A web system that must process 1,800 requests per second at peak is being designed. One server can process at most 250 requests per second, and each server's utilization should be kept at 70% or less. In addition, the remaining servers must still meet this condition if one server fails (N+1 configuration). With the load spread evenly, which is the minimum number of servers required?

Answer: C. 12 servers

At 70% utilization or less, one server can process 250 × 0.7 = 175 requests per second, so the number needed at peak is 1,800 ÷ 175 ≈ 10.3, rounded up to 11. One more is added so that these 11 remain even if one server fails, giving 11 + 1 = 12 servers. 9 servers is 7.2 (1,800 ÷ 250, ignoring the utilization limit) rounded up to 8 plus one, and 11 servers does not consider failures.

• A. This ignores the utilization limit and adds one to 8 servers.
• B. This considers the utilization limit but lacks the spare server for a single failure.
• C. Correct. 1,800 ÷ 175 rounded up gives 11, plus one spare makes 12.