Shared Storage for Multi-AZ Web App with Strong Consistency

SAA-C03 By islever Editorial Last updated

Determine high-performing and/or scalable storage solutions. Determine high-performing and/or scalable network architectures.

Short answer

BE Use Amazon EFS for shared file storage across AZs and Amazon S3 with CloudFront for strongly consistent object delivery with cache control.

Question

A solutions architect is designing a shared storage solution for a web application that is deployed across multiple Availability Zones. The web application runs on Amazon EC2 instances that are in an Auto Scaling group. The company plans to make frequent changes to the content. The solution must have strong consistency in returning the new content as soon as the changes occur. Which solutions meet these requirements? (Choose two.)
  1. Use AWS Storage Gateway Volume Gateway Internet Small Computer Systems Interface (iSCSI) block storage that is mounted to the individual EC2 instances.
  2. Create an Amazon Elastic File System (Amazon EFS) file system. Mount the EFS file system on the individual EC2 instances. Correct Answer
  3. Create a shared Amazon Elastic Block Store (Amazon EBS) volume. Mount the EBS volume on the individual EC2 instances.
  4. Use AWS DataSync to perform continuous synchronization of data between EC2 hosts in the Auto Scaling group.
  5. Create an Amazon S3 bucket to store the web content. Set the metadata for the Cache-Control header to no-cache. Use Amazon CloudFront to deliver the content. Correct Answer

Key Takeaways

The exam tests the distinction between block/file storage capabilities across Availability Zones versus object storage patterns, specifically addressing the common trap of assuming EBS can be easily shared across AZs or that DataSync provides real-time synchronization.

This question evaluates the selection of scalable storage solutions for a multi-AZ web application requiring strong consistency and frequent updates. The correct options are Amazon EFS for shared file access and Amazon S3 combined with CloudFront for object-based content delivery.

Common mistake: Candidates often select C (EBS) because they overlook its AZ-local nature, or D (DataSync) due to misunderstanding its asynchronous replication model. They may also miss E because they fail to recognize S3's strong consistency and CloudFront's caching controls.

Expert Analysis

Why the Answer Is Correct

Option B is correct because Amazon EFS is a fully managed, elastic file system designed to scale automatically and provide concurrent access from multiple EC2 instances across different Availability Zones. It offers strong consistency semantics, ensuring that writes are immediately visible to subsequent reads, which meets the requirement for frequent content changes. Option E is correct because Amazon S3 now provides strong consistency for all operations, meaning new content is immediately available. By setting the Cache-Control header to 'no-cache' and using CloudFront, the solution ensures that edge caches do not serve stale content, effectively delivering fresh data as soon as it is uploaded to S3.

Why the Other Options Are Wrong

Option A is incorrect because AWS Storage Gateway Volume Gateway is primarily designed for hybrid cloud scenarios where on-premises applications access cloud storage via iSCSI, not for fully cloud-native multi-AZ scaling. Option C is incorrect because standard Amazon EBS volumes are attached to a single EC2 instance in one AZ; while Multi-Attach exists, it is limited to a single AZ and specific instance types, making it unsuitable for broad multi-AZ sharing. Option D is incorrect because AWS DataSync is an orchestration service for periodic data transfer, not a real-time continuous synchronization tool capable of handling frequent, immediate content updates.

Community Comment Notes

Community consensus strongly supports BE. User LeonSauveterre correctly noted that Volume Gateway is optimized for hybrid setups rather than fully cloud-based solutions. Another user emphasized that even with Multi-Attach, sharing EBS across AZs is complex and error-prone. User sandordini pointed out that DataSync cannot perform continuous synchronization between EC2 instances, only storage types. The majority voted for BE, aligning with the technical constraints of the scenario.

Exam Strategy

When asked about shared storage across multiple AZs, immediately consider EFS for files or S3 for objects. Avoid EBS unless the question explicitly specifies single-instance or same-AZ requirements. For caching questions, remember that 'strong consistency' in S3 is default, but you must manage CloudFront behavior via cache-control headers to ensure freshness.

Frequently Asked Questions

Can Amazon EBS be shared across multiple Availability Zones?

No, standard EBS volumes are bound to a single AZ. While EBS Multi-Attach allows multiple instances to attach, it is restricted to the same AZ and specific instance families.

Is AWS DataSync suitable for real-time content updates?

No, DataSync is designed for periodic, scheduled data transfers between endpoints. It does not provide the low-latency, continuous synchronization required for frequent web content changes.

More SAA-C03 FAQ →

Community Votes

BE
100%

100% of anonymous learners picked answer BE. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 7 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 7

  1. Cali182 👍 5
    B & E seems to be the most logic
  2. LeonSauveterre 👍 3
    A - Volume Gateway is typically on-prem and optimized for hybrid setups, not for fully cloud-based solutions. B - EFS provides a fully managed, shared file storage system that works across multiple AZs. C - Even with Multi-Attach, sharing EBS volumes across AZs is pretty complex and error-prone. D - DataSync is designed for periodic synchronization and not real-time, frequent updates. E - The "no-cache" header ensures the content is always fetched fresh, and CloudFront delivers it efficiently with reduced latency. Although S3 is less efficient for frequent updates compared to a shared file system like EFS, but not a problem here.
  3. sandordini 👍 2
    Regarding storage, I'd go for EFS, although it never mentions the requirement for file storage. Datasync can copy data between several storage types, including EFS, agents can be installed on EC2, but you cannot perform continuous synchronization of EC2 instances. Only storage. Cloudfront can publish both passive (s3) and active content (EC2+EFS) but wording doesn't tell a thing about such a share. And if it's a passive site why do we even have 2 storage types... I'd say, for me, the least bad solution seems to be B + E.
  4. alawada 👍 2
    BD looks most logical to me - continuous changes required an update via DataSync
  5. Penjerla 👍 1
    Option A is out as storage gateway is suited for hybrid cloud use cases where on-premises workloads need access to AWS cloud storage
Show 2 more comments
  1. Andy_09 👍 8
    Correct answer BE
  2. Hung23 👍 2
    I choose BE

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