David Xie Li
I build and measure the systems behind real-time communication.
Software Engineer II at Microsoft, working across the Teams calling stack — from protocol-level encryption to the telemetry pipelines and dashboards that prove a release is actually healthy.
Core technologies
- C++
- TypeScript
- Kusto / KQL
- Power BI
- Azure
- AWS
- React
- Python
- Cryptography
- Observability
- Real-time media
- Kubernetes
- Docker
- C#
- SQL
- Node.js
- Wireshark
- MISP
100K
attendee scale
Meeting features and message-path optimizations built for 100,000-user Teams events.
#1
GPA in degree & faculty
Highest grade point average in Computer Science and across the Faculty of Engineering, UCR.
8
Microsoft certifications
Azure administration, networking, AI engineering, security and Microsoft 365.
4
international competitions
ICPC 2023, two OAS Cyber Challenge CTFs and the OAS CyberVenture Quest hackathon.
About
A feature isn't finished when it merges. It's finished when a signal proves it works.
I'm a software engineer at Microsoft, based in San José, Costa Rica. I work on the client calling stack that powers Microsoft Teams — the code path that runs when hundreds of thousands of people join a call and expect it to just work.
Most of my work lives at two ends of the same problem. On one end: shipping calling features in large cross-platform C++ and TypeScript codebases — restartable Town Hall events, XL meeting support, message-path optimizations for 100,000-attendee meetings. On the other end: building the Kusto telemetry pipelines and Power BI dashboards that tell us whether any of it is actually working in production, and owning the investigations when reliability, latency or telemetry numbers don't agree with each other.
That second half is the part I care most about. A feature isn't finished when it merges; it's finished when there's a signal that proves it behaves correctly for real users, and someone can act on that signal at 3am. I also contribute to security-focused engineering on encrypted communications, including cryptographic key management improvements and rollout validation.
I came into engineering sideways — through cybersecurity. Before Microsoft I helped build CSIRTAmericas at the Organization of American States, a hemispheric network of national incident response teams spanning the Americas, and competed in Capture The Flag events against teams from nine Latin American countries. That background is why I instinctively ask what breaks, who notices, and how we'd know.
I graduated from the University of Costa Rica with the highest GPA in both the Computer Science degree programme and the Faculty of Engineering, taught introductory programming, web, database and C/C++/Python courses as a teaching assistant, and competed at ICPC. I work in Spanish, English, Cantonese and Mandarin.
What I work on
- Real-time systemsTeams client calling stack, cross-platform C++ and TypeScript.
- Telemetry & observabilityKusto pipelines, Power BI, metric definitions, investigations.
- Security engineeringEncrypted communications and cryptographic key management.
Languages
- SpanishNative
- EnglishAdvanced
- CantoneseIntermediate
- MandarinIntermediate
How I work
- Growth mindset
- Problem solving
- Quick learner
- Teamwork
- Leadership
- Customer obsession
- Time management
San José, Costa Rica · UTC−6
Experience
From regional cyber defence to the calling stack used by the world
Five years of moving steadily toward higher-stakes systems — and taking the security instinct along.
Software Engineer II · Microsoft
Mar 2026 — Present
Promoted7 moSan José, Costa RicaTelemetry, analytics and security engineering for real-time and AI-powered calling.
- Contribute to security-focused engineering initiatives, investigating and implementing protocol-level improvements for encrypted communications — including cryptographic key management enhancements and rollout validation planning.
- Lead the design and implementation of telemetry, analytics and reporting solutions for real-time communication and AI-powered calling scenarios, enabling engineering teams to measure reliability, latency and service health.
- Design and deliver Kusto-based telemetry pipelines and Power BI dashboards that turn complex client and service telemetry into engineering insight used for operational decision-making.
- Own end-to-end investigations into reliability, latency and telemetry discrepancies, identifying root causes across multiple telemetry sources and driving fixes that improve data accuracy and diagnostic quality.
- Drive operational excellence through data-driven monitoring, production investigations, deployment validation, alerting analysis and continuous improvement of engineering health metrics.
- Kusto (KQL)
- Power BI
- C++
- TypeScript
- Azure
- Cryptography
- Observability
Software Engineer · Microsoft
Oct 2024 — Mar 2026
Full-time1 yr 6 moSan José, Costa RicaFeature development on the Microsoft Teams client calling stack and Microsoft 365 self-help experiences.
- Worked on the client calling stack supporting Microsoft Teams infrastructure and calling features, delivering enhancements that improved product usability and user experience.
- Designed and implemented multiple features including the ability to restart Town Hall events, XL meeting functionality, and message optimizations for 100,000-user meetings.
- Implemented application components using test-driven development while adhering to agile methodologies.
- Refactored, maintained and improved large cross-platform codebases in both C++ and TypeScript.
- Developed customer self-help and online support experiences for Microsoft 365 worldwide commercial and consumer users — delivering personalised insights and answers that reduced Incidents per Million Engaged Users (IMEU) while increasing self-help success rates and customer satisfaction.
- Collaborated with cross-functional teams to design and develop features that address customer needs and improve the overall support experience.
- C++
- TypeScript
- React
- TDD
- Agile
- Cross-platform
- Microsoft 365
Software Development Engineer · Amazon
Jan 2024 — Sep 2024
Full-time9 moSan José, Costa RicaServerless tooling and APIs for Amazon's worldwide hardware asset management.
- Built products (internal tools and web applications) and services (backend processes and APIs) supporting the Asset Management tooling that tracks and audits Amazon's worldwide hardware asset ordering — laptops, monitors and peripherals.
- Leveraged AWS to build and deploy scalable, reliable serverless solutions operating at global scale, delivering low-latency, highly available services for a diverse range of stakeholders.
- Participated in code reviews and provided constructive feedback to raise overall codebase quality.
- Used agile development methodologies to ensure timely delivery of high-quality software.
- AWS
- Serverless
- APIs
- TypeScript
- Java
- Agile
Technical Support Engineer Intern · Microsoft
Feb 2023 — Aug 2023
Internship7 moSan José, Costa RicaExchange Online diagnostics, log analysis and source-level product feedback.
- Communicated directly with customers to understand and promptly resolve Exchange Online (EXO) issues.
- Used log analysis and troubleshooting tools to break down complex problems and develop tailored solutions.
- Collaborated with senior engineers to analyse EXO source code and provide feedback for product enhancement.
- Participated in case triage meetings, contributing insights on challenging problems and promoting cross-functional cooperation.
- Exchange Online
- PowerShell
- Log analysis
- Microsoft 365
- Debugging
Cybersecurity Consultant Intern · Organization of American States (OAS)
Nov 2020 — Sep 2021
Internship11 moSan José, Costa RicaBuilt CSIRTAmericas, a hemispheric network of national incident response teams.
- Increased cybersecurity capability across OAS Member States by developing CSIRTAmericas — a hemispheric network of National Computer Security Incident Response Teams that exchanges threat information, provides technical assistance, trains specialists and strengthens regional incident response.
- Designed instruments to evaluate the use of CSIRTAmericas services among Member State CSIRTs and ran a study to identify service improvements.
- Helped organise capacity-building initiatives including workshops, cybersecurity exercises and regional events.
- Performed functional testing in the MISP (Malware Information Sharing Platform) CSIRTAmericas laboratory and created supporting materials to streamline MISP adoption for Member State CSIRTs.
- MISP
- Threat intelligence
- Incident response
- Security research
Selected work
Systems I've shipped, and how I knew they worked
Case studies from Microsoft, Amazon and the Organization of American States. Scoped to what's publicly describable — architecture and reasoning, not proprietary detail.
Telemetry & analytics for real-time and AI-powered calling
Turning raw client and service signals into the numbers engineers actually act on.
- Kusto (KQL)
- Power BI
- Azure
- C++
- TypeScript
- Distributed tracing
- Data modelling
KQL → BI
signal to decision
Protocol-level improvements for encrypted communications
Cryptographic key management enhancements, shipped with a validation plan attached.
- Cryptography
- Key management
- Protocol design
- C++
Restartable Town Halls and XL meeting support
Features on the Teams client calling stack, built for events where failure is very public.
- C++
- TypeScript
- Cross-platform
- TDD
Message-path optimization for 100,000-attendee meetings
Making the messaging path behave when the attendee count has five zeros.
- C++
- TypeScript
- Performance profiling
- Scalability
Worldwide hardware asset management platform
Serverless tooling to track and audit Amazon's global hardware ordering.
- AWS
- Serverless
- REST APIs
- TypeScript
CSIRTAmericas — a hemispheric incident response network
Helping 30+ nations share threat intelligence and respond to incidents together.
- MISP
- Threat intelligence
- Incident response
- Security research
Microsoft 365 self-help and online support experiences
Answering the customer's question before it becomes a support ticket.
- TypeScript
- React
- Microsoft 365
- Personalisation
Technical profile
Depth where it counts, breadth where it helps
Highlighted items are the tools I use in production work — the rest is real, working familiarity.
Languages
Daily drivers are C++ and TypeScript in large cross-platform codebases; KQL for everything measurement-related.
- C++
- TypeScript
- Python
- C#
- C
- Java
- JavaScript
- SQL
- R
- HTML5
- CSS3
Real-time & client systems
Feature work on the Teams calling stack — high blast radius, cross-platform, and unforgiving about latency.
- Client calling stack
- Cross-platform C++/TS
- Large-scale meetings
- Performance profiling
- Test-driven development
- Legacy refactoring
- Agile delivery
Telemetry, data & observability
The half of the job that proves the other half worked: pipelines, metric definitions, dashboards, investigations.
- Kusto / KQL
- Power BI
- Telemetry pipelines
- Reliability & latency metrics
- Alerting analysis
- Root-cause investigation
- Microsoft SQL Server
- MongoDB
- Tableau
Cloud & platform
Certified across Azure administration, networking and AI engineering; shipped global serverless systems on AWS.
- Azure
- AWS serverless
- Docker
- Kubernetes
- PowerShell
- Linux
- Windows
- Exchange Online
- Microsoft 365
Security engineering
Started in cybersecurity at the OAS and never left it behind — now applied to encrypted communications at Microsoft.
- Encrypted communications
- Cryptographic key management
- Threat intelligence (MISP)
- Incident response
- Wireshark
- Nessus
- OWASP ZAP
- Capture The Flag
Product & web engineering
Front-of-the-stack work for Microsoft 365 self-help experiences and internal tooling.
- React
- Node.js
- .NET
- React Native
- Tailwind CSS
- Bootstrap
- Cypress
- Selenium
- Git
- Jira
- Android Studio
- LaTeX
Credentials
Eight Microsoft certifications and a first-in-faculty degree
Certifications across Azure administration, networking, AI engineering, security and Microsoft 365.
Exchange Online Support Engineer Specialty
Microsoft · Specialty
May 2023 → May 2025 · renewable
Education
B.Sc. Computer Science & Software Engineering
University of Costa Rica (UCR)
San José, Costa Rica
- Graduated with high honours.
- Highest grade point average in the Computer Science degree programme and across the Faculty of Engineering.
- Teaching assistant for introduction to programming, web development, databases, C, C++ and Python.
Continuing education
High Performance Computing School
Jan 2023National High Technology Center, Costa Rica
Parallel computing, shared-memory and distributed-memory programming, scientific visualisation.
Big Data School
Dec 2022National High Technology Center, Costa Rica
Data processing and analysis tooling, computational thinking, machine learning with Python.
Creating a Career Path in Cybersecurity
Aug 2020OAS / CICTE — MICITT Costa Rica
Intensive cybersecurity training and professional development programme.
Achievements & leadership
Competing, teaching, and representing Costa Rica
Academic recognition, international competitions, and the community work that came with them.
- 2023
Highest GPA — Computer Science & Faculty of Engineering
University of Costa Rica
San José, Costa Rica
Recognised for academic excellence with the highest grade point average in the Bachelor's degree in Computer Science and across the entire Faculty of Engineering. Graduated with high honours.
Recognition - 2023
International Collegiate Programming Contest (ICPC)
ICPC Foundation
Competed in the world's most prestigious team-based algorithmic programming contest, solving problems under time pressure in C++ and Python.
Competition - 2023
OAS Cyber Challenge 2023 — Capture The Flag
OAS · University of Chile · CSIRT Gob
Santiago de Chile
Competed against participants from nine Latin American countries in a regional Capture The Flag competition hosted in Santiago de Chile.
Competition - 2023
CyberVenture Quest Hackathon
OAS · Tec de Monterrey
Team-based cybersecurity hackathon promoting entrepreneurship and innovation in security products.
Competition - 2022
OAS Cyber Challenge 2022 — Capture The Flag
OAS · Trend Micro · Tec de Monterrey
Mexico City
Competed against participants from eight Latin American countries in a regional Capture The Flag competition hosted in Mexico City.
Competition - 2023
CSS Leadership Video
Microsoft
Selected to represent Costa Rica in a video interview with senior Microsoft leaders, sharing a success story and setting an example for others in the organisation.
Leadership - 2021 — 2023
Teaching Assistant — Programming, Web, Databases, C/C++/Python
University of Costa Rica
Assisted instructors across introduction to programming, web development, database, C, C++ and Python courses, and mentored students through the material to help them succeed.
Leadership - 2022
Women in Engineering — Python workshop
University of Costa Rica
Helped organise and run a Python workshop for high-school girls, sharing engineering career paths and answering questions about navigating university, with the goal of encouraging them to pursue STEM.
Community
Contact
Let's talk about real-time systems, telemetry, or security
Open to conversations about real-time systems, observability and security engineering.
Based in San José, Costa Rica (UTC−6). I read everything that comes through, and reply to anything specific.