Senior / Lead Software Engineer with 15+ years of experience building backend, full-stack, cloud, and distributed systems.

My recent work spans Java/Spring Boot platforms, cloud-native Python services, React/Vue applications, security and authorization systems, and production infrastructure across AWS, GCP, and Azure.

I tend to work on systems where the difficult part isn't just writing the feature — it's understanding how the application behaves under load, across service boundaries, and when something fails in production.

• 🔭 Working on: Distributed backend systems, cloud platforms, security/authorization, and full-stack applications
• 💬 Ask me about: Java/Spring Boot, Python/FastAPI, system design, production debugging, APIs, AWS/GCP, SSO/OAuth/SAML
• ⚡ Particularly interested in: Reliability, security, event-driven systems, applied AI, and difficult production problems

• Backend & API Engineering — Java/Spring Boot, Python/FastAPI, Node.js
• Distributed & Event-Driven Systems
• Production Debugging — logs, tracing, concurrency, networking, IAM
• Authorization & Identity — Apache Ranger, SSO, SAML, OAuth, FIDO2
• Cloud Architecture — AWS, GCP, Azure
• Full-Stack Development — React, Vue.js, Angular, Next.js
• Data & Performance — PostgreSQL, MySQL/Aurora, MSSQL, Redis
• Containers & Infrastructure — Docker, Kubernetes, Terraform, CI/CD
• Applied AI — LLM integrations, agent workflows, Vertex AI, RAG

• Work on Java-based authorization and security functionality in Apache Ranger
• Develop and test resource-level authorization behavior and security-related backend changes
• Debug complex behavior across distributed data-platform components
• Contribute changes through upstream/open-source and enterprise release workflows

• Develop a Spring Boot and Vue.js application supporting large pharmacy-audit workflows
• Diagnose concurrency, queueing, timeout, and batch-processing failures in production-style workloads
• Work with AWS services, Aurora/MySQL, SSM, CloudWatch, Liquibase, and containerized/cloud infrastructure
• Improve reliability of long-running asynchronous jobs and service integrations

• Helped design and implement an AI-powered application using Python, FastAPI, Angular, GCP, and Vertex AI
• Built backend APIs and asynchronous application workflows
• Worked with Redis, Pub/Sub, Firebase, IAM, containers, CI/CD, and cloud deployments
• Integrated LLM-driven workflows while keeping deterministic application behavior around the AI layer

• Helped migrate an existing Unity-based simulation interface to a modern React web application
• Built workflows for scenario creation, simulation jobs, filtering, tagging, and map-based interaction
• Worked with React, TypeScript, Mapbox, Docker, nginx, Kubernetes, and Azure infrastructure

• Led development and modernization of backend and full-stack applications
• Worked across Python, FastAPI, React/Next.js, relational databases, AWS, Docker, and Terraform
• Diagnosed production performance and reliability issues across application and infrastructure layers
• Supported architecture, technical direction, CI/CD, and production operations

• Developed enterprise security and access-control systems
• Modernized legacy applications toward service-oriented and cloud architectures
• Worked with event-driven processing using Kafka and RabbitMQ
• Built and supported identity integrations including SSO, SAML, and OAuth

Languages: Java, Python, TypeScript, JavaScript, C#, SQL
Backend: Spring Boot, FastAPI, Django, Node.js, .NET Web API
Frontend: React, Next.js, Vue.js, Angular
Cloud: AWS, GCP, Azure
Data: PostgreSQL, MySQL / Aurora, MSSQL, Redis, Firestore, DynamoDB
Messaging: Kafka, RabbitMQ, Google Pub/Sub, SQS
Infrastructure: Docker, Kubernetes, Terraform, GitHub Actions, CI/CD
Security: Apache Ranger, IAM, SSO, SAML, OAuth
Observability: CloudWatch, OpenTelemetry, Prometheus, Grafana, ELK / Kibana

• GitHub: https://github.com/oldmcdonnell
• LinkedIn: https://www.linkedin.com/in/mcdonnell-eoin

"Build systems that work. Fix systems that don't. Understand why."