350-901 Question #68: Real Exam Question with Answer & Explanation

Question

The script uses the Cisco Intersight REST API. Drag and drop the code snippets from the left onto the item numbers on the right to match the missing sections in the Python script to update the firmware on specific Cisco Intersight USC rack server.DMZ_R3-ADJM. Not all code snippets are used.

Explanation

This question assesses the test-taker's ability to complete a Python script that implements a robust API retry mechanism using exponential backoff and a maximum retry limit, specifically handling HTTP 429 status codes.

Approach. The correct interaction is to drag the appropriate code snippets to their corresponding numbered items based on standard retry logic and Python syntax:

• Drag '429' to <item 1>: Inside the except block, the if (response.status_code != <item 1>) condition checks if the error status code is not a specifically retriable one (like 429 'Too Many Requests'). If it's a different, likely non-transient error (e.g., 400, 401, 404, 500), or if the retry limit is hit, the script should return. By checking response.status_code != 429, we ensure that if a 429 error occurs and the retry limit isn't met, the script proceeds to sleep and retry, which is the intended behavior for transient 'Too Many Requests' errors.
• Drag 'RETRIES' to <item 2>: The condition i >= <item 2> determines if the maximum number of retries has been exhausted. RETRIES is initialized to 6, serving as the upper limit for the retry counter i.
• Drag 'backoff' to <item 3>: The time.sleep(<item 3>) function pauses the script for a duration specified by the backoff variable. This implements the wait time before the next retry attempt.
• Drag 'backoff' to <item 4>: The line <item 4> *= 2 is responsible for doubling the backoff duration, implementing the exponential backoff strategy for subsequent retries.
• Drag 'i' to <item 5>: The line <item 5> += 1 increments the retry counter i after each failed attempt, moving towards the RETRIES limit.

Common mistakes.

• common_mistake. Common mistakes include incorrectly assigning the variables:
• Using 'i' or 'RETRIES' for <item 3> or <item 4>: 'i' is the retry count, not a sleep duration, and 'RETRIES' is a constant for the maximum attempts, not a dynamic sleep variable. This would break the exponential backoff or the sleep mechanism.
• Using '429' for <item 2>: '429' is an HTTP status code, not a retry limit. Comparing the retry count 'i' against '429' makes no logical sense in this context.
• Swapping 'i' and 'backoff' for <item 4> and <item 5>: This would incorrectly increment the backoff variable and exponentially multiply the retry counter, leading to a dysfunctional retry mechanism.

Concept tested. API error handling, retry mechanisms, exponential backoff, HTTP status codes (specifically 429 Too Many Requests, which indicates rate limiting and often warrants retries), Python's try-except blocks, while True loops, and basic variable manipulation.

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