CloudWatch vs CloudTrail - What's the Difference and When to Use Each

CloudWatch and CloudTrail are two AWS services that sound similar but solve completely different problems. CloudWatch monitors the health and performance of your AWS resources, while CloudTrail records who did what in your AWS account and when.

If your Lambda function starts throwing errors, CloudWatch tells you about it. If someone changed your S3 bucket's encryption settings, CloudTrail tells you who made that change, from which IP address, and at what time.

This guide breaks down what each service does, shows you real console walkthroughs, and explains when to use one, the other, or both.

What is Amazon CloudWatch?

Amazon CloudWatch is a monitoring and observability service for AWS resources and the applications running on them. It collects metrics, aggregates logs, and triggers alarms based on thresholds you define.

CloudWatch answers questions like:

• Is my EC2 instance running out of memory?


• Why is my Lambda function timing out?


• How many 5xx errors did my API Gateway return in the last hour?


• Should my auto-scaling group add more instances?

Resource Monitoring with CloudWatch Metrics

CloudWatch automatically collects some performance metrics from AWS services, so EC2 instances report CPU utilization, network traffic, and disk I/O, while Lambda functions surface invocation count, duration, and error rate. RDS databases contribute connection count, read/write latency, and storage usage to the same metrics pipeline.

You can also push EC2 instance Monitoring tab showing default CloudWatch metrics including CPU utilization, network I/O, and credit usage

Centralized Logging with CloudWatch Logs

Beyond metrics, CloudWatch Logs centralizes log output from your workloads. EC2 instances, Lambda functions, ECS containers, and API Gateway all route logs into CloudWatch Log Groups, where each group contains log streams organized by source.

For example, a Lambda function creates a new log stream for each execution environment. An EC2 instance running the CloudWatch agent sends application logs to a log group you configure.

Viewing individual log events inside a CloudWatch log group

Threshold-Based Alerting with CloudWatch Alarms

With metrics and logs flowing in, the next step is acting on them. CloudWatch Alarms let you set thresholds on any metric and trigger actions when those thresholds are breached, whether that is sending a notification through SNS, triggering an Auto Scaling action, or invoking a Lambda function.

Each alarm has three states (OK, ALARM, and INSUFFICIENT_DATA), and you configure the evaluation period, comparison operator, and threshold value. For a full breakdown of alarm types and their costs, see the Creating a CloudWatch Alarm with metric selection, threshold configuration, and evaluation conditions

The overall flow in CloudWatch follows a pattern: metrics arrive from your resources, you visualize them in dashboards, set alarms on critical thresholds, and respond when something degrades.

What is AWS CloudTrail?

AWS CloudTrail is a governance and auditing service that records API activity across your AWS account. Monitorable actions taken through the AWS Console, CLI, SDK, or another AWS service generate an event in CloudTrail.

CloudTrail answers questions like:

• Who deleted that S3 bucket?


• When was this IAM role's permissions changed?


• Which IP address was used to modify the security group?


• Did anyone access this KMS key in the last 30 days?

Auditing Account Activity with CloudTrail Event History

By default, CloudTrail retains 90 days of management event history at no cost. Management events are control-plane operations like creating an EC2 instance, modifying an S3 bucket policy, or changing an IAM role. The event history table surfaces the fields that matter for investigations, including event name, timestamp, user name, event source, and affected resources.

CloudTrail event detail for a PutBucketEncryption action, showing identity, source IP, region, and event JSON

CloudTrail Trails and Long-Term Retention

The 90-day event history covers many investigation needs, but compliance and long-term auditing often require more. For retention beyond that window, you create a Trail that delivers events to an S3 bucket (and optionally to CloudWatch Logs), or use CloudTrail Lake to store event data for up to ~10 years with the one-year extendable retention option (or ~7 years with the seven-year retention option).

There are four types of events you can capture:

• 
  Management events: Control-plane operations (creating, deleting, or modifying resources). Enabled by default.


• 
  Data events: Data-plane operations (S3 object-level actions like GetObject and PutObject, Lambda invocations). Must be enabled explicitly.


• 
  Network activity events: VPC-related network actions. Also require explicit configuration.


• 
  Insights events: Unusual API call rates or error rates detected by CloudTrail Insights. Must be enabled on a trail.

CloudWatch vs CloudTrail: Side-by-Side Comparison

How CloudWatch and CloudTrail Work Together: A Practical Scenario

Consider this scenario: your team gets paged because a Lambda function's error rate spiked at 9:15 AM.

Step 1: CloudWatch tells you something is wrong.

CloudWatch Alarms fire because the Lambda error metric exceeded the configured threshold. You open CloudWatch Logs and see that the function is failing with AccessDeniedException when trying to read from an S3 bucket.

At this point, you know the symptom: the function lost access to S3. But CloudWatch cannot tell you why the permissions changed or who changed them.

Step 2: CloudTrail tells you what happened.

You open CloudTrail Event History and filter by the S3 bucket name. At 9:10 AM, five minutes before the errors started, you see a PutBucketPolicy event. The userIdentity field shows it was a team member's IAM user. The sourceIPAddress shows the request came from the office VPN.

Now you have the full picture: a bucket policy change at 9:10 AM removed the Lambda function's read access, causing the errors that CloudWatch detected at 9:15 AM.

This is why most teams need both services. CloudWatch catches the operational impact. CloudTrail provides the accountability trail.

Where SigNoz Fits in Your Observability Stack

: Logs Insights for log queries, the Metrics console for dashboards, X-Ray for traces, and Application Signals for service health. Each uses different query syntax, and clicking from metrics to logs resets your time filters. Finding logs for a trace requires copying trace IDs from X-Ray and running a separate search in CloudWatch Logs.

that eliminates this context-switching. Metrics, traces, and logs live in a single interface, so you can jump from a latency spike to the responsible trace to the related logs without leaving one screen.

CloudWatch's billing adds another friction point: log ingestion at $0.50/GB, custom metrics at $0.30/metric/month per dimension combination, Logs Insights charges of $0.005/GB scanned per query, and additional GetMetricData API charges when third-party tools poll metrics. SigNoz uses simple, usage-based pricing ($0.3/GB for logs and traces, $0.1/million metric samples) with no per-host charges or per-query fees.

For AWS-specific integrations, you can , and set up dedicated monitoring for , .

What SigNoz Does Not Replace

SigNoz does not replace CloudTrail, which remains the authoritative record for AWS account and API activity required for governance and compliance. No external observability platform substitutes that audit trail.

When a Lambda error spike appears in SigNoz, engineers verify runtime impact there, then check CloudTrail to confirm whether a recent IAM, S3, or API configuration change triggered it.

Get Started with SigNoz

You can choose between various deployment options in SigNoz. The easiest way to get started with SigNoz is .

Those who have the expertise to manage SigNoz themselves or just want to start with a free self-hosted option can use our .

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