Some things that every application or service you build should have:
- Logging (preferably centralized)
- Metrics (to know how the app is performing (slow endpoints, etc.))
- Alerts (to be notified when things aren't working properly)
- Telemetry (to know which parts of the app / service are used most, or not at all and can be removed)
- User Feedback Mechanism (so users can easily report issues or request new features)
- Feature Flags (to enable rolling features / changes out in a controlled manner)