Kristof Ringleff
Hands-on engineering for systems that connect, scale and keep running.
For more than 15 years I have built, integrated and run production software. I work full-stack, specialising in Node.js, TypeScript and AWS serverless, with a particular strength in reliable systems connecting e-commerce, payment and accounting platforms.
I founded and built Fooman, whose products have served more than 11,000 paying customers in 160+ countries. I rebuilt its Xero integration as a Node.js platform on AWS serverless in eight weeks, cutting infrastructure cost by around 89%. It now syncs more than $250 million in transactions a year.
Core Competencies
Languages & Frameworks
AWS & Serverless
APIs & Integration
Engineering Practices
AI-Assisted Development
Domains
What I Bring
Production code, end to end
I write the code, test it, deploy it and support it in production. I handled support myself for years, so I know how code behaves once real merchants depend on it. I design for that from the start.
Engineering standards
I bring the habits that keep code working for years: CI/CD pipelines, automated testing, Docker-based development environments and upgrade-safe design. I review code and mentor other developers. These practices kept 18+ products running across more than ten years of platform change.
Integration and modernisation
Most systems do not need a full rebuild. I work out what to keep, what to replace and how to migrate safely without breaking what is already running. I design integrations that move data between systems without silent failures, including OAuth 2.0 and token management.
Influence beyond my own team
I founded and led ExtDN, the Magento Extension Developers Network. I aligned up to 20 independent extension companies on shared quality standards. I represented their collective technical position to Magento and Adobe.
AI-assisted engineering
I build with AI coding agents working from GitHub issues, using test-driven development. The focus is on practical implementation with clear outcomes and using tokens efficiently.
Case Studies
Serverless SaaS Re-Architecture & Compliance Migration
I rebuilt our Xero integration as a Node.js platform on AWS serverless in eight weeks. Xero's mandatory move to OAuth 2.0 meant the existing decentralised extension model was no longer viable. There was a hard external deadline and zero tolerance for service interruption.
Serverless SaaS Re-Architecture & Compliance Migration
I rebuilt our Xero integration as a Node.js platform on AWS serverless in eight weeks. Xero's mandatory move to OAuth 2.0 meant the existing decentralised extension model was no longer viable. There was a hard external deadline and zero tolerance for service interruption.
I chose serverless over containers because demand was spiky. The platform scales with load and charges only for use, replacing a flat monthly cost per server. That decision is where the cost reduction came from.
Outcomes
- Delivered in eight weeks to a fixed external deadline, with no service interruption
- Around 89% lower monthly infrastructure cost
- Horizontal scalability with no capacity planning required
- Achieved Xero Verified App status
- Secure token storage with KMS-backed encryption
- Syncs around 45,000 transactions a month into Xero, worth over $250 million a year
- I still run and support it in production
Architecture decisions
Designed a centralised, serverless architecture on AWS. Stateless compute via Lambda behind API Gateway. High-throughput, low-latency persistence using DynamoDB. OAuth 2.0 flows implemented using managed identity services. Frontend delivery via CloudFront with automated CI/CD using AWS Amplify.
Legacy Platform Modernisation & Subscription Billing Migration
Rebuilt Fooman's 10-year-old e-commerce platform as technical lead, including domain migration, billing provider replacement and a new React frontend with Cypress browser tests. Active subscriptions and organic search traffic held through the switch.
Legacy Platform Modernisation & Subscription Billing Migration
Rebuilt Fooman's 10-year-old e-commerce platform as technical lead, including domain migration, billing provider replacement and a new React frontend with Cypress browser tests. Active subscriptions and organic search traffic held through the switch. I brought in a contractor with React experience but new to Adobe's PWA Studio and to e-commerce, and mentored them through the build.
Outcomes
- Organic traffic held across a 10-year domain history
- Full order history of 40,000+ orders and all customer accounts carried across
- All active subscriptions migrated, with revenue holding through the switch
- Improved frontend performance and long-term maintainability
- Reduced architectural risk through phased migration
Architecture decisions
Designed a phased migration strategy with rollback points at each stage. Comprehensive 301 redirect mapping to preserve search equity. Built a React frontend consuming a new GraphQL API layer. Cypress browser tests covered the new frontend. Replaced legacy subscription billing provider with no interruption to active recurring revenue.
Payment Gateway Integration & Vendor-Approved Extension
I designed, built and maintained the Magento extension for Payment Express (now Windcave) for eight years. Merchants needed to take card payments without handling card data, and to ship only orders that had actually been paid. It became the most widely used Payment Express integration for Magento at the time.
Payment Gateway Integration & Vendor-Approved Extension
I designed, built and maintained the Magento extension for Payment Express (now Windcave) for eight years. Merchants needed to take card payments without handling card data, and to ship only orders that had actually been paid. It became the most widely used Payment Express integration for Magento at the time.
Outcomes
- 1,600+ downloads – the most widely used Payment Express extension for Magento at the time
- Tested and approved by Payment Express
- Card data kept off merchant servers, reducing merchants' compliance burden
- Four Payment Express integration methods supported in one extension
- Optional Fraud Scoring
Architecture decisions
Order status driven only by Payment Express's server-to-server notification. The customer's browser redirect can be interrupted or altered, so it was ignored. Card data kept off merchant servers – PxPay via a hosted payment page, PxFusion via a checkout iframe submitting directly to Payment Express. Customers stayed on the merchant's site, but the merchant never handled the card. Tokenised billing stored Payment Express tokens, not cards, enabling saved cards and repeat orders. The same token layer later supported a custom subscription billing build outside the public release. 3D Secure via the Web Service integration, adding card-holder authentication without a gateway change. Refunds processed from the Magento admin, and Maxmind fraud screening on direct card payments. Payment-specific order statuses separated pending, authorised and paid orders for fulfilment teams. Payment links for orders taken outside the checkout. Free edition published through MageBase, a New Zealand Magento developer collective; Pro edition released under Fooman.
Multi-Product Portfolio Engineering
Designed, built and maintained a production software portfolio spanning 18+ products with lifecycles exceeding 10 years – used by brands including Panasonic, Les Mills, Weta Workshop, Flybuys, PGG Wrightson, Guinness and Nespresso, and deployed in 160+ countries.
Multi-Product Portfolio Engineering
Designed, built and maintained a production software portfolio spanning 18+ products with lifecycles exceeding 10 years – used by brands including Panasonic, Les Mills, Weta Workshop, Flybuys, PGG Wrightson, Guinness and Nespresso, and deployed in 160+ countries.
Outcomes
- Sustained 5-star average ratings across the portfolio over 10+ years
- Merchants stayed because things kept working – even through multiple major platform overhauls
- Products evolved alongside the platform without breaking what merchants were already running
- Managed deliberate end-of-life and deprecation decisions when products reached the end of their useful lifespan
Architecture decisions
Defined and maintained engineering standards across the entire portfolio – not just for initial development but for ongoing maintenance across 10+ year product lifecycles. Standardised CI/CD pipelines and Docker-based local development environments. Designed plugin-oriented, upgrade-safe architectures that absorbed major platform changes without breaking merchant stores. Managed version compatibility matrices across 18+ products, multiple platform versions, and PHP version requirements simultaneously. Made deliberate backward-compatibility guarantees – and honoured them across years of platform evolution.
What Clients Say
We are using Kristof's software for quite a few years now. They work reliably and the quality is consistently high.
Sebastian, Director Architecture & Strategy, digital commerce agency
I contacted Kristof as we needed a way to charge a fee on orders depending on payment method. He understood the problem immediately and provided a clean solution that worked perfectly for our setup.
Ellen, Director, international retailer
I will definitely recommend your software to our subsidiaries, I've never seen such a perfectly coded extension and excellent support.
Eduard, Full-Stack Developer, German consortium
Proven Track Record
Founder & Lead Engineer – Fooman
I founded Fooman in 2008 and have engineered its products since. It is a product software company for e-commerce, payments and business system integrations, across the Adobe Commerce (Magento), Xero, Payment Express (now Windcave) and Vend (now Lightspeed) ecosystems. Fooman is a technology partner to Adobe Commerce and Xero, so my code had to meet their certification requirements and release cycles. I wrote, deployed and supported the software myself, so the problems I saw in production shaped how I built the next thing.
Product Engineering: Wrote and maintained 18+ commercial products in PHP and Node.js, with more than 200,000 downloads and 257 five-star reviews. They are deployed world-wide and used by brands including Panasonic, Les Mills, Weta Workshop, Flybuys, PGG Wrightson, Guinness and Nespresso. I built for upgrade safety and long-term maintainability, to keep technical debt away from merchants.
Cloud Architecture & Serverless Delivery (AWS): Built a serverless Node.js platform on Amazon Web Services – Lambda, DynamoDB, API Gateway, CloudFront, KMS – achieving ~89% reduction in monthly infrastructure cost and horizontal scalability with zero capacity planning. I chose serverless over containers because demand was spiky. The platform scales with load and charges only for use, replacing a flat monthly cost per server. That decision is where the cost reduction came from. Beyond this project, I have worked across a broad range of AWS services including ECS/Fargate, EFS, Aurora Serverless, EventBridge, and SSM Parameter Store – with a focus on understanding the cost model and operational trade-offs of each service rather than defaulting to the most familiar option.
Platform Modernisation & Migration: Rebuilt Fooman's 10-year-old e-commerce platform, including domain migration, subscription billing replacement and a new React frontend on a GraphQL API. Search traffic and revenue held through the switch. I brought in a contractor with React experience but new to Adobe's PWA Studio and to e-commerce, and mentored them through the build.
Platform Integration: Designed and built integration architecture connecting e-commerce platforms with Xero accounting – including OAuth 2.0 authentication flows, encrypted token storage, and secure API communication. The platform syncs around 45,000 transactions a month into Xero, worth more than $250 million a year.
Platform Collaboration & Ecosystem Leadership: Collaborated directly with Magento/Adobe Commerce as a Technology Partner. Founded and led ExtDN, aligning up to 20 independent extension companies on shared quality standards without formal authority.
Team Leadership, Code Review & Mentoring: Led a distributed team of up to six part-time contractors across development, support, marketing and finance. Reviewed code for and mentored the developers, and set the standards they worked to: code quality, CI/CD pipelines, Docker-based development environments and documentation.
Production Ownership: Maintained production systems serving merchants in 160+ countries with sustained 5-star ratings. I handled technical support myself, so I saw first-hand how my code behaved in production. Built solutions that survived multiple major platform overhauls – when the platform shipped breaking changes, the products kept running. Every product supported multiple Adobe Commerce and PHP versions at once, with automated tests run against each supported combination.
Current Availability: The business now runs with little day-to-day input, so I am available full-time for a new role, contract or permanent.
Earlier Technical & Operational Experience
- Ran operations for the Skinit business unit at Telegistics, Auckland, handling merchandising logistics across Telecom New Zealand's (now Spark) national retail network. Introduced new business procedures and built the content management system for the Telegistics website.
- Merchandising co-ordinator in Telecom New Zealand's merchandising team, Auckland, supporting Telecom Mobile retail stores nationwide.
- 3D compositing and technical animation at q~bus Mediatektur in Berlin for client Deutsche Telekom, including high-profile media installations at Germany's biggest tech expo.
- Contract web development for clients including the German Institute for International and Security Affairs.
Recent Technology Projects
- Sympozium (open source; Go, Kubernetes, AI agents): contributed to a Kubernetes-native platform for running AI agents, working in Go with AI coding agents. Delivered harness mode, which runs external agent harnesses on the platform and rejects runs that ask for features a harness cannot support. Added gate-driven retries, so a run that fails a quality check reruns without losing track of its delegations, schedules or callers. Also built file-editing and context-management tools for the agent runtime.
- Property price tracker (TypeScript, Node.js, MCP, GitHub Actions): built a Trade Me property price tracker with AI coding agents working from GitHub issues, test-first. It includes its own MCP server so AI assistants can query the data.
- Health app (Swift, Apple HealthKit, AWS Bedrock): built an iOS app that reads Apple Health data and adds AI features through AWS Bedrock.
International conference speaker (2012 – 2019) on topics including extensible platform architecture, dependency management, and reliable delivery at scale. Conferences include Magento Imagine (USA), Magento Live (UK and Australia), and New Zealand and European industry events.
Recognised as a Magento Master (2016 – 2018) – 1 of 20 worldwide for three consecutive years – recognised by Magento for sustained technical leadership, platform architecture expertise, and ecosystem contribution.
This experience shapes how I work as an engineer: code that survives platform change, safe modernisation, and standards that let a team ship with confidence.
Industry
Recognition
Why Work With Me
Deep experience, low ramp-up: I can look at a system and have a pretty good idea of what is going on quickly – whether that is tracing a production issue through a stacktrace or diagnosing why a server configuration is silently corrupting file attachments. I do not need long onboarding periods to start contributing.
Practical, not theoretical: Every technical decision ties back to a business problem. I have shipped production code used worldwide – reliability is not an aspiration, it is what I have been delivering.
Technical communication: I am the person in the room who can explain the trade-off to the person paying for it and to the team building it.
Full-lifecycle ownership: I have owned everything from initial solution design through to production support. That end-to-end responsibility covers architecture, delivery and operations, so operational reality shapes the design from the start.
Proven across the full stack: I have designed serverless platforms on AWS, migrated legacy systems without downtime, built third-party integrations from authentication through to data sync, and maintained a production software portfolio for over a decade.
Available for Contract or Permanent Roles
I am available now for contract or permanent Senior Software Engineer roles, where 15+ years of building and running production systems makes a real difference.
Whether it is Node.js and AWS serverless, integrations or platform modernisation, I am happy to have a chat.