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Français · Type: explanation + how-to · Audience: admin · Context: hosted Studio · Status: ready · Applies from: 4.2.3

The Studio Server (hosted team Studio) · contract: experimental · verified by CI (support matrix of 4.4.0, 2026-10-23): Postgres, S3 and Keycloak in CI; Chromium and Firefox (job studio-hosted); WebKit on macOS, by hand only · automated checks: jobs studio-hosted, studio-install-smoke; CI plan studioHosted; 3 test files · people's passes: studio-hosted not run (#149), studio-collab not run (#150), studio-preview not run (#166), studio-assets-hosted not run (#167), studio-mcp-remote not run (#196), studio-oidc-generic not run (#197) · known limits: client-retry

On Clever Cloud a deploy (or a push, or clever restart) starts the new instance while the old one still serves. The Studio Server is built for that overlap: no write is lost, but writes are slow or refused for about a minute. This page says why, what was measured, and how to deploy so that members are not surprised.

Why

Spike S measured it on 17 October 2026: during clever restart --without-cache, the new instance started while the old one still answered, and the old one never logged a SIGTERM. Two instances writing the same game at once would corrupt its history, and waiting for a signal that does not come would stall the switch. So:

• The instances share a service lease in PostgreSQL: one holds it and serves writes. It lasts 30 s and is renewed every 10 s on the database's clock; an instance that cannot renew stops writing by its own clock before the 30 s can pass.
• The new instance starts, answers /startz (Clever's health check, CC_HEALTH_CHECK_PATH=/startz), then waits: /readyz is 503 ("writes":"waiting") and its writes are 503 with Retry-After: 2 ("this instance does not serve writes yet; try again").
• The handoff (since 4.2.3). Once it listens, the new instance asks for the lease; the holder gives it back at its next renewal (10 s at most) and logs {"event":"lease-lost",…}; the new one logs {"event":"lease-taken",…}. An older instance never takes the lease back from a newer one.
• A client retries a refused write with the same operation id (X-Studio-Op) and it is applied once. The journal's own fenced lease still keeps two instances from writing over the same head.

What was measured

Clever Cloud keeps the old instance STOPPING for about two minutes, still receiving requests until the deploy ends, and it logs no stopping line.

Measure · handoff-window Between two versions that both hand the lease over (two clever restart of the same commit): lease-taken 6.0 s and 10.1 s after the new instance listened; then writes were 503 (Retry-After: 2) for 16 s and 10 s, because Clever still sent requests to the old instance, which no longer held the lease, until the deploy ended. Before that, while the new instance started, one write waited 10.2 s and 19.4 s on its journal check and got a 503 too, then went through on a retry. No 409, no 500, no write applied twice.

• date: 2026-10-19
• version: 4.2.2
• volume: two redeploys, a probe reading /readyz every second and writing a note every 3 s
• conditions: reference deployment, studio app XS, one instance, PostgreSQL DEV, region par; engine at commit dd66b38d on main before the 4.2.3 tag (package.json said 4.2.2); one sample per deploy
• source: QUALIF-4.2.3-REFERENCE.md §5 bis

In all, about a minute of slow or refused writes per deploy, none lost.

Measure · first-deploy-onto-handoff The first deploy onto a version with the handoff, from one without it (4.2.2, or a 4.2.3 commit before #183): the old version kept the lease until Clever stopped it, and writes were refused for 2 min 23 s and 2 min 27 s, reads going on.

• date: 2026-10-19
• version: 4.2.2
• volume: two deploys (52e68932 → c66fbf56, then c66fbf56 → dd66b38d), the same probe
• conditions: reference deployment, studio app XS, PostgreSQL DEV, region par; engine commits on main before the 4.2.3 tag (package.json said 4.2.2)
• source: QUALIF-4.2.3-REFERENCE.md §5 and §5 bis

While both instances run they hold twice the connections: on the PostgreSQL DEV plan (5) background work fails with "too many connections" during each deploy, and an older version's write could fail with it (a 500). Take a larger plan for a deployment people use (Apps and add-ons).

Deploying without surprising the team

Verified on: 19 October 2026 (the measures above; engine commits before the 4.2.3 tag, package.json 4.2.2). This page's text itself is not verified on a live installation.

1. Tell the members, or pick a quiet moment: about a minute of slow writes; about two and a half minutes of refused writes for the first deploy onto 4.2.3 or later from an older version.

2. Deploy from your machine, in the engine repository, the worker first when both change:

   # on your machine, in the engine repository
   clever deploy --alias my-game-worker
   clever deploy --alias my-game-studio

3. Watch /readyz come back to 200 and the lease-taken line (its instance is the new one):

   # on your machine
   until curl -sf https://studio.example.fr/readyz; do sleep 2; done

4. Make one write (a note) and see it saved, at the next revision.

Limit · client-retry "None lost" holds for a client that retries a 503 with the same operation id. The Studio in the browser does, up to 8 tries with waits growing to 8 s (about 40 s in all), so a window longer than that (the first deploy onto the handoff) ends in a refusal it shows. The local MCP's tools pointed at a hosted Studio send an operation id but do not retry: they report the 503, and the tool is run again. A script of your own that does not retry loses the write it sent during the window.

Alternatives set aside

• Relying on SIGTERM to hand the lease over: Clever never delivered it observably (spike S, the reference deployment).
• Stopping the old instance first (clever stop, then deploy): a minute or more with no Studio at all. Kept for one case only, a migration that changes what the old version reads (Upgrading the server).
• Several instances serving at once: the journal needs one writer per game.

Trade-offs

The handoff shortens the refused window from minutes to seconds, but Clever's routing to the old instance until the deploy ends keeps 10 to 16 s of 503. A /readyz alert must tolerate that (Monitoring).

Decisions and ADRs

• The lease: studio-server/src/server/service-lease.ts (master plan §4, P8); ADR 0025.
• The measures: docs/dev/SPIKE-4.2.1-CLEVER.md §2, docs/dev/QUALIF-4.2.3-REFERENCE.md §5 and §5 bis.
• A 503 seen by a member: Troubleshooting.

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