Understanding AWS Cost Explorer

One of the great benefits of the AWS cloud is its pay-as-you-go pricing model. But with hundreds of services and complex pricing dimensions, understanding your monthly bill can be a challenge. How do you know where your money is going? How can you find opportunities to save?

The primary tool that AWS provides to answer these questions is AWS Cost Explorer.

What is AWS Cost Explorer?

AWS Cost Explorer is a free tool that lets you visualize, understand, and manage your AWS costs and usage over time. It provides a default report that shows your costs for the last few months and a forecast for the coming month, but its real power lies in its ability to create custom reports and dive deep into your spending data.

To use Cost Explorer, you must first enable it in the AWS Billing console. Once enabled, it can take up to 24 hours for your data to become available.

Key Features of Cost Explorer

1. Pre-configured Reports

Cost Explorer provides several pre-configured views to get you started:

• Monthly costs: A high-level overview of your spending.
• Daily costs: A more granular view to spot daily spikes.
• Costs by service: See which AWS services (e.g., EC2, S3, RDS) are contributing most to your bill.
• Costs by linked account: If you use AWS Organizations, you can see the costs for each account.

2. Filtering and Grouping

This is where the real power of Cost Explorer lies. You can filter and group your cost and usage data by a wide range of dimensions:

• Service: Group by service to see your top cost drivers.
• Region: See which geographic regions are costing you the most.
• Usage Type: Get very granular by looking at specific usage types, like DataTransfer-Out-Bytes or BoxUsage:t3.micro.
• Tags: This is one of the most powerful features. If you have a good tagging strategy for your resources, you can filter and group your costs by project, team, or application. For example, you can see the total cost for all resources tagged with Project: Phoenix.

3. Cost and Usage Reports

Cost Explorer allows you to build custom reports to analyze your data. You can choose:

• Time Period: Analyze your costs over a specific date range.
• Granularity: View your costs on a monthly, daily, or hourly basis.
• Chart Type: Visualize your data as a bar chart or a line chart.

Once you've created a report that is useful to you, you can save it for future use.

4. Forecasting

Cost Explorer uses your historical usage data to forecast your likely spend for the rest of the month. This can help you identify if you are on track to go over budget and take corrective action early.

A Common Use Case: Finding an Unexpected Cost Spike

Imagine you notice that your bill for this month is higher than usual.

1. Open Cost Explorer and set the granularity to Daily.
2. You see a large spike in costs that started three days ago.
3. You Group by Service and see that the spike is coming from EC2.
4. You add a filter for the EC2 service and then Group by Usage Type.
5. You discover that the cost is coming from a large number of c5.2xlarge instances that you weren't expecting.
6. You then Group by Tag (assuming you have a 'user' or 'project' tag) and identify who launched these instances.

This workflow allows you to quickly diagnose the root cause of unexpected costs.

Conclusion

Managing costs is a critical part of operating in the cloud. AWS Cost Explorer is an essential tool that provides the visibility you need to understand where your money is going. By regularly reviewing your costs, creating custom reports, and using tags to attribute costs to projects and teams, you can gain control over your AWS spend and identify opportunities for optimization. It's the foundation of a good FinOps (Cloud Financial Operations) practice.