How Can EC2 Instances Share CMS Content with Least Lag?
Short answer
B Mount a shared Amazon EFS file system on every EC2 instance so all CMS website assets stay consistent with minimal lag.
Question
Key Takeaways
The test is shared storage for a multi-AZ EC2 CMS; the trap is choosing Amazon S3 with scheduled sync or EBS snapshots that create stale, per-instance copies.
This SAA-C03 question asks how to keep website assets synchronized across EC2 instances in an Auto Scaling group with the least possible lag. The correct answer is Amazon EFS (B), because every instance mounts the same shared file system instead of relying on delayed copies or per-instance storage.
Common mistake: Candidates often choose S3 with hourly sync (C) because S3 is durable and scalable, but the sync interval adds up to an hour of lag and each EC2 instance keeps a separate EBS copy, violating the least-lag requirement.
Expert Analysis
Why the Answer Is Correct
Amazon EFS is a regional, POSIX-compliant shared file system that multiple EC2 instances across Availability Zones can mount at the same time. In this CMS scenario, users add and update files continuously, so the website assets must live in one shared location rather than in per-instance storage. When each EC2 instance mounts the same EFS file system and the CMS references assets there, a write by one instance is immediately visible to the others, satisfying the "least possible lag time" requirement. EFS also scales storage and throughput elastically as the Auto Scaling group adds instances, which fits the multi-AZ architecture. This is why option B is the correct SAA-C03 answer.
Why the Other Options Are Wrong
Option A tries to copy assets from the newest EC2 instance through user data and then restrict ALB updates to that instance, but user data runs only at launch and the ALB cannot reliably route content changes to one specific instance; other instances would serve stale assets. Option C uses Amazon S3 as the source and an hourly S3 sync into each instance's EBS volume, which creates up to an hour of lag and leaves each instance with its own divergent copy. Option D restores a point-in-time EBS snapshot as a secondary volume, but EBS volumes are tied to a single Availability Zone and snapshots are static, so new writes are not shared across the fleet. None of these alternatives provides a single, always-current shared content store.
Community Comment Notes
Scheldon noted that B "Looks like this is the only reasonable solution from all presented," reflecting the consensus that the other options fail the shared-content requirement. mk168898 emphasized that "website content must be in sync with all EC2 instances, so use EFS," which matches the core design principle tested here. sandordini added that a "CMS is usually EFS," a useful shortcut for recognizing shared file storage scenarios on SAA-C03. ike001 also selected B, and the anonymous vote record is unanimous for B, though the technical reasoning above is what ultimately supports the verdict.
Official Reference
These links open the official vendor documentation in a new tab.
Exam Strategy
When a question says multiple EC2 instances must share the same up-to-date files with minimal lag, eliminate any option that copies data to per-instance EBS or relies on scheduled S3 syncs. The AWS-native shared file system for Linux EC2 is Amazon EFS, so look for a mountable, multi-AZ file system as the answer.
Frequently Asked Questions
Why is an hourly S3 sync to EBS not the best fit for shared CMS assets?
Why can't a secondary EBS volume from a snapshot share content across AZs?
Community Votes
100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 4 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 4
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Scheldon 👍 2 Answered BAnswerB Looks like this is the only reasonable solution from all presented
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mk168898 👍 1 Answered Bwebsite content must be in sync with all EC2 instances, so use EFS
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sandordini 👍 4 Answered BCMS is usually EFS
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ike001 👍 1B is the answer
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