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Question 38

A new upstream API is being designed to offer an SLA of 500 ms median and 800 ms maximum (99th percentile) response time. The corresponding API implementation needs to sequentially invoke 3 downstream APIs of very similar complexity.

The first of these downstream APIs offers the following SLA for its response time: median: 100 ms, 80th percentile: 500 ms, 95th percentile: 1000 ms.

If possible, how can a timeout be set in the upstream API for the invocation of the first downstream API to meet the new upstream API's desired SLA?

    Correct Answer: C

    The upstream API's desired SLA is 500 ms median and 800 ms 99th percentile response time. The first downstream API has a median response time of 100 ms and a 95th percentile response time of 1000 ms, which means in 5% of cases, it can take up to 1000 ms. With such variability, it is impossible to guarantee meeting the stringent SLA of the upstream API even if a timeout is set. Therefore, either a different SLA must be negotiated with the first downstream API or an alternative API must be invoked.

Discussion
FreedoxOption: C

I think it's C. In the case of the first one finishing at 500ms, upstream will time out without even completing the 2nd and 3rd calls.

calazansOption: B

Set a timeout of 100 ms; that leaves 400 ms for the other two downstream APIs to complete

AB317Option: B

Answer: B