The correct choice is Amazon CloudWatch Logs. It is a managed service that can ingest system and application log files from Amazon EC2 instances and on prem servers, allow you to search log events, create metric filters, and drive CloudWatch alarms for near real time alerting to speed incident diagnosis.

Amazon CloudWatch Logs centralizes logs and supports agents and native integrations to collect logs from EC2 and on prem hosts. You can define metric filters that convert log patterns into CloudWatch metrics and then create alarms on those metrics so that alerts are triggered within roughly one minute for rapid investigation.

AWS CloudTrail records AWS API calls for auditing and compliance and does not serve as a general system or application log aggregation service or provide metric filters on arbitrary log content.

AWS X-Ray provides distributed request tracing and service maps to help debug latency and errors in applications and it is not designed for bulk log aggregation search or for creating CloudWatch metric filters from arbitrary logs.

Amazon OpenSearch Service is a powerful analytics and search engine for logs and metrics visualization but it requires an ingestion pipeline such as CloudWatch Logs subscriptions, Kinesis, or Firehose to receive logs. It does not by itself provide the native CloudWatch metric filter to alarm workflow that CloudWatch Logs does.

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