Practice
1. In a distributed counter system using sharded CRDTs, at Step 4 the Aggregator node merges shard states received from replicas. What is the Aggregator's state immediately after merging two shards with counts 100 and 150?
easy
Solution
Step 1: Understand CRDT merge semantics for counters
Sharded counters merge by summing counts from each shard to reflect total increments without double counting.Step 2: Apply merge to counts 100 and 150
Sum is 250, representing combined increments from both shards.Final Answer:
Option C -> Option CQuick Check:
CRDT counters merge by summing shard values [check]
Hint: CRDT counters merge by summing shard counts [check]
Common Mistakes:
2. A web crawler must efficiently avoid re-crawling the same URLs too frequently while ensuring freshness. Which component best handles URL scheduling and politeness constraints?
easy
Solution
Step 1: Identify URL scheduling role
The URL Frontier manages which URLs to crawl next, enforcing politeness and freshness constraints.Step 2: Evaluate other components
PageRank ranks pages post-crawl, not for scheduling. Distributed KV stores hold content but don't schedule. Random distribution ignores politeness.Final Answer:
Option A -> Option AQuick Check:
URL Frontier enforces crawl politeness and freshness [check]
Hint: URL Frontier schedules URLs with politeness [check]
Common Mistakes:
3. A load balancer must detect unhealthy backend servers and reroute traffic without client impact. Which component is primarily responsible for detecting server health status?
easy
Solution
Step 1: Identify health detection responsibility
The health check module actively probes backend servers to determine their health status.Step 2: Eliminate other options
DNS resolver changes are slow and indirect; session persistence caches track sessions, not health; client-side retries do not detect server health.Final Answer:
Option A -> Option AQuick Check:
Health check module probes servers directly for health [check]
Hint: Health checks probe servers directly to detect failures [check]
Common Mistakes:
4. Without the Global Traffic Manager component in a multi-CDN setup, what is the most likely failure scenario when one CDN provider becomes unavailable?
medium
Solution
Step 1: Understand role of Global Traffic Manager in failover
It dynamically routes traffic away from failed CDNs. Without it, failover must be handled elsewhere.Step 2: Trace failure without Global Traffic Manager
Origin server may attempt to redirect traffic, but this adds latency and is less dynamic than traffic manager.Step 3: Eliminate other options
Automatic client failover (A) requires client intelligence not assumed here. Clients sending to failed CDN (B) is possible but less likely if origin redirects. Edge caches (D) do not replicate across CDNs automatically.Final Answer:
Option A -> Option AQuick Check:
Without traffic manager, origin server redirects traffic causing latency and partial failover [check]
Hint: No traffic manager -> origin server handles failover with latency penalty [OK]
Common Mistakes:
5. At 10x scale, which component in the CI/CD pipeline is most likely to become the bottleneck first, and why?
hard
Solution
Step 1: Analyze artifact registry scaling challenges
At 10x scale, artifact volume grows massively, increasing storage needs and retrieval latency, stressing the registry's throughput and storage backend.Step 2: Compare other components
Test runner scales with parallelism; orchestrator is stateless or sharded; rollback manager writes are less frequent and can be batched.Final Answer:
Option A -> Option AQuick Check:
Artifact registry storage and latency bottleneck at scale [check]
Hint: Artifact registry storage grows fastest, bottleneck first [check]
Common Mistakes: