"А давайте сделаем сервис на 100% доступным". Хороший пост рассказывающий чего вам это будет стоит. Авторы говорят о 10x increase in development costs(!)
Спойлер, определите уровень который нужен вам врядли это именно 100%, каждая 9 после 99% стоит оочень много.

"Say a feature is estimated to take 20 days of development (including design). Add a further 10 days for testing (using the top end industry estimate of one-third time), and you have a total of 30 days cost for the good reliability feature. For the 100% reliability feature, we need much more testing, around 200 days using Colm’s talk. That means a total of 30 days for adding a feature with good reliability becomes 220 days for 100% reliability. More than seven times the cost. These are just rough estimates, but conservative and indicative of how there is a 10x increase in development costs."

https://medium.com/expedia-group-tech/the-cost-of-100-reliability-ecb2901f23a4