convex-migrate-rehearse

par get-convex

Répéter un changement de schéma d'application en direct et un backfill sur un déploiement d'aperçu amorcé par snapshot, vérifier, puis promouvoir le changement éprouvé en production avec le snapshot comme restauration.

npx skills add https://github.com/get-convex/agent-skills --skill convex-migrate-rehearse

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Rehearse a schema change on a preview before prod

A schema push on Convex validates every existing document against the new schema and FAILS the push if any row doesn't conform — a real data-conformance gate. The safe way to use that gate is to let it fail on a rehearsal copy, not on prod. This capability turns a preview deployment into that copy: seed it with a prod snapshot, push the new schema + run the backfill there, watch the gate, and only promote once it's green. It composes deploy-guard (target classification), migrate (the optional-then-tighten pattern), and @convex-dev/migrations (the batched, resumable backfill).

Workflow

PRECONDITION: preview deployments need a Preview Deploy Key (dashboard → Project Settings → Deploy Keys → Preview) exported as CONVEX_DEPLOY_KEY before any --preview-create/--preview-name deploy — a plain npx convex login session cannot create previews, and this is a paid-tier feature. If no preview key is available, fall back to rehearsing on the personal dev deployment seeded with the snapshot, and say so.
GUARD: deploy-guard — classify + announce the SOURCE (prod, being read) and the eventual TARGET (prod, being changed); get the fresh explicit yes for the prod promote up front and confirm the plan.
SNAPSHOT the source data read-only: npx convex export --path snapshot.zip (from the deployment holding the real data; add --include-file-storage only if the migration touches files). This is a read; it changes nothing.
CREATE the preview FROM THE PRE-CHANGE CODE — do this BEFORE editing schema.ts, so the preview starts on the schema the snapshot data already conforms to: npx convex deploy --preview-create migrate-<slug> (needs the preview key; auto-expires ~5 days). Seed it: npx convex import snapshot.zip --deployment migrate-<slug> (import targets a deployment by NAME with --deployment; there is no --preview-name flag on import). The import succeeds because the data still matches the old schema.
REHEARSE on the preview, in the migrate order — each push is npx convex deploy --preview-name migrate-<slug> (re-deploys to the SAME preview, keeping its data; NOT convex dev, which targets personal dev): (a) make the new/changed field OPTIONAL and deploy — if existing rows violate it the push FAILS HERE on the copy with the offending shape; fix and re-push until green. (b) write a @convex-dev/migrations backfill and run it against the preview; verify every row is now valid. (c) tighten the validator (required / narrowed union) and deploy again — the gate now passes because the backfill ran.
VERIFY on the preview: run the app's functions against the migrated data (MCP run/runOneoffQuery pointed at the preview, or a smoke query) to confirm behavior and shape.
PROMOTE only on the fresh explicit yes from step 1: apply the SAME sequence to prod (optional schema → backfill → tighten). Because it already succeeded on prod-shaped data, the prod push repeats a proven run. Keep the snapshot as the rollback artifact (npx convex import snapshot.zip --replace --prod); state plainly that data written after the snapshot is lost, so keep the promote window short.
CLEAN UP: the preview auto-expires; delete the local snapshot when done (it holds real data — treat it as sensitive, never commit it).

Rules

Create the preview from the PRE-CHANGE code and seed the snapshot BEFORE editing schema.ts — so the import conforms and the conformance gate then fails on the copy (not prod) when you push the change; each preview push is deploy --preview-name, import targets it with --deployment.
Follow the migrate order every time: optional field → push → backfill → verify → tighten → push; skipping 'optional first' makes the very first push reject existing rows.
The prod promote needs a fresh explicit yes (deploy-guard) and is a REPEAT of the proven preview run, not a new attempt.
Keep the prod snapshot as the rollback artifact; state plainly that a snapshot-restore loses data written after the snapshot, so keep the promote window short.
Treat the exported snapshot as sensitive real data: delete it locally when finished; never commit it.
Backfills go through @convex-dev/migrations (batched, resumable, dry-runnable), not ad-hoc one-shot mutations over a whole table.
This is the rehearsal-and-promote flow; for the plain 'explain optional-then-tighten' guidance with no live data, that's migrate.