Practice
1. In a system trace, at step 4 the circuit breaker checks the failure count before forwarding a request. What happens if the failure count exceeds the threshold at this step?
easy
Solution
Step 1: Trace circuit breaker decision at Step 4
When failure count exceeds threshold, the circuit breaker transitions to OPEN state and stops forwarding requests.Step 2: Understand behavior on open circuit
Requests are immediately failed (B), not forwarded (A), retried (C), or queued (D).Final Answer:
Option A -> Option AQuick Check:
Open circuit returns error immediately without downstream call [check]
Hint: Open circuit returns error immediately, no downstream call [OK]
Common Mistakes:
2. In a sliding window rate limiter, at step 3 the system records a new request timestamp. What happens internally to the stored counters at this step?
easy
Solution
Step 1: Understand sliding window counter mechanics
Sliding window counters maintain timestamps of recent requests and remove those outside the window to keep an accurate count.Step 2: At step 3, old timestamps beyond the window are purged before adding the new request timestamp
This ensures the count reflects only requests within the sliding window duration.Final Answer:
Option A -> Option AQuick Check:
Sliding window removes expired timestamps before counting new requests [check]
Hint: Sliding window purges old timestamps before counting new ones [check]
Common Mistakes:
3. In a system where a user requests access to a protected resource, at step 4 the Authorization Service checks the user's access token. What happens if the token is expired at this step?
easy
Solution
Step 1: Understand Authorization Service behavior at token validation
The service validates token expiry and rejects expired tokens.Step 2: Eliminate incorrect behaviors
Granting access with expired token violates security; automatic refresh is done by Authentication Service, not Authorization; forwarding without validation breaks security.Final Answer:
Option D -> Option DQuick Check:
Expired tokens cause 401 Unauthorized rejection [check]
Hint: Expired token -> Authorization rejects with 401 Unauthorized [check]
Common Mistakes:
4. For a system tracking SLO error budgets with high write volume and low latency requirements, which architecture is best suited to ensure accurate, near real-time error budget updates?
medium
Solution
Step 1: Analyze latency and accuracy requirements
Near real-time updates require continuous stream processing rather than batch or polling.Step 2: Evaluate each architecture against these requirements
Batch processing (A) and hourly rollups (D) are too slow; polling (C) introduces latency and load spikes; stream processing (B) provides continuous, low-latency computation.Final Answer:
Option C -> Option CQuick Check:
Stream processing -> continuous, low-latency error budget updates [check]
Hint: Stream processing fits low latency and high write volume best [OK]
Common Mistakes:
5. At 10x traffic scale, which component in a system using a Reverse Proxy, API Gateway, and Load Balancer is most likely to become the bottleneck first, and why?
hard
Solution
Step 1: Analyze component scaling characteristics
Load Balancers typically handle stateless TCP connections and can be scaled horizontally; Reverse Proxies cache but can be scaled with eviction policies; DNS load balancing is not a runtime bottleneck.Step 2: Identify CPU-intensive bottleneck
API Gateway performs authentication, rate limiting, and transformations per request, which are CPU and memory intensive and harder to scale linearly.Final Answer:
Option A -> Option AQuick Check:
API Gateway CPU load scales with request complexity, causing bottleneck [check]
Hint: API Gateway CPU-heavy tasks cause first bottleneck at scale [check]
Common Mistakes: