Kristof Ringleff
Hands-on technical leadership for systems that connect, scale and keep running.
For 18 years I have taken software from business need to production. I set engineering standards, write production code and stay accountable for how it runs.
My work centres on AWS serverless, e-commerce, payments and financial data. I re-architected a production platform onto AWS serverless in eight weeks, cutting infrastructure cost by around 89%. It now syncs transactions worth over $250 million a year into Xero.
Core Competencies
Cloud & Infrastructure
Languages & Frameworks
E-commerce & Platforms
Engineering & Architecture
Ways of Working
AI-Assisted Development
What I Bring
Technical direction
I make the architecture calls and explain the trade-offs behind them, to the people paying and the people building. Years of real platform version changes have shown me which choices survive them and which do not.
Engineering standards and team leadership
I set the standards a team builds to: CI/CD pipelines, automated testing, Docker-based development environments and upgrade-safe architecture. I review code and mentor developers. These standards kept 18+ products running across more than ten years of platform change.
Modernisation and integration
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 re-architected our Xero integration platform from the ground up 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 re-architected our Xero integration platform from the ground up 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
Architecture decisions
Designed a centralised, serverless, event-driven 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
Led the end-to-end solution design for migrating Fooman's 10-year-old e-commerce platform - including domain migration, billing provider replacement, and frontend modernisation - without disrupting active subscriptions or organic search traffic.
Legacy Platform Modernisation & Subscription Billing Migration
Led the end-to-end solution design for migrating Fooman's 10-year-old e-commerce platform - including domain migration, billing provider replacement, and frontend modernisation - without disrupting active subscriptions or organic search traffic.
Outcomes
- Zero loss of organic traffic across a 10-year domain history
- Full order history of 40,000+ orders and all customer accounts carried across
- Seamless migration of all active subscriptions with no revenue disruption
- 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. Introduced React-based frontend consuming a GraphQL API layer. 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.
Platform Ecosystem Architecture & Product Governance
Designed and governed 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.
Platform Ecosystem Architecture & Product Governance
Designed and governed 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
Principal Engineer & Founder/Director - Fooman
I founded Fooman and set its technical direction. 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. I built it into a technology partner to Adobe Commerce and Xero, engineering within their certification requirements and release cycles. I owned architecture, delivery and production operations, so the problems I saw in production shaped my next architecture decisions.
Architecture & Technical Direction: Designed and evolved a portfolio of 18+ production software products with more than 200,000 downloads and 257 five-star reviews, deployed world-wide and used by brands including Panasonic, Les Mills, Weta Workshop, Flybuys, PGG Wrightson, Guinness and Nespresso. Made all architecture decisions - prioritising scalability, upgrade safety, and long-term maintainability to minimise technical debt for end-users.
Cloud Architecture & Serverless Delivery (AWS): Designed and delivered a serverless, event-driven SaaS 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: Led the migration of Fooman's 10-year-old e-commerce platform including domain migration, subscription billing replacement, and frontend modernisation (React, GraphQL). Delivered with zero SEO impact and no revenue disruption.
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 over $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. Recognised as a Magento Master (2016–2018) - 1 of 20 worldwide for three consecutive years - for sustained technical leadership and contribution to platform architecture standards.
Technical Team Leadership: Built and led a distributed team of six part-time contractors. Set the standards developers worked to, reviewed their code and mentored them. Made the architecture decisions they built on, and explained the trade-offs behind them. Established engineering standards for 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. Built solutions that survived multiple major platform overhauls - when the platform shipped breaking changes, the products kept running.
Current Availability: The business now runs with minimal day-to-day input, so I am fully available for a new role, contract or permanent.
Earlier Technical & Operational Experience
- Production management for the Skinit business unit at Telegistics/Telecom (now Spark), coordinating large-scale merchandising logistics across Telecom's national retail network.
- 3D compositing and technical animation at q-bus Mediatektur in Germany 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
- Agentic development: built a Trade Me property price tracker entirely with AI agents working from GitHub issues, using test-driven development. It includes its own MCP server.
- AWS Bedrock / iOS: built a health app in Swift, integrating Apple Health with AI capabilities 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 a Principal Engineer: extensible platforms, safe modernisation, and standards that let teams deliver with confidence.
Industry
Recognition
Why Work With Me
Technical leadership: I set the standards, review the code and make the architecture calls. I have done it inside my own team, and across 20 independent companies through ExtDN.
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 architecture 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 Principal Engineer roles, where having designed, built and operated production systems for 18 years makes a real difference.
Whether it is cloud architecture, platform modernisation, integration or raising your team's engineering standards, I am happy to have a chat.