Ketersediaan (sistem isih urip lan bisa diakses) lan keandalan (sistem berfungsi kanthi bener) iku syarat non-fungsional sing penting. Entuk maneh durung mbutuhake redundansi, toleransi kegagalan, ngilang titik kegagalan tunggal, lan nangani kegagalan kanthi apik.
Ketersediaan vs keandalan
AVAILABILITY → the system is UP and responsive (accessible when needed):
→ measured as uptime % ("nines": 99.9% = ~8.7h/year down; 99.99% = ~52min/year)
RELIABILITY → the system works CORRECTLY (does what it should, without failures/errors):
→ related but distinct (a system can be up but returning wrong results — available but
unreliable)
→ both matter: users need the system available AND working correctly.
