Add hackathon summary for 2026-03 (#960)

* docs(hackathon): Add images for 2026-03

* docs(hackathon): Add summary for 2026-03

* docs(hackathon): Update index entry for 2026-03

* docs(hackathon): Remove loadbalancers for provider-local topic as it was out of scope (PR review)

* docs(hackathon): Use smaller images (PR review)

Author: marc1404

website/community/hackathons/2026-03.md

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+---
+title: March 2026
+weight: -202603
+outline: 2
+---
+
+# Hack The Garden Sofia Edition 03/2026 Wrap Up
+
+- 🗓️ **Date:** 16.03.2026 – 20.03.2026
+- 📍 **Location:** [SAP Center Sofia](https://maps.app.goo.gl/SPdvQ4F2p7Qqfx4p9)
+- 👤 **Organizer:** [SAP](https://www.sap.com/)
+- 📘 **Topics:** [hackathon/discussions#41](https://github.com/gardener/hackathon/discussions/41)
+
+![Group picture of the hackathon attendees on the rooftop of the SAP Center Sofia](./images/2026-03/group-picture.jpeg)
+
+## 🐳 [GEP-28] Self-Hosted Shoot: Gardener-in-Docker (`gind`)
+
+> [!TIP]
+> You can find out more about [Self-Hosted Shoot Clusters in GEP-28](https://github.com/gardener/enhancements/blob/main/geps/0028-self-hosted-shoot-clusters).
+
+> **Tracking:** [hackathon#8](https://github.com/gardener/hackathon/issues/8)
+
+### Problem Statement
+
+It should be possible to create self-hosted shoot clusters using `gardenadm` and run Gardener inside such a cluster.
+Before introducing a tool like `gind` (which runs the self-hosted shoot directly in Docker), we first need to support hosting Gardener inside a self-hosted shoot cluster.
+
+### Achievements
+
+* Deployed `gardener-operator` into the self-hosted shoot.
+* Deployed a `Garden` resource — the self-hosted shoot now serves as runtime cluster for the virtual garden.
+* Enabled the `ManagedSeed` controller in the shoot `gardenlet`, allowing the self-hosted `Shoot` itself to be referenced in the `ManagedSeed`.
+* Adapted the local setup for direct API access to both the self-hosted shoot API server and the virtual garden API server from the host machine (no port-forwarding).
+
+### Next Steps
+
+* Cleanup the code and commits, adapt documentation and `make` rules.
+* Open individual PRs for the different features and get them merged.
+* Introduce an e2e test for this scenario ("fully self-contained Gardener").
+* Try spinning up workerless and regular hosted shoots on this seed.
+
+### Code & Pull Requests
+
+* [Don't create duplicate `ControllerInstallation`s when self-hosted `Shoot` is also a `Seed` – gardener/gardener#14282](https://github.com/gardener/gardener/pull/14282)
+* [Ensure all system pods run on system component nodes – gardener/gardener#14367](https://github.com/gardener/gardener/pull/14367)
+* [`gardenadm connect`: Enable `ManagedSeed` controller in `gardenlet` – gardener/gardener#14369](https://github.com/gardener/gardener/pull/14369)
+* [Make self-hosted shoot API server accessible from host machine - gardener/gardener#14370](https://github.com/gardener/gardener/pull/14370)
+* [Enable deployment of `gardener-operator` (and `Garden`) inside self-hosted `Shoot`s – gardener/gardener#14387](https://github.com/gardener/gardener/pull/14387)
+* [Introduce GinD (Gardener-in-Docker) dev setup for self-hosted `Shoot`s w/ unmanaged infra – gardener/gardener#14700](https://github.com/gardener/gardener/issues/14700)
+* [Create `ManagedSeed` for self-hosted `Shoot` to promote it to seed cluster – gardener/gardener#14747](https://github.com/gardener/gardener/pull/14747)
+
+## 🕹️ [GEP-28] Ensure System Pods Run on Control Plane Nodes
+
+> **Tracking:** [hackathon#16](https://github.com/gardener/hackathon/issues/16)
+
+### Problem Statement
+
+System components in a self-hosted shoot (pods in `garden` namespace, extensions, system pods in `kube-system`) are not guaranteed to run exclusively on control plane nodes.
+Over time, they might get rescheduled to worker nodes.
+
+### Achievements
+
+* Implemented placement enforcement so that system pods exclusively run on control plane nodes.
+
+### Code & Pull Requests
+
+* [Ensure all system pods run on system component nodes – gardener/gardener#14367](https://github.com/gardener/gardener/pull/14367)
+
+## ❤️‍🩹 [GEP-28] Self-Hosted Shoot Control Plane Restoration
+
+> **Tracking:** [hackathon#22](https://github.com/gardener/hackathon/issues/22)
+
+### Problem Statement
+
+When a self-hosted shoot cluster loses its control plane, it must be possible to restore the secrets and control plane state from the `ShootState` resource.
+
+### Achievements
+
+* PoC branch using the `ShootState` for restoring secrets when restoring a control plane of a self-hosted shoot: [poc/gep-28-dr](https://github.com/ialidzhikov/gardener/commits/poc/gep-28-dr/).
+* Demo scripts: [demo/restore-from-shootstate](https://github.com/ialidzhikov/gardener/commits/demo/restore-from-shootstate/).
+* Fixed a bug when computing the ShootState for a self-hosted shoot cluster.
+
+### Next Steps
+
+* Eliminate hacks/workarounds: enable etcd encryption, adapt csrapprover for gardener-node-agent CSRs, fix pod network availability check, sanitize etcd data, eliminate second-phase restore.
+* Design and implement how to read/compute the ShootState (via `gardenadm discover` or from etcd backup).
+* Design and implement etcd backup restore.
+* Add support for restoring a self-hosted shoot with worker nodes.
+
+### Code & Pull Requests
+
+* [Fix ShootState resource deployment for a self-hosted Shoot – gardener/gardener#14339](https://github.com/gardener/gardener/pull/14339)
+
+## 🗝️ [GEP-28] Eliminate Static Admin Token After `gardenadm connect`
+
+> **Tracking:** [hackathon#14](https://github.com/gardener/hackathon/issues/14)
+
+### Problem Statement
+
+After `gardenadm init`, the control plane components use a static token with cluster-admin privileges for bootstrapping.
+Once the cluster is fully connected (`gardenadm connect`), this should be replaced with short-lived tokens from `gardener-resource-manager`.
+
+### Outcome
+
+Discussed and decided that this will be part of the `shoot/shoot` controller and should not be handled in `gardenadm init` or `gardenadm connect` explicitly.
+Closed in favor of [Experiment with `shoot/shoot` controller in Self-Hosted Shoot Clusters – hackathon#45](https://github.com/gardener/hackathon/issues/45).
+
+## 🔑 Functional Local Setup with Workload Identity
+
+> **Tracking:** [hackathon#28](https://github.com/gardener/hackathon/issues/28)
+
+### Problem Statement
+
+The local development setup does not work with Workload Identity (WI), making it impossible to test WI-dependent scenarios locally.
+
+### Achievements
+
+* Initial implementation establishing trust between the local KinD cluster and the Gardener Workload Identity Issuer.
+* Identified that Machine Controller Manager is not deployed with minimal permissions — opened a PR to address this.
+
+### Next Steps
+
+* Clean up the code in the linked branch.
+* Verify all scenarios work as expected and current tests pass.
+* Implement new e2e tests leveraging Workload Identity or enable it for existing ones.
+* Add support for Workload Identity in other local scenarios (ETCD backups, DNS, etc.).
+
+### Code & Pull Requests
+
+* Branch: [dimityrmirchev/gardener:wi-local-setup](https://github.com/dimityrmirchev/gardener/tree/wi-local-setup)
+* [Reduce MCM permissions – gardener/gardener#14372](https://github.com/gardener/gardener/pull/14372)
+
+## 🤖 AGENTS.md / SKILLS.md for Gardener Repos
+
+> **Tracking:** [hackathon#31](https://github.com/gardener/hackathon/issues/31)
+
+### Problem Statement
+
+AI-native development tools (Claude Code, Codex CLI, Gemini CLI) benefit from repository-level context files (`AGENTS.md`, `SKILLS.md`).
+The question is how to best leverage these for the Gardener ecosystem.
+
+### Achievements
+
+* Researched recent papers: *Evaluating AGENTS.md* (Feb 2026) and *SkillsBench* (Feb/Mar 2026).
+* Key findings: curated skills provide +16.2pp average improvement; LLM-generated context provides negligible or negative benefit; focused skills with 2–3 modules outperform comprehensive documentation.
+* Proposed a minimal `AGENTS.md` template focused on "common mistakes and confusion points" rather than comprehensive documentation.
+
+### Next Steps
+
+* Experiment with proposed `AGENTS.md` file in gardener org repos (not `gardener/gardener`).
+* If significant benefit is observed, present findings in a larger forum (Gardener Review Meeting).
+
+## 📦 PoC: Repo Tools Integration with Extension Repositories
+
+> **Tracking:** [hackathon#18](https://github.com/gardener/hackathon/issues/18)
+
+### Problem Statement
+
+Extension repositories share ~10 almost identical make targets and hack scripts with `gardener/gardener`.
+Changes to these shared scripts result in copy-paste effort across all repositories (~20 PRs for a single fix).
+
+### Achievements
+
+* Explored a subtree approach for centralizing shared make targets and hack scripts into a separate repository.
+* Adapted `gardener-extension-shoot-rsyslog-relp` and `pvc-autoscaler` as PoC repositories.
+
+### Next Steps
+
+* Adapt additional repositories to validate the approach and catch problems early.
+* Gather feature requests based on newfound use cases.
+
+## ✅ Diki as a Service
+
+> **Tracking:** [hackathon#24](https://github.com/gardener/hackathon/issues/24)
+
+### Problem Statement
+
+[Diki](https://github.com/gardener/diki) compliance checks should be schedulable, exportable, and operable as a service rather than one-off CLI runs.
+
+### Achievements
+
+* Merged previous work (first PoC and `diki-exporter`) into a working operator: [hackathon-poc branch](https://github.com/georgibaltiev/diki-operator/tree/hackathon-poc).
+* Implemented Postgres exporter in `diki-exporter`.
+* Made the operator capable of running in a different cluster than the `ComplianceScan`s (needed for seed/shoot-namespace topology).
+* PoC'ed `ScheduledComplianceScan`s — spawns scans based on a cron expression.
+
+### Next Steps
+
+* More testing and cleanup.
+* Pour the work into a Gardener extension.
+
+## 🧩 Extension: Generic Shoot Pack (CloudNativePG et al.)
+
+> **Tracking:** [hackathon#19](https://github.com/gardener/hackathon/issues/19)
+
+### Problem Statement
+
+Installing upstream operators into shoot clusters requires repetitive per-operator extension development.
+A generic packaging mechanism would reduce this overhead.
+
+### Achievements
+
+* Developed [gardener-extension-shoot-pack](https://github.com/dnaeon/gardener-extension-shoot-pack/tree/feat/initial) — a generic Gardener extension that uses package specifications to install operators as managed resources.
+* Ships packages for: cert-manager, CloudNativePG, Prometheus Operator, and Valkey Operator.
+* Tooling available to inspect, view, and create new package specs.
+
+### Next Steps
+
+* Clean things up.
+* Add more tests.
+
+## 🪣 Fix Leaking ValidatingWebhookConfigurations in (Virtual-)Garden
+
+> **Tracking:** [hackathon#21](https://github.com/gardener/hackathon/issues/21)
+
+### Problem Statement
+
+When deploying extensions via `gardener-operator` using `extensions.operator.gardener.cloud` resources, `ValidatingWebhookConfiguration`s remain in the virtual-garden cluster even after removing the extension.
+The root cause: the `--webhook-config-owner-namespace` option defaults to `garden` namespace, preventing proper garbage collection.
+
+### Achievements
+
+* Identified the root cause — missing `--webhook-config-owner-namespace` flag in extension admission deployments.
+* A fix existed since ~2 years ([Cleanup webhook configuration from virtual cluster when removing admission deployment – gardener/gardener#10585](https://github.com/gardener/gardener/pull/10585)) but was not adopted by all extensions.
+* Opened umbrella issue to track fixes across all affected extensions.
+
+### Next Steps
+
+* Apply the `--webhook-config-owner-namespace` option to each affected extension's admission deployment.
+
+### Code & Pull Requests
+
+* [Fix leaking of `validatingwebhookconfiguration` resources in extensions – gardener/gardener#14334](https://github.com/gardener/gardener/issues/14334)
+
+## 📡 Resolve the Istio Metrics Leak
+
+> **Tracking:** [hackathon#12](https://github.com/gardener/hackathon/issues/12)
+
+### Problem Statement
+
+Istio sidecar metrics for terminated pods accumulate indefinitely, leading to unbounded cardinality in Prometheus.
+
+### Achievements
+
+* Configured Istio metric rotation via environment variables (`METRIC_ROTATION_INTERVAL`, `METRIC_GRACEFUL_DELETION_INTERVAL`).
+* Verified correct behavior: after rotation interval, old pod metrics disappear and new pod metrics appear; long-lived connection metrics reset correctly (counters restart from 0, compatible with PromQL `rate` functions).
+* Fixed duplicate scraping caused by two Istio services (`istio-gateway` LoadBalancer and `istio-gateway-internal` ClusterIP) matching the same ServiceMonitor label selector.
+
+### Next Steps
+
+* The env-var approach is deprecated from Istio v1.28+.
+* Migration to annotation-based configuration (`SidecarStatsEvictionInterval`) will be needed when upgrading beyond v1.27.
+
+### Code & Pull Requests
+
+* [Evict stale Istio Gateway metrics and reenable scraping – gardener/gardener#14337](https://github.com/gardener/gardener/pull/14337)
+
+---
+
+![Rooftop view from the SAP Center Sofia towards Vitosha mountain](./images/2026-03/sofia-bg.jpeg)
+
+---
+
+![ApeiroRA – Funded by the European Union NextGenerationEU](https://apeirora.eu/assets/img/BMWK-EU.png)

website/community/hackathons/_index.md

@@ -14,6 +14,7 @@ If you feel like you can contribute something, you are encouraged to file a PR.
 | Date                    | Location                                                                        | Organizer | Wrap Up                 |
 |:------------------------|:--------------------------------------------------------------------------------|:----------|:------------------------|
 | 04.05.2026 – 08.05.2026 | [Schlosshof Freizeitheim, Schelklingen](https://www.schlosshof-info.de/)        | x-cellent | [Summary](./2026-05.md) |
+| 16.03.2026 – 20.03.2026 | [SAP Center Sofia](https://maps.app.goo.gl/SPdvQ4F2p7Qqfx4p9)                   | SAP       | [Summary](./2026-03.md) |
 | 08.12.2025 – 12.12.2025 | [SAP Center Walldorf](https://maps.app.goo.gl/L3Yv7jooK9kfsaxb9)                | SAP       | [Summary](./2025-12.md) |
 | 24.11.2025 – 28.11.2025 | [Schlosshof Freizeitheim, Schelklingen](https://www.schlosshof-info.de/)        | x-cellent | [Summary](./2025-11.md) |
 | 21.07.2025 – 25.07.2025 | [SAP Center Sofia](https://maps.app.goo.gl/SPdvQ4F2p7Qqfx4p9)                   | SAP       | [Summary](./2025-07.md) |