Secure systems engineer

Senior Backend Software Engineer

John Roest

I design and build business-critical backend systems with Java, Kotlin and Spring Boot. My work sits where architecture, reliability and clear communication meet: turning complex business needs into secure software that teams can operate with confidence.

runtime.profileONLINE

Backend ArchitectureJava / Kotlin / Spring BootDistributed SystemsSecurity-first delivery

9+Years engineering

24/7Production mindset

Core philosophy

Most software projects fail because of unclear conversations, shifting expectations, and fragmented ownership. Business and IT are not separate worlds. They are partners in the same process.

Experience timeline

Security-minded delivery for regulated environments.

2025 - Present

Project Lead and Senior Backend Engineer

Netherlands Forensic Institute

Leading a four-person engineering team while staying hands-on in Java and Spring Boot for business-critical forensic systems.

Architecture and implementation for Dutch DNA Database services
PRÜM exchange API work with secure cross-border integration concerns
Contract testing to reduce integration risk between teams and systems
Kubernetes, OpenShift and Docker improvements for reliable delivery

2021 - Present

Fullstack Software Engineer

Sopra Steria

Building secure backend systems, mentoring engineers, and translating complex business needs into maintainable software.

Java, Kotlin and Spring Boot backend architecture
Technical decision-making in regulated environments
Engineering quality through reviews, automated tests and CI/CD

2021 - 2025

Backend and Mobile Developer

Coöperatie VGZ

Delivered mobile and backend capabilities in healthcare, with a strong focus on search, delivery pipelines and system quality.

React Native architecture and Java Spring Boot APIs
Elasticsearch search strategy and stakeholder alignment
Trunk-based development and release automation

2016 - 2021

Software Developer

MoneyMonk

Grew from mobile development into backend architecture, including secure financial integrations and greenfield Kotlin services.

Legacy PHP API migration to Java and Kotlin
PSD2 banking integrations and KYC platform development
iOS, Android and backend ownership across product delivery

Technical stack

Tools chosen for maintainable, high-confidence systems.

Languages

JavaKotlinSwiftTypeScript

Frameworks

Spring BootReact NativeNext.jsNode.js

DevOps

KubernetesOpenShiftDockerCI/CD

Architecture

REST APIsContract TestingPostgreSQLSecurity

Writing

Notes on architecture, engineering culture and delivery.

August 26, 2026 · 4 min readGood Leadership in ITThere is a simple test for leadership.

EngineeringLeadership

May 11, 2026 · 9 min readWhat building Orevox taught meTwo months of building, failing, and figuring things out as a developer and founder

EngineeringDevOpsJavaArchitectureAI

March 11, 2026 · 5 min readHow Large Pull Requests Are Killing Your Delivery SpeedIn many software teams, the pattern is all too familiar: a developer works for days on a feature branch, opens a pull request with hundreds of lines changed, and waits for someone to find time to review it. The PR sits i

EngineeringDevOps

January 24, 2026 · 6 min readDrone detection with code!Object detection is one of the most compelling applications of computer vision. Unlike image classification—which tells you what is in an image—object detection also determines where those objects are located. This enabl

November 24, 2025 · 3 min readBuilding a Drone Detection System with YOLO and PythonI am building an application that uses computer vision to identify drones in video streams. The setup is straightforward: a camera sends frames to a server, the server analyzes them in real time, and if a drone enters th

November 10, 2025 · 4 min readWhen Business Meets ITEvery few months, it happens again.

September 15, 2025 · 4 min readEvent Driven SystemsArchitects love drawing event-driven diagrams. A clean box labeled "Order Service" sends an arrow to a queue, then boxes labeled "Inventory," "Payments," and "Notifications" light up. Everything looks decoupled, flexible

September 8, 2025 · 3 min readPackage StructureWhen you generate a new Spring Boot project, the framework establishes a default package structure. It looks basic. Many developers, particularly those who prefer organizing things their own way, are tempted to move file

Spring BootArchitecture

August 12, 2025 · 3 min readImmutability in javaAn immutable object's state cannot change after it is created. That constraint sounds simple, but its consequences are significant—particularly in multi-threaded systems.

July 17, 2025 · 4 min readThe Code That Knew What It WantedI did not always write tests first. I thought it was a waste of time. Why write tests for code that does not exist yet? Write the implementation, then verify it works.

June 26, 2025 · 3 min readWhy Zod Is a Game Changer for Runtime Validation in TypeScriptTypeScript catches type errors at compile time. That coverage ends at the application boundary. When data arrives from an API, a form, or a configuration file, TypeScript has no mechanism to verify it matches the declare

June 4, 2025 · 3 min readThe Builder Design PatternThe Builder pattern is a creational design pattern for constructing complex objects step by step. It provides a clear, flexible approach when an object has many optional fields or configurations.

Design PatternsJava

April 1, 2025 · 4 min readThe Factory Method: Encapsulating Object CreationObject creation starts simple: call new, pass some parameters, get an object. As the codebase grows and requirements shift, that simplicity erodes.

Design Patterns

February 3, 2025 · 3 min readUnderstanding the Singleton Pattern in KotlinThe Singleton pattern ensures that a class has exactly one instance throughout the application's lifetime and provides a global point of access to it. It is one of the most commonly reached-for patterns and one of the mo

Design PatternsKotlin

January 15, 2025 · 4 min readThe C4 Architecture ModelArchitecture diagrams fail in a predictable way. Someone draws boxes and arrows on a whiteboard, labels them with component names, and calls it documentation. Three weeks later, a new team member opens the diagram and ca

October 17, 2024 · 3 min readCQRS with Spring Boot and Java: The Why Behind the PatternCQRS—Command Query Responsibility Segregation—separates the way you handle reading data from the way you handle writing data. Rather than using a single model for both operations, CQRS splits them into two distinct model

ArchitectureSpring Boot

August 27, 2024 · 4 min readDeveloping a Simple Game in Plain Java with Swing: My Journey So FarI recently started building a small game in plain Java with Swing—no game engine, no external framework. The goal was to understand the mechanics of a game loop from the ground up. So far, the result is a player sprite t

August 19, 2024 · 2 min readThe Case for Small Pull Requests: Lessons Learned from a Big MistakeThe advice is everywhere: keep pull requests small and focused. Most developers have heard it. Many still submit large ones anyway—usually with good intentions.

July 25, 2024 · 3 min readAPI IdempotencySpring Boot and Kotlin make a well-matched pair for building REST APIs. Spring Boot eliminates the boilerplate associated with traditional Spring configuration, while Kotlin's null safety, concise syntax, and idiomatic d

Spring BootKotlin

July 12, 2024 · 3 min readUnderstanding OWASP and AuthenticationSecurity is not an optional feature to add at the end of a project. Vulnerabilities in authentication are consistently among the most exploited weaknesses in web applications. Understanding the established baseline—and a

May 1, 2024 · 3 min readNavigating the Murky Waters of JavaScript Exceptions: A TypeScript PerspectiveJavaScript's runtime error model is one of its most persistent pain points. There is no throws declaration, no checked exceptions, and no compile-time contract that tells you which functions can fail and under what condi

JavaScriptTypeScript

April 10, 2024 · 3 min readDemystifying Docker and Containerization: A Beginners GuideDocker is an open-source platform for packaging and running applications in isolated environments called containers. A container bundles the application and all its dependencies—libraries, configuration, runtime—into a s

April 2, 2024 · 3 min readExploring the Power of TypeScriptJavaScript is dynamically typed. Variables have no declared type, function parameters carry no contract, and a function that expects a string will silently accept a number at runtime. This flexibility is useful in small