Notes on AI agents, platform engineering, and running things on hardware I own.https://blog.kellerstein.org/https://blog.kellerstein.org/blog/hello-world/https://blog.kellerstein.org/blog/hello-world/Placeholder post — the blog is live, real articles land here next.Mon, 27 Jul 2026 00:00:00 GMThttps://blog.kellerstein.org/blog/formatting-reference/https://blog.kellerstein.org/blog/formatting-reference/Example post exercising every Markdown element the theme styles.Sun, 26 Jul 2026 00:00:00 GMThttps://blog.kellerstein.org/blog/drag-a-div-get-a-diff/https://blog.kellerstein.org/blog/drag-a-div-get-a-diff/VEX turns browser gestures into source-code changes. Three hard problems hide in that sentence — here is what each one taught me.Tue, 14 Jul 2026 08:29:44 GMThttps://blog.kellerstein.org/blog/it-works-from-the-terminal/https://blog.kellerstein.org/blog/it-works-from-the-terminal/The app ran perfectly when I launched it from a shell and failed with ENOENT when a user double-clicked it. A GUI app does not have your PATH, and the only thing that knows your PATH is your shell.Sun, 21 Jun 2026 13:12:32 GMThttps://blog.kellerstein.org/blog/six-hundred-lines-or-it-does-not-ship/https://blog.kellerstein.org/blog/six-hundred-lines-or-it-does-not-ship/A 2,313-line orchestrator with a 1,073-line function is maintainable by a human with an IDE and unmaintainable by an agent. The refactor whose acceptance criterion was an agent behaviour, the CI guard that enforced it — and the fact that the guard is red as I write this.Tue, 26 May 2026 00:00:00 GMThttps://blog.kellerstein.org/blog/i-built-a-time-machine-then-deleted-half-of-it/https://blog.kellerstein.org/blog/i-built-a-time-machine-then-deleted-half-of-it/Four timeline verbs, parallel variants in git worktrees, a record mode and five branch families. Two cleanup specs removed almost all of it — including, awkwardly, the feature whose existence justified the first round of deletions.Tue, 12 May 2026 00:00:00 GMThttps://blog.kellerstein.org/blog/three-counters-three-answers/https://blog.kellerstein.org/blog/three-counters-three-answers/One Stop click produced a UI, a state file and a git history that disagreed with each other three different ways. None of them was wrong. The reconciliation point that should have caught it was a line in a spec that said "details TBD in implementation".Tue, 28 Apr 2026 00:00:00 GMThttps://blog.kellerstein.org/blog/your-test-suite-bills-by-the-token/https://blog.kellerstein.org/blog/your-test-suite-bills-by-the-token/Twenty minutes and real dollars to verify a two-line UI change. A pluggable agent backend, a mock that refuses to improvise, and checkpoint replay took it to sixty seconds and zero — plus an honest account of what the mock does not buy you.Tue, 21 Apr 2026 00:00:00 GMThttps://blog.kellerstein.org/blog/nine-stages-nine-amnesiacs/https://blog.kellerstein.org/blog/nine-stages-nine-amnesiacs/Dex builds a project unattended by making sure no agent ever remembers anything. State travels through the filesystem instead — which works beautifully for artifacts and catastrophically for decisions.Sun, 19 Apr 2026 00:00:00 GMThttps://blog.kellerstein.org/blog/the-agent-spawned-an-agent-and-i-could-not-see-it/https://blog.kellerstein.org/blog/the-agent-spawned-an-agent-and-i-could-not-see-it/A subagent is a black box that spends your money. Making it inspectable took no new instrumentation at all — the events were already firing, into nothing.Tue, 14 Apr 2026 23:45:19 GMThttps://blog.kellerstein.org/blog/six-polling-loops-and-a-spinning-fan/https://blog.kellerstein.org/blog/six-polling-loops-and-a-spinning-fan/VEX was idle and my laptop was audible. The fix was not "poll slower" — it was noticing that a UI which asks "anything new?" sixty times a minute is a UI with no idea what happened.Tue, 07 Apr 2026 17:11:56 GMThttps://blog.kellerstein.org/blog/the-field-that-was-never-populated/https://blog.kellerstein.org/blog/the-field-that-was-never-populated/Continuing a conversation with an agent that already finished turned out to be one line of SDK config and three days of admitting my data model thought agents were disposable.Sun, 05 Apr 2026 19:56:25 GMThttps://blog.kellerstein.org/blog/the-model-was-the-easy-part/https://blog.kellerstein.org/blog/the-model-was-the-easy-part/A retrospective on OpenOperator. What I would keep, what I would redo, and why a commit called "remove hardcoded API keys" landing a year late is the most honest thing in the history.Fri, 20 Mar 2026 00:00:00 GMThttps://blog.kellerstein.org/blog/benchmarking-ai-agents-at-scale/https://blog.kellerstein.org/blog/benchmarking-ai-agents-at-scale/Five workload classes with five different scaling shapes, a bounded queue that fans tests into Kubernetes Jobs, and the reason your autoscaler makes terrible decisions about 30 GB virtual machines.Wed, 04 Jun 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/one-proxy-pod-per-vm/https://blog.kellerstein.org/blog/one-proxy-pod-per-vm/A design that is obviously right at n=1 and obviously wrong at n=20, with no warning in between. The commit that deleted it is the best one in the repository.Thu, 01 May 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/streaming-helm-to-a-browser/https://blog.kellerstein.org/blog/streaming-helm-to-a-browser/Provisioning a VM takes three minutes. A spinner is not an acceptable answer. An async generator, a path-keyed WebSocket relay, and one design decision I would not repeat.Wed, 30 Apr 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/volumesnapshots-as-golden-images/https://blog.kellerstein.org/blog/volumesnapshots-as-golden-images/One Helm chart, two completely different storage topologies behind a single boolean. Plus the two bugs it cost — a StatefulSet naming convention and a substring match that matched too much.Tue, 22 Apr 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/reading-teams-telemetry-microsoft-bond/https://blog.kellerstein.org/blog/reading-teams-telemetry-microsoft-bond/Ground truth from an application with no test hooks. mitmproxy local mode against a single process, a hand-written Bond Compact Binary decoder, and the one-line AKS bug that killed a day.Sun, 20 Apr 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/shipping-a-6gb-iso-to-every-pod/https://blog.kellerstein.org/blog/shipping-a-6gb-iso-to-every-pod/An initContainer that pulls once, one PVC projected into eleven mount points via subPath, and a three-month migration from a storage key to workload identity.Wed, 16 Apr 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/kvm-in-a-kubernetes-pod/https://blog.kellerstein.org/blog/kvm-in-a-kubernetes-pod/hostPath /dev/kvm, privileged: true, and the Deployment→StatefulSet migration. Plus the annotation that stops the autoscaler evicting a forty-minute Windows install.Tue, 08 Apr 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/mcp-for-mouse-and-keyboard/https://blog.kellerstein.org/blog/mcp-for-mouse-and-keyboard/Six tools, one resource, and a design decision I still think is underrated — the screenshot is not a tool, it is a resource. Plus the reason we composite a cursor into every capture.Fri, 28 Mar 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/it-looked-like-it-worked/https://blog.kellerstein.org/blog/it-looked-like-it-worked/The least trustworthy signal in the system is the agent reporting success. Here is the evaluator we built instead — and the four-word commit that forced a whole second repository into existence.Wed, 26 Mar 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/tasks-as-config-not-code/https://blog.kellerstein.org/blog/tasks-as-config-not-code/A JSON scenario format with lifecycle hooks, so an agent test starts from the same desktop every time — and so the person writing the test does not have to be the person who wrote the agent.Tue, 25 Mar 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/four-agents-in-four-weeks/https://blog.kellerstein.org/blog/four-agents-in-four-weeks/The old_agents/ directory still holds all the corpses. What each generation got wrong, and why most of a computer-use agent is not acting — it is checking whether the last action worked.Sun, 23 Mar 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/bootstrapping-a-windows-guest/https://blog.kellerstein.org/blog/bootstrapping-a-windows-guest/No SSH, no cloud-init, no config management. Just a .bat file, an SMB share the hypervisor provides, and one Task Scheduler flag that decides whether your screenshots are black.Fri, 21 Mar 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/omniparser-as-a-service/https://blog.kellerstein.org/blog/omniparser-as-a-service/Turning a screenshot into a numbered list of clickable things — YOLOv8 for detection, Florence-2 for captions, OCR for text. And why it had to be a server, not a library.Mon, 17 Mar 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/every-vision-model-we-could-get/https://blog.kellerstein.org/blog/every-vision-model-we-could-get/Magma, Llama 3.2 Vision, Gemma 3, Phi-4, GPT-4o, Claude — including feeding a screen recording instead of stills. What actually moved the needle was not the model.Fri, 07 Mar 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/watching-the-robot-work/https://blog.kellerstein.org/blog/watching-the-robot-work/The day we put noVNC in front of the guest, our mean time to diagnosis dropped by an order of magnitude. Failures in computer use are visual.Tue, 04 Mar 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/qemu-in-docker-a-real-windows-vm/https://blog.kellerstein.org/blog/qemu-in-docker-a-real-windows-vm/It is not Windows in a container. It is QEMU in a container with a Windows ISO and an unattended answer file — and the difference is three lines of compose.yml.Mon, 24 Feb 2025 00:00:00 GMThttps://blog.kellerstein.org/blog/the-api-is-the-screen/https://blog.kellerstein.org/blog/the-api-is-the-screen/Why we built an agent that uses Microsoft Teams the way a person does — and why the model turned out to be the easy part.Sat, 22 Feb 2025 00:00:00 GMT