Amazon Web Services SAA-C03 Online Access

Sporadic HTTP 500 errors in an application that depends on DynamoDB often indicate intermittent downstream failures (for example, transient throttling, temporary network issues, request timeouts, or service-side retryable exceptions). The prompt notes that the DynamoDB table is in on-demand mode and other applications use it without problems, which suggests the issue is not a sustained capacity shortfall or a systemic DynamoDB outage. Instead, the web application likely needs to handle occasional retryable failures more gracefully.

Option C is the best practice for improving reliability when calling AWS services: implement exponential backoff with retries. AWS SDKs commonly include retry behavior, but many systems still require tuning (for example, increasing maximum retries, adding jitter, ensuring idempotent operations where required, and retrying only on retryable errors). Exponential backoff reduces the chance of overwhelming a service during brief contention periods and helps the application recover quickly from transient errors without user-visible failures. This approach is also minimally disruptive because it is a configuration and logic improvement rather than an architectural migration.

Option A is not a standard DynamoDB configuration; DynamoDB has item size limits and throughput is managed via on-demand or provisioned capacity, not by “supporting larger write requests.” Option B (Streams) provides a change data capture feed but does not prevent or mitigate request failures; it is for event processing, replication, or auditing. Option D (strongly consistent reads) addresses stale reads, not HTTP 500 errors, and could increase read cost/RCU consumption without solving the root cause.

Therefore, adding exponential backoff and retries is the most appropriate and operationally sound way to reduce sporadic failures without disrupting the application’s architecture or performance.

The Amazon CloudWatch agent is required to collect memory utilization metrics (as memory metrics are not reported by default). A target tracking policy is the simplest and most effective way to scale based on a custom metric such as mem_used_percent.

Reference Extract:

" Install the CloudWatch agent to collect memory metrics, and create a target tracking scaling policy using these custom metrics. "

Source: AWS Certified Solutions Architect – Official Study Guide, Monitoring and Scaling section.

Amazon EFS provides a shared, elastic, low-latency file system that can be mounted concurrently by many EC2 instances across multiple Availability Zones, delivering strong read-after-write consistency so all instances see updates almost immediately. This is the standard pattern for CMS-style workloads that require shared, up-to-date assets with minimal lag. Syncing local copies from S3 (C) introduces polling windows and eventual consistency delays; hourly sync is not near-real time. Copying from a “newest instance” (A) is brittle and not scalable. EBS volumes/snapshots (D) are single-instance, single-AZ block devices and not designed for multi-writer sharing across instances/AZs. EFS’s multi-AZ design and POSIX semantics provide the simplest, most reliable solution with the least operational overhead.

You cannot encrypt an existing unencrypted RDS DB instance in place. AWS guidance for encrypting an existing RDS PostgreSQL instance is totake a snapshot, create an encrypted copy of that snapshot, and restore a new DB instance from the encrypted snapshot. AWS also documents that encryption uses AWS KMS keys and that customer managed keys are the appropriate choice when you want explicit control over the key used for the new encrypted instance. That makesBthe required migration step andEthe correct key-management step. Option C is invalid because encryption cannot simply be turned on for the existing instance, and option D is not how you create a new AWS-managed default key.

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