THE ENGINEER BEHIND THE BLOG

Jeffrey Sylvan

Staff / Principal Software Engineer · Distributed Systems, Platform, and AI Infrastructure.
Arlington, MA (Boston area) · remote-friendly.

Email Jeff LinkedIn Resume · PDF GitHub

Selected impact

100s of engineers adopted the delivery pipeline he built First Republic Bank · deploys moved from days to minutes · resume
90% lower server and development cost per game Apocoplay · founder and CTO · team of 20 · resume
1st backend-led production ML application, with full MLOps CarGurus · highlighted on an investor earnings call · resume
10,000 player battle architecture, designed and published in public Black Skies · thesis · benchmark ledger
The short version

I'm Jeff Sylvan, a Staff/Principal software engineer focused on distributed systems, platform engineering, and AI infrastructure.

Before this break I was a Principal Engineer at CarGurus. Earlier work includes production ML infrastructure, delivery systems used by hundreds of engineers, commerce-platform rebuilds at global scale, and real-time multiplayer engines at two game studios, one of them mine.

I stepped away in February 2026 to care for my family. During the break I built Black Skies in public as a work sample: eight posts, 25 hand-built diagrams, benchmark plans, test evidence, and the implementation record for a 10,000-player real-time battle system. Custom automation and LLM tooling sit behind the workflow. The goal is simple: show how I reason about Staff-level systems work when there is no interview prompt and no scaffolding. The receipts start at the build ledger.

Impact case notes
CARGURUS · 2023-2026

First ML app out of backend engineering

Led the first non-data-science team to ship a production ML application with a full MLOps pipeline. Highlighted to investors on an earnings call, and the path it opened is now walked by other backend teams.

FIRST REPUBLIC BANK · 2018-2023

Deployments: days to minutes

Built the continuous delivery pipeline that took releases from days to minutes, drove adoption across hundreds of engineers, and trained 50+ engineers, architects, and directors on the practices behind it.

CIMPRESS (VISTAPRINT) · 2015-2017

The rebuild that unblocked the EU

Found the scaling flaw in core commerce infrastructure that compounded with every acquisition and threatened EU sales. Won cross-department buy-in, led the rebuild, and handed a junior team a platform that ran incident-free at thousands of queries per second.

APOCOPLAY · 2012-2015

90% lower cost per game

Founded the studio, led a team of 20, and built a server-side engine for large-scale multiplayer games that cut server and development costs by 90%, saving hundreds of thousands of dollars per title annually.

COGNICLUSTER · 2026

The work sample you are reading

Designed and published the Black Skies architecture solo: eight posts, 25 hand-authored diagrams, 1,000+ test methods and chaos suites passing in the repo, and every unproven claim tagged with the load test that would falsify it.

What the break produced

Everything below was designed, written, built, and operated between February 2026 and now, by one person and the automation he built.

THE ARCHITECTURE · 8 POSTS

Black Skies

A 10,000-player battle design with no time dilation, argued in public with diagrams, benchmark plans, and published falsifiers.

Start with the thesis →
THE ORCHESTRATION LAYER · RELATED PROJECT

Ambient Agents

A reconciliation kernel for the agent workflow that helps build Black Skies. Designed in public with a published kill condition.

The project →
THE DISCIPLINE

The ledger

What has been measured, what has not, and exactly what would falsify the design. The honesty budget the whole series runs on.

Read the ledger →
THE COMPANY

CogniCluster LLC

The one-person shop behind all of it: sites, infrastructure as code, CI, and the automation, built and operated solo.

cognicluster.com →
Career record
2026 - now
Public work sample during family-care break · Staff/Principal-level systems work, in publicBlack Skies architecture, benchmarks, diagrams, tests, and this blog, built through CogniCluster LLC (a one-person shop).
2023 - 2026
CarGurus · Principal Software EngineerProduction ML out of backend engineering, ADRs and architecture reviews, monolith to services.
2018 - 2023
First Republic Bank · Senior Software Engineer, Principal scopeContinuous delivery adopted by hundreds of engineers; training for 50+.
2017 - 2018
HubSpot · Senior Software EngineerKafka-backed identity and user-data pipelines.
2015 - 2017
Cimpress (Vistaprint) · Lead Software EngineerThe tax-infrastructure rebuild that unblocked EU sales.
2012 - 2015
Apocoplay · Founder and CTO20-person studio; 90% cost reduction per game ported to its engine.
2001 - 2012
Earlier · Allscripts · Council for Logistics Research · PRTM · QScendHospital finance, defense logistics for the Office of the Secretary of Defense, municipal software.

University of Hartford, B.S. Computer Science · MIT certificates in Data Science and Blockchain · MIT Start Smart and Invest Smart.

If you are evaluating me for a role: the resume is two pages, this blog is the work sample, and the fastest honest tour is the thesis followed by the ledger. Email me and I will respond quickly.