<aside> ⚙ No. of people = $10^{10}$ No. of images uploaded per user per month = 2 (average) Images cached per session, per user (window size) = 5 Avg. image size = $5 \times 10^6$ bytes Avg. server cost = $0.01/GB (similar to AWS S3) Avg. redis cache cost = $0.03/GB (basis: volatile mem: ssd = 3:1)

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$$ \begin{align*} \text{Total storage cost} &=\frac {10^{10} \times 2 \times 5 \times 10^6 \times 0.01} {10^9} \\ &= \bold{\$1M/month} \end{align*} $$

$$ \begin{align*} \text{Total volatile mem cost} &=\frac {10^{10} \times 5 \times 5 \times 0.02 \times 10^6} {10^9} \\ &= \bold{\$5M/month} \end{align*} $$

$$ \bold {Total\ server\ cost \approx \$200k/day} $$