Option A is the most correct because it provides both : (1) automated patching and (2) compliance monitoring
/enforcement across a fleet, using AWS-native services built for exactly this purpose.
* AWS Systems Manager Patch Manager is designed to automate patching of managed instances using patch baselines , maintenance windows (or on-demand), and it produces compliance status for patching. It's the standard AWS service to apply OS/security patches at scale without SSH'ing into instances.
* AWS Config can be used to evaluate and track compliance over time against defined rules, giving centralized visibility and continuous compliance assessment. With remediation , Config can invoke Systems Manager Automation documents to correct non-compliant resources or trigger patch actions (depending on the rule/remediation design). This meets the "monitor and enforce" requirement.
Why the other options don't meet requirements as well:
* B is manual, doesn't scale well, and increases operational risk (key management, human error). It's not
"automated monitoring and enforcement."
* C (replacing instances with new AMIs) can be part of an immutable infrastructure strategy, but by itself it does not provide compliance monitoring across the current fleet, and scaling policies based on CloudWatch metrics are unrelated to patch compliance. Also, patch cadence would depend on AMI pipelines and instance rotation rather than direct compliance enforcement.
* D is operationally heavy and mismatched: CloudTrail records API activity; it does not natively provide "patch compliance" status for instance OS packages. Recreating instances via CloudFormation for every patch is not an efficient or standard enforcement mechanism for patch compliance.

Using CodePipeline + CodeConnections Git repo provides version control, automated deployment, and rollback. Each template includes AWS::ControlTower::EnableControl for OU-level guardrails. AWS Control Tower documentation recommends this GitOps automation model.

When a Lambda function processes an SQS batch and a subset of messages fail, the default behavior re- queues the entire batch, causing already-successfully-processed messages to be delivered and processed again.
The ReportBatchItemFailures feature in the Lambda event source mapping allows the function to return a partial failure response, indicating only the specific message IDs that failed. Lambda then deletes the successfully processed messages from the queue and re-queues only the failed items, preventing duplicate processing of successful messages. This approach maintains high concurrency because it does not restrict parallelism. Setting batch size to 1 (Option B) avoids batching entirely but eliminates the concurrency and throughput benefits. Reserved concurrency of 1 (Option D) severely restricts scalability. A 1-second batch window (Option A) affects how long Lambda waits to form a batch but does not prevent duplicate processing.

When using the awslogs log driver with Amazon ECS on EC2, CloudWatch Logs permissions must be granted to the ECS container instance IAM role , not the task definition or infrastructure role. The ECS agent running on the EC2 instances is responsible for creating log streams and pushing log events to Amazon CloudWatch Logs on behalf of the containers.
In this scenario, the task definition is correctly configured to automatically create the log group (awslogs- create-group: true) and send logs to the specified Region. However, the error occurs because the EC2 container instances do not have sufficient IAM permissions to perform the required CloudWatch Logs API calls. As a result, ECS cannot place the task, and it reports that no container instance meets the requirements.
According to AWS documentation, the container instance IAM role must include the following permissions when using the awslogs driver:
* logs:CreateLogStream
* logs:PutLogEvents
* (and, when creating log groups automatically) logs:CreateLogGroup
Option C correctly addresses the root cause by updating the container instance IAM role . Option A is incorrect because the ECS infrastructure or service role is not used to write logs. Option B is unrelated to permissions and does not resolve the issue. Option D would fail because the log group does not already exist, causing task startup to fail.
Therefore, modifying the container instance IAM role is the correct solution.

https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/metrics-collected-by-CloudWatch-agent.
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