ADR-0019: Official Demo runtime — Railway-only (real MySQL 8)

• Status: Accepted (2026-08-02)
• Decision makers: Project maintainers

Context

ADR-0018 set: docs / static demo via Cloudflare Pages, images via GHCR, no production VPS; public demo API deferred separate step. Static site DEMO_API_URL may be empty; full trial needs public backend + MySQL + Redis.

Previously evaluated "TiDB Serverless + Upstash Redis + some container host" three-vendor assembly, and domestic PaaS (Zeabur) vs Railway plugin-in-one. Maintainer registered Railway and Zeabur; prior decision: official demo default = Railway-only.

Decision

Role	Host	Notes
Official demo backend	Railway (single project)	App service runs ghcr.io/erdonline/erdonline-backend (or Dockerfile); MySQL plugin (MySQL 8) + Redis plugin; env vars align Spring Boot (DB_* / REDIS_* / JWT_*, etc.)
Static demo frontend	Cloudflare Pages (ADR-0018)	Variable DEMO_API_URL → Railway public HTTPS root URL
China region fallback	Zeabur	Same idea (container + managed MySQL/Redis); not official default path, docs brief mention only
User production / self-host	docker compose (ADR-0018)	Project does not host user production data; compose + GHCR still recommended production path

Explicitly rejected:

• TiDB + Upstash (or other) three-vendor assembly as official demo: multiple bills, multiple failure surfaces, dialect/compatibility mental load, not worth demo scale
• Treating Railway/Zeabur demo as "official production" or self-host replacement
• Long-term VPS purchase for demo (does not overturn ADR-0018)

Consequences

• Positive: one Dashboard App + real MySQL 8 + Redis; same data plane shape as compose (dual DB martin/erd); cost controllable (Hobby ~$5–10/month order of magnitude, per Railway billing)
• Cost: need release tag before GHCR has pullable image; empty DB must manual/mysql load db/init (Flyway only covers erd incremental); cross-origin needs ERD_UI_URL; SocketIO :9092 may be unavailable on single HTTP port platform (demo REST-first)
• Dashboard hard settings (cannot write to toml): App Root Directory = backend; Config as Code = /backend/railway.toml. Otherwise monorepo root build fails; before first v* do not use GHCR Image that doesn't exist yet
• vs existing ADR: fills ADR-0018 "public demo API" gap; does not change self-host compose source of truth
• Ops steps: see Deployment — Railway official demo; China fallback see Zeabur