchestration: FastAPI, PostgreSQL/PostGIS, Redis, Nginx, monitoring stack
Custom CI/CD Pipelines: Multi-stage builds, parallel testing, automated deployments
Azure Custom Agents: Cost-optimized self-hosted agents with auto-scaling and resource management
Comprehensive Testing: Unit tests, integration tests, security scans, performance benchmarks
Deployment Strategies: Blue-green deployments, canary releases, feature flags
Full Rollback System: Database migrations, container versioning, configuration snapshots
Infrastructure as Code: Terraform for provisioning, Ansible for configuration management
Monitoring & Alerting: Real-time metrics, log aggregation, automated incident response

Network Segmentation (UDM Pro)

2025 Network Security

Designed and implemented a fully segmented enterprise-grade network hosting multiple device categories with strict isolation. Features dedicated VLANs for IoT devices, administrative systems, servers, and guest access with comprehensive security policies and inter-VLAN routing controls.

Technology Stack:

UniFi Dream Machine Pro
802.1Q VLAN Tagging
Layer 3 ACLs
Stateful Firewall
IDS/IPS
DPI (Deep Packet Inspection)
Network Access Control
RADIUS Authentication

Network Security Architecture:

IoT VLAN (10.0.10.0/24): Isolated smart devices, no internet access, local communication only
Admin VLAN (10.0.20.0/24): Management systems, servers, privileged access with MFA
Server VLAN (10.0.30.0/24): Production servers, database systems, API endpoints
Guest VLAN (10.0.40.0/24): Isolated internet access, no internal network visibility
DMZ VLAN (10.0.50.0/24): Public-facing services with strict ingress/egress controls
Advanced Security: IDS/IPS monitoring, DPI traffic analysis, geo-blocking
Access Controls: Time-based policies, device fingerprinting, MAC address filtering
Monitoring & Logging: Real-time traffic analysis, security event correlation, automated alerting

Enterprise Network Design (Cisco)

2023-2024 Academic Project

Designed and simulated a fully functional enterprise-grade network using Cisco Packet Tracer, implementing comprehensive VLANs, routing protocols, security policies, and high availability mechanisms for a scalable corporate environment with departmental segmentation.

Technology Stack:

Cisco Packet Tracer
Hierarchical Network Design
VLANs + VTP
HSRP (High Availability)
ACLs (Access Control Lists)
DHCP + Static Routing
NAT/PAT
Port Security + BPDU Guard
Inter-VLAN Routing

Network Architecture Features:

Hierarchical Design: Core, Distribution, and Access layers for optimized scalability and management
Departmental VLANs: Logical separation for IT, Finance, HR, Sales with dedicated subnets
VTP Management: Centralized VLAN configuration for simplified network administration
High Availability: HSRP failover ensuring continuous network uptime and redundancy
Security Implementation: Custom ACLs, Port Security, BPDU Guard, disabled unused ports
Routing & Connectivity: Static routing, Inter-VLAN routing, DHCP automation
Internet Access: NAT/PAT for controlled external communication and address translation
Network Management: Centralized switching, structured cabling, scalable architecture

Image Recognition System

2024 Deep Learning

Advanced deep learning image recognition system implementing state-of-the-art CNN architectures for multi-class object detection and classification. Features custom model architectures, data augmentation pipelines, and optimized inference for real-time processing with high accuracy across diverse datasets.

Technology Stack:

Python
TensorFlow 2.x
Keras
OpenCV
NumPy + Pandas
ResNet/EfficientNet
YOLO/SSD
Data Augmentation
Transfer Learning
TensorRT

Deep Learning Features:

Custom CNN Architectures: ResNet-50/101, EfficientNet variants, custom attention mechanisms
Multi-Task Learning: Object detection, classification, and semantic segmentation
Advanced Data Pipeline: Automated augmentation, normalization, batch processing
Transfer Learning: Pre-trained models fine-tuned on domain-specific datasets
Real-Time Inference: TensorRT optimization, model quantization, edge deployment
Performance Optimization: GPU acceleration, mixed precision training, distributed processing
Model Evaluation: Comprehensive metrics, confusion matrices, ROC analysis
Production Ready: REST API endpoints, batch processing, monitoring and logging

Charalampos Nikolaidis - Software Engineer - Athens, Greece

Career 💡

Full Stack 🖥️

Innovation 🔧

Security 🔐

Automation 🤖

Integrations 🔗

Privacy 🕵️‍♂️

Meet My Work 🏗️

I am Charis

Professional Portfolio

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Technical Glossary