Minimum Versions & Forced Upgrades

You need an escape hatch for critical bugs and unsustainable old versions. Expose an app config endpoint (or remote config) returning min_supported_version (hard block) and recommended_version (soft nag) per platform. Clients check it at launch and on 426 Upgrade Required-style errors. Use the platform features too: Android in-app updates (immediate/flexible) and App Store links on iOS. Hard upgrades are disruptive — reserve them for security issues or protocol breaks, and communicate.

Upgrade levers

{
  "ios":     {"min_supported_version": "5.4.0", "recommended_version": "5.12.0", "store_url": "https://apps.apple.com/app/id000000000"},
  "android": {"min_supported_version": "5.4.0", "recommended_version": "5.12.0"},
  "messages": {"upgrade_title": "Update required", "upgrade_body": "This version is no longer supported."},
  "ttl_seconds": 3600
}

MIN = {"ios": Version("5.4.0"), "android": Version("5.4.0")}

@app.middleware("http")
async def min_version_gate(request: Request, call_next):
    platform, version = parse_app_ua(request.headers.get("user-agent", ""))
    if platform in MIN and version and version < MIN[platform]:
        return problem(426, "upgrade-required", detail="Please update the app.")
    return await call_next(request)

Common pitfalls

• No upgrade mechanism in version 1.0 (you can never add it to old binaries).
• Hard-blocking for cosmetic changes.
• Blocking the config endpoint itself behind auth.

Key points

• Ship the upgrade check in v1
• Soft vs hard thresholds
• Prefer compat shims; hard block rarely

Further reading: Android: In-app updates