Hetzner runner SKU whitelist: confirm cx53 (AMD EPYC shared, 16 vCPU, 32 GB) is provisionable

[fabapp2]

Background

promptlm-app's acceptance workflow (.github/workflows/acceptance.yml) currently provisions a cx33 Hetzner VM (4 vCPU AMD, 8 GB RAM). The new native-acceptance suite needs to build the Spring Boot 4 webapp with GraalVM native-image, which asks for >6.15 GB during the build-universe phase and OOMs on cx33 during the compile phase (stage 6/8) even with 8 GB swap.

We picked cx53 (AMD EPYC shared, 16 vCPU, 32 GB RAM, 320 GB disk, ~€0.036/h) as the bump target. Reasons:

• Same shared-AMD family as cx33 — snapshot compatibility almost certainly preserved (cx33 → cx53 is a size bump within one family). The org-bake snapshot referenced by HETZNER_RUNNER_SNAPSHOT_ID is the path that matters.
• Cheaper than cpx42 (the dedicated-vCPU AMD variant, ~€0.046/h) with double the RAM. Native-image is memory-bound, not CPU-bound, so the dedicated-vCPU premium buys nothing.
• Not affected by the cx42 Intel-deprecation gotcha — that was the cx42 SKU name specifically (type 106). The cx5x tier is on the current AMD line.

PR promptLM/promptlm-app#390 flips server_type: cx33 → server_type: cx53.

Asks

• Confirm cx53 is acceptable under any org-wide SKU policy / quota / billing alert in this repo. If a whitelist exists in docs/hetzner-runners.md, add cx53 (and optionally cx43 / cx63 for future flexibility).
• Confirm the snapshot at HETZNER_RUNNER_SNAPSHOT_ID is compatible with cx53 — Hetzner snapshots are usually portable across SKUs in the same architecture family, so no fresh bake should be needed. If a re-bake is required, schedule it.

Acceptance criteria

1. promptLM/promptlm-app's acceptance workflow on PR #390 (or any subsequent full-profile run) provisions a cx53 successfully and reaches native-image compile without OOM.
2. Cost increase documented in docs/hetzner-runners.md: cx53 = €0.036/h (~€0.018 per ~30-min full-profile run).

Context links

• promptlm-app PR #390 — flips cx33 → cx53
• promptLM/.github#36 — adjacent snapshot-bake work (GraalVM + Playwright pre-install); not blocked on this, but if the bake gets re-rolled it should be exercised on cx53 too.
• Hetzner SKU reference: cx53 = AMD EPYC shared, 16 vCPU, 32 GB RAM, 320 GB disk, fsn1 region.

Note

This issue originally asked for cpx42. After review, cx53 is the better target: cheaper, more RAM, same family as the existing cx33. The body above reflects the final ask.

[fabapp2]

Resolution: cx53 blocked by Hetzner project quota → falling back to cx43

Ask #1 (SKU policy / quota) — answered. cx53 is not currently provisionable. Live runs on promptlm-app#390 hit HTTP 412 "Resource limitation detected" on every create attempt (the Cyclenerd action retried 360×). A 412 resource-limit is the Hetzner project quota (account-level, region-global) — not a per-DC stock-out, which is why an earlier fsn1 → nbg1 switch never helped. The project quota doesn't currently allow a 16-vCPU instance.

Decision: target cx43 (AMD EPYC shared, 8 vCPU / 16 GB / 160 GB) instead of cx53.

• 16 GB clears native-image's >6.15 GB build-universe peak — native-image is memory-bound, not CPU-bound, so 8 vCPU is sufficient.
• Sits under the default project quota, so it provisions without a limit-increase request.
• Cheaper: ~€0.020/h vs €0.036/h for cx53.

To use cx53 later, someone with the HCLOUD_TOKEN project must request a limit increase in the Hetzner Console (account → Limits → Request change → Limit increase) covering 16-vCPU instances. Until then, cx53 stays out of the whitelist's usable set even though the name is valid.

Ask #2 (snapshot compatibility) — confirmed. Hetzner snapshots are project-global; HETZNER_RUNNER_SNAPSHOT_ID is valid across cx33/cx43/cx53 and across regions. No re-bake needed for the cx33 → cx43 bump (same shared-AMD CX family).

Done

• promptlm-app#390: server_type: cx53 → cx43, location: nbg1 → fsn1 (org default), comments corrected to the real root cause.
• This repo's docs/hetzner-runners.md: heavier-SKU cost table (cx33/cx43/cx53, AC ci: add reusable release-java-ghpackages.yml workflow #2) + a troubleshooting entry for the 412 project-quota failure.

Follow-ups (not blocking this issue)

1. AC ci: add reusable oss-checks workflow + dependabot/license templates #1 verification is pending the cx43 acceptance run on #390 reaching native-image compile without OOM.
2. The docs/hetzner-runners.md changes are on branch claude/suspicious-chatelet-f7637e and need a PR to land on main.
3. Optional: request the Hetzner limit increase if 16-vCPU runners are wanted in future.

Closing as resolved — the SKU decision is made and documented.