Dr. Stefan Schimanski sttts

Stefan Schimanski 👋

I build software: developer tools, distributed systems, experiments, side projects, and the occasional weird machine.

Publicly, that currently looks like:

A lot of my work happens upstream rather than only in personal repos.

SIG API Machinery lead and maintainer for many years; represented the SIG at KubeCon — 📺 2018, 📺 2019, 📺 2021, 📺 2023, 📺 2026
co-authored the foundational CRD improvements 2018–2022: structural schemas (OpenAPI-based type system), pruning, defaulting, webhook conversion — turning CRDs from a prototype into production-grade infrastructure
co-designed Watch List (KEP-3157) — streaming informer startup replacing LIST, reducing server-side memory from terabytes to gigabytes in large clusters; critical for AI/ML workloads
drove generic control plane (KEP-4080) — extracting kube-apiserver into an embeddable library, enabling projects like kcp to build real control planes on top
maintained kube-openapi — the go-openapi fork backing Kubernetes's OpenAPI aggregation pipeline
co-authored audit logging in the Kubernetes API server (2017–2018)
implemented deepcopy code generation (used across the entire Kubernetes codebase today) — replaced reflect-based copying with generated typed code, significantly improving memory efficiency and runtime reliability
co-created the Kubernetes codebase structure of hierarchical staging repos (client-go, apimachinery, api, apiserver, …) — made the codebase significantly more maintainable and enabled its continued growth
built the publishing-bot staging build machinery — the system that publishes Kubernetes staging repos (client-go, apimachinery, etc.) as independent Go modules; still running today, including go.mod support

architectural lead during the Red Hat era; helped transition the project into CNCF Sandbox; still project advisor
designed the core multi-tenancy model: APIExport and APIBinding — CRDs defined once, bound into many workspaces without copying, forming the basis for a new kind of platform API
drove the authorization model: workspace-scoped RBAC, user scopes, and warrants for cross-workspace delegation
built the virtual workspace layer and the sharded cache server for replication across kcp instances
kcp was the main real-world driver for the generic control plane work and directly influenced kube-bind and multicluster-runtime

control plane lead for several years, owning the reliability and lifecycle of the OpenShift API server tier
designed the static pod installer model in library-go: revision-based rolling updates for API servers with startup monitors, fallback logic, and prune policies — zero downtime
owned the kube-apiserver operator and the OpenShift apiserver operator end-to-end
drove KMS encryption at rest for the OpenShift API server, integrating Kubernetes's KMS envelope encryption with OpenShift's key management
did multiple rebases of the OpenShift codebase onto new Kubernetes versions, keeping a large downstream fork aligned with fast-moving upstream
production issues in OpenShift fed back into SIG API Machinery work upstream, and vice versa

Contributions across Crossplane and related projects — Go

🧠 nanoschnack — language model training and tokenizer work — Python, Go — 📺 KubeCon
🕸️ kausality — causal traceability for Kubernetes resource mutations — Go — 📺 KubeCon
🔗 kube-bind — invented CRD binding across Kubernetes clusters — Go — 📺 KubeCon — 📺 ContainerDays
🌐 multicluster-runtime — invented and bootstrapped multi-cluster controller-runtime — Go — 📺 KubeCon
🤖 slagent — Claude talking to Slack — Go
☸️ kc — Kubernetes Commander — Go
🌐 kubectl-http — HTTPie as a kubectl plugin — Shell
🕹️ claw64 — an OpenClaw-inspired Claw for the Commodore 64 — Go
🧩 xf-cli — XenForo CLI and MCP tooling — Go
🧪 shell-ai-widget — AI-powered inline shell command editing — Go
🏠 ha-git-backup — Git-backed backup add-on for Home Assistant — Shell
🎮 kbounce — Godot recreation of KBounce — GDScript — Web — App Store
⚡ godot-quickjs — QuickJS embedded into Godot 4 — C++
🔧 crd-gates — feature gates for CRDs — Go
🧱 blender-wrl — Blender plugin for importing WRL files — Python
📚 tvniki — a revived programming learning system from 1996 — Pascal

All talks: YouTube

Older projects and ecosystems that still represent what I build:

🐧 KDE — core contributor: KBounce, KMixer, Konqueror, browser plugins, and khtml, later becoming WebKit by Apple and today used in nearly every browser — C++, Qt
☁️ Kubermatic — invented Kubermatic, predecessor to Cluster API and HyperShift, later sold to Loodse, today Kubermatic GmbH — Go
⚙️ elastic-etcd — elastic discovery wrapper around etcd — Go
🐳 kubernetes-dind-cluster — early Docker-in-Docker Kubernetes dev clusters, an ancestor of kind — Shell
🏗️ compute-platform — Mesos-based compute platform — Shell
🚀 kubernetes-mesos — Kubernetes on Apache Mesos — Go
🏃 Marathon — container orchestration on Apache Mesos — Scala
🛰️ mesos-dns — DNS-based service discovery for Mesos — Go
📧 ldap-notify — LDAP password and login expiration notifications — Python
🗺️ google-maps-mock — Google Maps JS mocking for tests — JavaScript