KCNA Cloud Native Architecture Practice Question
In a microservices application, you want to prevent cascading failures by limiting the number of concurrent requests to a downstream service. Which resilience pattern should you implement?
⚠ Common exam trap
KCNA often tests the confusion between bulkhead (limit concurrency/isolation) and circuit breaker (stop calls after failures); candidates pick circuit breaker because both address cascading failures, but only bulkhead limits concurrent requests.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Bulkhead pattern
The bulkhead pattern isolates resources by limiting the number of concurrent calls to a downstream service, so that a slow or failing dependency cannot exhaust the caller's thread pool or connection pool and cause cascading failures. In microservices, bulkheads partition thread pools, connection pools, or instances per dependency (e.g., Hystrix thread pool isolation), so one degraded service only saturates its own compartment. This directly matches the requirement of limiting concurrent requests to a downstream service.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Circuit breaker
Why it's wrong here
A circuit breaker stops calls once a failure threshold is crossed, protecting the caller from a dead dependency, but it does not cap the number of concurrent requests reaching a healthy-but-slow service. It suits fast-failing an unavailable dependency; concurrency limiting needs a bulkhead or semaphore.
- ✗
Timeout pattern
Why it's wrong here
A timeout caps how long a single call waits before failing, but it does not cap how many calls are in flight, so a slow downstream service still accumulates concurrent requests until it collapses. Timeouts suit detecting unresponsive calls; the pattern that limits concurrent requests is bulkhead or rate limiting.
- ✓
Bulkhead pattern
Why this is correct
The bulkhead pattern isolates resources into separate pools, so each downstream service receives a bounded number of concurrent requests. When one service saturates its pool, others continue unaffected, preventing the cascading failure the stem describes. Circuit breaking and retries address different failure modes.
- ✗
Retry pattern
Why it's wrong here
Retry re-sends failed requests, which multiplies load on an already-struggling downstream service and accelerates the cascade rather than preventing it. Retries suit transient, isolated faults such as a dropped packet; limiting concurrent requests requires bulkhead isolation or a concurrency limiter, not repeated attempts.
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Last reviewed September 2026 · checked against the official CNCF exam blueprint
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