Question 1377

Shedding Looks Like Success

This function defines the availability SLI for an API. During the evening peak the service starts shedding load and returns 429 Too Many Requests to about 8 percent of traffic, but the SLO dashboard stays at 99.98 percent while support tickets pile up.

def is_good(req):
    return req.status < 500

sli = sum(is_good(r) for r in requests) / len(requests)

What is the right correction?

A

Switch from a request-ratio SLI to time-based availability, measuring the minutes in which the service was up

B

Count 429 as a failure while leaving 4xx caused by malformed client requests as successes, since a 429 is your service declining to serve a well-formed request

C

Count every 4xx as a failure, because users experience all of them as the service not working

D

Leave the SLI alone and put the 429 rate on its own dashboard with a separate alert