ANS-C01 Network Design Practice Question
A company is designing a network architecture for a critical application that requires sub-millisecond latency between EC2 instances in the same placement group. The instances will be launched in a single Availability Zone in us-east-1. Which combination of features should be used to achieve the lowest latency?
⚠ Common exam trap
A common mix-up: candidates assume Enhanced Networking (ENA) is the best option for low latency because it is widely used for high-throughput workloads, but they overlook that EFA's OS-bypass is specifically designed for sub-millisecond latency in tightly coupled HPC applications.
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
✓
Launch instances in a cluster placement group with Elastic Fabric Adapter (EFA) enabled.
Elastic Fabric Adapter (EFA) provides OS-bypass capabilities that enable HPC and machine learning workloads to achieve sub-millisecond latency by bypassing the operating system kernel for inter-instance communication. Combined with a cluster placement group, which ensures instances are in close physical proximity within a single Availability Zone, this configuration delivers the lowest possible latency for tightly coupled applications.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Launch instances in a cluster placement group with Enhanced Networking (ENA) enabled.
Why it's wrong here
Cluster placement group provides low latency, but ENA is standard; EFA provides even lower latency.
- ✗
Launch instances in a spread placement group with SR-IOV enabled.
Why it's wrong here
SR-IOV is not a separate feature; it's similar to ENA. Spread placement group increases latency.
- ✗
Launch instances in a spread placement group with Enhanced Networking (ENA) enabled.
Why it's wrong here
Spread placement group spreads instances to reduce risk of simultaneous failure, but increases latency.
- ✓
Launch instances in a cluster placement group with Elastic Fabric Adapter (EFA) enabled.
Why this is correct
Cluster placement group minimizes network distance, and EFA provides OS-bypass for low latency.
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