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A service that receives 12,000 requests per hour performs a canary release of a new version, sending only 5% of the requests to it. The new version has a bug that makes 3% of the requests it receives fail; it is noticed after one hour, and all requests are returned to the old version. Which of the following is the number of requests that failed because of the bug during that hour?

  1. A18
  2. B360
  3. C600
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Answer: A. 18

The new version received 12,000 × 5% = 600 requests, and 3% of them failed, so 600 × 3% = 18 requests failed. Had all requests been switched to the new version at once, 12,000 × 3% = 360 would have failed. A canary release limits the requests affected by a bug to a small share in this way and increases the share if there is no problem, while watching indicators such as error rate and response time. Comparing the indicators of the new and old versions needs enough requests, so the share and the observation time are decided together.

  • A. Correct. 12,000 × 0.05 × 0.03 = 18.
  • B. This is the number if all requests had been sent to the new version (12,000 × 0.03).
  • C. This is the number of requests sent to the new version (12,000 × 0.05); only 3% of them failed.
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