What is the difference between EC2 instance store and EBS?
Interviewer Expectations for this Question
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Core Competency
Assesses fundamental understanding of AWS conventions, runtime behavior, and memory/performance considerations.
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Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
Both provide block storage to EC2, but with different durability and lifecycle.
- Instance store is physically attached NVMe or SSD storage on the host. It offers very high IOPS and low latency, but data is ephemeral: it is lost on stop, terminate, or host failure. It cannot be detached or snapshotted.
- EBS is network-attached, replicated within an Availability Zone, and persists independently of the instance. Volumes can be detached, reattached, and snapshotted to S3. It supports encryption, resizing, and volume types tuned for IOPS (io2), throughput (gp3), or cold data (sc1).
Choose instance store for caches, scratch space, and temporary buffers. Choose EBS for boot volumes, databases, and anything that must survive a reboot. Many workloads combine them: instance store for a cache layer and EBS for durable data.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.