docs: update deploy design for public-ingress pivot + publicOnlyTransport finding
Records that the in-cluster Service DNS could not be used for a dashboard-registered worker (engine publicOnlyTransport SSRF guard blocks internal addresses), the pivot to st-app chart + public ingress at arcade-eval-ref.st.dev (CNAME -> k8s-backstage.st.dev), and the verified end-to-end whoami result. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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# Deploy arcade-eval reference MCP server to backstage k8s
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**Date:** 2026-06-22
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**Status:** Approved — implementing
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**Status:** DONE — deployed and verified end-to-end.
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## Goal
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Replace the ephemeral cloudflared **quick tunnel** (used to register the
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`arcade-eval-ref` server with the self-hosted Arcade engine) with a permanent
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in-cluster deployment on `backstage-wus2-v4`. The engine then reaches the server
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over stable cluster DNS instead of a `trycloudflare.com` URL that dies on restart.
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deployment on `backstage-wus2-v4`, so the engine reaches the server over a stable
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URL instead of a `trycloudflare.com` URL that dies on restart.
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Relevant eval categories: cat-4 (custom server dev), cat-8 (deployment), cat-9 (DX).
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## Architecture / data flow
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## Key finding that shaped the final design
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The first attempt registered the in-cluster **Service DNS**
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(`http://arcade-eval-ref.arcade-eval-ref.svc.cluster.local:8000`) as a dashboard
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worker. Health went green but **0 tools loaded**. Engine logs showed:
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```
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Arcade engine (ns: arcade) ──HTTP /worker/*──▶ Service arcade-eval-ref (ns: arcade-eval-ref)
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registered as type "Arcade" └─▶ Deployment: python:3.12 running
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URI = http://arcade-eval-ref.arcade-eval-ref mcp_server.server over HTTP :8000
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.svc.cluster.local:8000 (echo / add / whoami)
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Secret = ARCADE_WORKER_SECRET ◀── same value ──▶ env ARCADE_WORKER_SECRET (SealedSecret)
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Failed to get worker tools: Get ".../worker/tools":
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dial tcp 10.0.192.27:8000: publicOnlyTransport: blocked connection to internal address
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```
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**The Arcade engine has an SSRF guard (`publicOnlyTransport`) that blocks
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dashboard-registered worker URIs resolving to internal/private (RFC1918) addresses.**
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Only workers declared in the **engine config file** (e.g. the bundled `arcade-worker-main`
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at `http://arcade-worker-main:8001`) may use internal URIs. Health checks aren't guarded
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(hence green), but the authenticated `/worker/tools` discovery is. The cloudflared tunnel
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worked only because it was a *public* URL.
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⇒ A dashboard-registered in-cluster worker **must be exposed on a public URL**. (The
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worker secret was a red herring — the connection is refused before auth.)
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## Architecture / data flow (final)
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```
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Claude Code ──▶ gateway zeb-gateway-test ──▶ Arcade engine ──HTTPS /worker/*──▶
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https://arcade-eval-ref.st.dev (Cloudflare CNAME → k8s-backstage.st.dev → nginx ingress)
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└─▶ Service → Deployment: python:3.12 running mcp_server.server over HTTP :8000
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(echo / add / whoami). /mcp also served; /worker/* auth = ARCADE_WORKER_SECRET.
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```
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### Runtime facts (verified by introspecting `arcade-mcp-server` 1.17)
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- `app.run()` honors env overrides via `_get_configuration_overrides()`:
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`ARCADE_SERVER_TRANSPORT=http`, `ARCADE_SERVER_HOST=0.0.0.0`, `ARCADE_SERVER_PORT=8000`.
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So the hardcoded `127.0.0.1` in `server.py`'s `__main__` is overridden at runtime —
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**no `server.py` change needed.**
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- `ARCADE_WORKER_SECRET` (settings alias `arcade.server_secret`) → worker routes mount at
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`/worker/*` (what the engine calls); MCP also served at `/mcp`. FastAPI app, port 8000.
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`ARCADE_SERVER_TRANSPORT=http`, `ARCADE_SERVER_HOST=0.0.0.0`, `ARCADE_SERVER_PORT=8000`
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— so the hardcoded `127.0.0.1` in `server.py` is overridden at runtime (no code change).
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- `ARCADE_WORKER_SECRET` enables worker routes at `/worker/*`; the engine authenticates with
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an HS256 JWT (`aud=worker`, `ver=1`) signed with that secret. MCP is served at `/mcp`.
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## Components
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## Components (three repos)
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### 1. `arcade-eval` repo (branch off `main`)
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### 1. `arcade-eval` — image
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- `lib/mcp_server/Dockerfile` — `python:3.12-slim`, `pip install .`, HTTP transport via env,
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non-root, port 8000.
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- `.github/workflows/build-push-acr.yml` — pushes
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`servicetitandev.azurecr.io/arcade-eval-ref:1.0.<run_number>` (secrets
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`ACR_DEV_USERNAME`/`ACR_DEV_PASSWORD`). Adapted from `servicetitan/mem0`.
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- **`lib/mcp_server/Dockerfile`** — `python:3.12-slim`, `pip install .` (pulls
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`arcade-mcp-server` + `httpx`), `ENV` transport/host/port, non-root user, `EXPOSE 8000`,
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`CMD ["python","-m","mcp_server.server"]`.
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- **`.github/workflows/build-push-acr.yml`** — adapted from `servicetitan/mem0`. Pushes
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`servicetitandev.azurecr.io/arcade-eval-ref:1.0.<run_number>`. Login via repo secrets
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`ACR_DEV_USERNAME` / `ACR_DEV_PASSWORD`. Triggers: `workflow_dispatch` + push to `main`
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filtered to `lib/mcp_server/**`.
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### 2. `k8s-backstage-v2` — `apps/mcp/arcade-eval-ref/`
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- `namespace.yaml` — ns `arcade-eval-ref`.
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- `server.yaml` — **st-app HelmRelease** (chart 2.0.72): `image` pinned to `1.0.1`,
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`service.internalPort: 8000`, **`ingress.enabled` host `arcade-eval-ref.st.dev`
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class `nginx`, `oAuth.enabled: false`** (no SSO wall over `/worker/*` or `/mcp`),
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worker secret via `envFrom` from the SealedSecret, probes off. TLS = ingress default
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`*.st.dev` wildcard cert.
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- `sealedsecret.yaml` — `arcade-eval-ref-worker-secret` (key `ARCADE_WORKER_SECRET`),
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strict scope, sealed with the backstage-wus2-v4 sealed-secrets cert.
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### 2. `k8s-backstage-v2` repo (branch off `master`)
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### 3. `iac-terraform-workspaces` — DNS
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- CNAME `arcade-eval-ref.st.dev` → `k8s-backstage.st.dev` (st.dev zone), mirroring the
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`anvil`/`alerts` pattern.
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New dir **`apps/mcp/arcade-eval-ref/`** (Flux's `apps` Kustomization recursively applies
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everything under `apps/`; no per-dir `kustomization.yaml`):
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## Registration (dashboard)
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- **`namespace.yaml`** — ns `arcade-eval-ref` (labels per repo convention, `team: infra`).
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- **`server.yaml`** — plain `Deployment` (image
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`servicetitandev.azurecr.io/arcade-eval-ref:1.0.1`; no imagePullSecret — the cluster has
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native ACR pull, confirmed by other `apps/mcp/*` servers; `ARCADE_WORKER_SECRET` from
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secretRef; TCP probes; modest resources) + `Service` (ClusterIP, 8000→8000).
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- **`sealedsecret.yaml`** — `arcade-eval-ref-worker-secret`, key `ARCADE_WORKER_SECRET`,
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**strict** scope, sealed offline with `kubeseal --cert <backstage-wus2-v4 public cert>`.
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Add/repoint the worker: URI `https://arcade-eval-ref.st.dev`, Secret = the worker-secret
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plaintext (git-ignored at `results/arcade-eval-ref-worker-secret.txt`). The engine then
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fetches `/worker/tools` over the public URL → tools load → add to `zeb-gateway-test`.
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## Manual steps after merge
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## Verified
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1. Add `ACR_DEV_USERNAME` / `ACR_DEV_PASSWORD` repo secrets to `arcade-eval`.
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2. `workflow_dispatch` (or merge to `main`) to build/push the image — first run = tag `1.0.1`.
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3. Merge the k8s branch; Flux applies the namespace/secret/deployment.
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4. Dashboard → **Add Server → Arcade**, URI
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`http://arcade-eval-ref.arcade-eval-ref.svc.cluster.local:8000`, Secret = the worker secret
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plaintext (stored git-ignored at `results/arcade-eval-ref-worker-secret.txt`); re-point the
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`zeb-gateway-test` gateway's ref tools at it and drop the tunnel. Delete the plaintext file
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afterward.
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- `https://arcade-eval-ref.st.dev/worker/health` → 200 (valid `*.st.dev` LE cert);
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`/worker/tools` with a correct worker JWT → 200, tools `Echo/Add/Whoami`.
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- Through the gateway: `ArcadeEvalRef_Whoami()` → the caller's Entra `sub`
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(`GvgRofe5…`), proving per-user execution across the full
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client → gateway → engine → public URL → in-cluster pod chain.
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## Out of scope (YAGNI)
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## Alternative considered (not taken)
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No ingress (internal-only ClusterIP), no HPA, no PodMonitor/metrics (separate cat-5 work),
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single replica.
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Declare the server as a static worker in the **engine config** (`tools.directors[].workers`,
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like `arcade-worker-main`) — that path allows internal URIs and avoids public exposure, but
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edits the vendor Helm release (`apps/arcade`) and loses the dashboard per-project workflow.
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Public ingress was chosen as the lower-touch option.
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