Amazon CloudWatch enables the monitoring of Amazon services, standard and custom defined metrics, and a variety of logs. Typically, you would want to retrieve metrics for analysis and/or integration with other monitoring tools. For example, you can use AWS Trusted Advisor to analyze your AWS configuration and usage, compare it to the best practices, and to alert you to opportunities to save on costs, help close security gaps, or improve system reliability and performance. CloudWatch provides APIs for retrieving hundreds of metrics by namespace, start and finish times, intervals, and so on.

CloudWatch logs can be monitored for errors, exceptions, HTTP response codes, Amazon S3 logs, and so on. In addition, you can also use the logs to correlate the system status with change events such as when AWS CloudFormation is used to rollout a new stack. We can define metric filters on the logs and raise alerts based on specific thresholds. These alerts can in turn be forwarded to SNS topics for appropriate notifications to be pushed out. The metric filters can be based on literal terms, common log formats, or specified using JSON. In addition, you can combine multiple literal terms, group the terms, count occurrences, and/or specify variable names for log record fields, and so on.

For monitoring API calls to AWS services, you can integrate AWS CloudTrail logs with AWS CloudWatch. You can also choose to receive SNS notifications from CloudWatch for the API activity captured by CloudTrail. Typically, you will turn on this integration from the CloudTrail console or through a CloudFormation template, define a metric filter for your CloudWatch Logs log group, assign a CloudWatch metric to the metric filter, and then create an appropriate CloudWatch alarm.

Other alternatives include subscribing to third-party logging services or rolling out your own solution for centralized monitoring. For example, you can use AWS Kinesis to ingest logging messages, an Elasticsearch cluster for searching through the records efficiently, and a product such as Kibana for visualization support. There are several third-party logging service providers such as Loggly, Splunk, Sumo Logic, and so on. You can subscribe to their services to meet your requirements (at scale).