When working with AWS infrastructure, two services play essential roles in monitoring and management: Amazon CloudWatch and AWS CloudTrail.
Although both are essential, they fulfill distinct roles. This guide will explore the differences between CloudWatch and CloudTrail, when to use each, and how they apply to key AWS services like S3, DynamoDB, API Gateway, and EC2. We will also delve into access logs and execution logs, two critical concepts for tracking the performance and functionality of your services.

What is AWS CloudWatch?

Amazon CloudWatch is a monitoring service that helps you track performance and operational health across your AWS infrastructure and applications. It collects metrics, logs, and events, and allows you to set alarms based on specific thresholds.

CloudWatch is particularly useful for monitoring resource usage—such as CPU utilization, memory usage, and disk I/O—as well as detecting errors and performance issues in AWS services like EC2, Lambda, and API Gateway. With CloudWatch, you can visualize data in dashboards to gain real-time insights into your infrastructure’s health.

What is AWS CloudTrail?

AWS CloudTrail is a service that tracks and logs API activity in your AWS account. It records who took actions, what they did, when it happened, and where the request came from. CloudTrail is essential for maintaining a record of changes for governance, security audits, and compliance purposes.

Every time an API call is made to an AWS service, CloudTrail records that action. This makes it a valuable tool for tracking changes, ensuring compliance, and investigating security incidents by providing a detailed history of API calls.

CloudWatch vs. CloudTrail: Key Differences

CloudWatch and CloudTrail may seem similar because they both log activity, but they serve very different purposes. CloudWatch focuses on monitoring performance and operational metrics, while CloudTrail focuses on auditing API activity and tracking changes to your AWS resources.

CloudWatch:

• Tracks performance metrics like CPU usage, memory, and network traffic.
• Collects and monitors logs from AWS services and custom applications.
• Allows you to set alarms to detect issues (e.g., when disk space is running low).

CloudTrail:

• Tracks API activity, logging details of who performed actions, what was done, and when.
• Provides detailed records for auditing, security investigations, and compliance.
• Useful for tracking configuration changes to AWS resources.

When to Use CloudWatch vs. CloudTrail

You should use CloudWatch when you need to monitor the operational health of your resources. This includes tracking performance metrics, setting alarms, and monitoring logs. For example, if you need to monitor CPU usage on an EC2 instance or request counts on an API Gateway, CloudWatch is the tool for the job. It helps you stay on top of system performance and quickly address issues as they arise.

On the other hand, you should use CloudTrail when you need to audit API activity or investigate who made changes to your AWS resources. CloudTrail is ideal for tracking security events, ensuring compliance, and creating an audit trail. For example, if you want to find out who deleted an S3 object or who changed the configuration of a DynamoDB table, CloudTrail provides the detailed logs needed to track down this information.

CloudWatch Logs: Access Logs vs. Execution Logs

In CloudWatch, logs are critical for gaining visibility into the behavior of your services. Two types of logs often collected for services like API Gateway are access logs and execution logs.

Access Logs:

• These logs capture high-level information about who accessed your API or service. They include details such as IP addresses, HTTP methods (GET, POST, etc.), and status codes (e.g., 200 OK or 404 Not Found).

• Access logs help you monitor traffic patterns and see if your services are being accessed correctly. They provide a high-level overview of who is using your service and whether their requests are being successfully fulfilled.

Execution Logs:

• Execution logs offer a deeper level of detail by capturing the entire flow of requests inside the API or service. They include request payloads, response payloads, and any errors encountered during the processing of the request.

• These logs are essential for debugging and troubleshooting. They help you understand what went wrong when a request fails and why certain responses are returned.

For example, if your API Gateway encounters an error during a request, execution logs will show the request payload, the internal processing of that request, and the error message returned. This allows you to investigate and resolve issues faster.

Use Cases for CloudWatch and CloudTrail Across AWS Services

Let’s take a look at how CloudWatch and CloudTrail apply to specific AWS services like S3, DynamoDB, API Gateway, and EC2.

Amazon S3

CloudWatch is used to monitor the operational metrics of your S3 buckets, such as the number of requests made, the amount of data transferred, and the overall size of the storage. It’s particularly helpful when you want to keep an eye on how your S3 bucket is performing or set up alarms if the number of errors exceeds a certain threshold. For example, you might want to know if there’s a spike in 4xx or 5xx errors and get notified automatically.

On the other hand, CloudTrail provides detailed logs of API activity in S3. It records actions such as who accessed the bucket, who created or deleted objects, and when those actions occurred. CloudTrail is essential for auditing API activity and tracking who made changes to your data, which is particularly useful for compliance and security purposes. If you need to investigate who deleted a file from your bucket, CloudTrail will tell you exactly who did it and when.

Amazon DynamoDB

For DynamoDB, CloudWatch tracks performance metrics such as read/write capacity usage, throttled requests, and latency. This allows you to monitor your DynamoDB tables to ensure they are performing optimally. If your tables are being overused and you risk hitting the provisioned capacity limits, you can set up CloudWatch alarms to notify you when throttling occurs.

Meanwhile, CloudTrail tracks API actions related to DynamoDB, such as table creation, deletion, data modification, and read requests. This is useful for auditing who made changes to your tables and when. For example, if you need to find out who modified a table schema or deleted a specific record, CloudTrail provides the necessary logs.

API Gateway

For API Gateway, CloudWatch plays a key role in monitoring request rates, latency, and error rates. It also collects both access logs and execution logs. The access logs allow you to see who accessed your API and the execution logs provide detailed insights into what happens when your API processes a request, including request and response payloads and any errors.

In contrast, CloudTrail logs changes to the API itself, such as adding new routes, deploying new stages, or deleting APIs. If you want to know who made changes to your API configuration, CloudTrail provides a detailed history of those actions.

EC2 Instances

CloudWatch monitors EC2 performance metrics such as CPU usage, memory usage, disk I/O, and network traffic. You can also collect system logs, application logs, and security logs from EC2 instances using CloudWatch, but this requires some manual setup. To collect these logs, you need to install and configure the CloudWatch Agent on your EC2 instances, which allows you to capture logs beyond the basic metrics.

CloudTrail, on the other hand, logs API activity related to EC2, such as starting, stopping, or terminating instances, as well as modifying security groups. If you need to track who launched or terminated an instance or who made changes to the security group settings, CloudTrail is the tool for the job.

Manual Setup for CloudWatch on EC2

While basic EC2 metrics such as CPU and network usage are automatically available in CloudWatch, log collection from the operating system or applications requires manual configuration. You’ll need to install the CloudWatch Agent on your EC2 instances and configure it to send logs (such as system logs or application logs) to CloudWatch Logs. This manual setup enables detailed logging beyond the default performance metrics.

Conclusion

In summary, both CloudWatch and CloudTrail are essential tools for managing your AWS environment, but they serve different purposes. CloudWatch focuses on monitoring performance metrics and operational health, helping you track resource utilization, detect issues, and set alarms. CloudTrail, on the other hand, is crucial for auditing API activity and tracking who made changes to your AWS resources, making it invaluable for security and compliance.

By combining CloudWatch for performance monitoring and CloudTrail for auditing, you can maintain a robust and well-monitored AWS environment. Whether you’re tracking CPU usage in EC2, monitoring request rates in API Gateway, or investigating who modified data in DynamoDB