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The copilot can query AWS Cost Explorer data to break down spend by service, region, and account, identify cost trends, detect anomalies, drill into resource-level costs, and forecast future spend. Use it to answer billing questions, investigate cost spikes, and find optimization opportunities without leaving the chat interface.

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Prerequisites

AWS Account with Cost Access

Connect an AWS account with Cost Explorer API access enabled. The IAM role used by Kestrel needs ce:GetCostAndUsage, ce:GetCostForecast, and related Cost Explorer permissions.
AWS Cost Explorer data is typically delayed by 24–48 hours. The copilot returns the most recent data available, but today’s costs may not be fully reflected yet.

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Targeting Accounts

Use @cloud:connection-name to query costs for a specific AWS account. You can target multiple accounts for cross-account comparisons. 
@cloud:prod-aws What are our top 10 services by cost this month?

@cloud:prod-aws @cloud:staging-aws Compare total spend across both accounts for the last 3 months.
If you have only one AWS account connected, the copilot targets it automatically.

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Spend Breakdown

Query costs by service, region, account, or any combination. 
@cloud:prod-aws What are our top 10 most expensive AWS services this month? Compare to last month and flag any that increased by more than 20%.

@cloud:prod-aws Break down our EC2 costs by region for the last 30 days. Which region is the most expensive?

@cloud:prod-aws How much are we spending on data transfer this month? Break it down by service and transfer type (inter-region, internet, etc.).

@cloud:prod-aws What's our total RDS spend? Break it down by instance, and include the instance type and engine for each.

@cloud:prod-aws Show me a cost breakdown for the last month grouped by the "team" cost allocation tag. Which team is spending the most?
Track how costs change over days, weeks, and months. 
@cloud:prod-aws How has our total AWS spend changed month-over-month for the last 6 months? What's the growth rate?

@cloud:prod-aws Show me the daily EC2 spend for the last 30 days. Were there any days with unusual spikes?

@cloud:prod-aws Compare our Lambda costs between Q4 last year and Q1 this year. Did the migration to ARM functions reduce costs?

@cloud:prod-aws What's the trend for our S3 storage costs over the last 3 months? Is it growing linearly or accelerating?

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Anomaly Detection

Identify unusual cost patterns and unexpected charges. 
@cloud:prod-aws Are there any unusual cost spikes in the last 7 days? What services are driving them?

@cloud:prod-aws Which services had the biggest percentage increase in cost compared to the previous month? Flag anything over 30% growth.

@cloud:prod-aws Did anything unexpected happen with our NAT Gateway costs last week? They seem higher than usual.

@cloud:prod-aws Show me any new services or regions that appeared on our bill this month that weren't there last month.

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Resource-Level Costs

Drill into specific resources to understand cost drivers. 
@cloud:prod-aws Which RDS instances cost the most? Include instance type, storage, and whether they're Multi-AZ.

@cloud:prod-aws Estimate how much we'd save if we right-sized all EC2 instances in us-east-1 that have averaged less than 15% CPU utilization over the last 30 days.

@cloud:prod-aws Which Elastic IPs are allocated but not associated with a running instance? How much are they costing us?

@cloud:prod-aws What are the most expensive EBS volumes? Flag any that are unattached or over-provisioned relative to their utilization.

@cloud:prod-aws How much are we spending on idle or underutilized load balancers?

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Forecasting

Project future costs based on current trends. 
@cloud:prod-aws What's our projected total AWS spend for next month based on current usage patterns?

@cloud:prod-aws At the current growth rate, what will our EC2 costs be in 3 months? What about 6 months?

@cloud:prod-aws What's our projected EKS spend for the next quarter based on current trends? Break it down by cluster if possible.

@cloud:prod-aws If we continue at the current data transfer rate, what will our CloudFront costs be next month?

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Cross-Account Comparison

Compare costs across multiple AWS accounts. 
@cloud:prod-aws @cloud:staging-aws Compare total monthly spend across both accounts for the last 3 months. How much is staging costing relative to production?

@cloud:prod-aws @cloud:staging-aws @cloud:dev-aws What's the cost per environment for EC2 and RDS? Are non-production environments disproportionately expensive?

@cloud:prod-aws @cloud:staging-aws Are we running the same instance types in staging as production? If staging is using larger instances, how much would we save by right-sizing?

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Example Conversation

You:
@cloud:prod-aws Our AWS bill jumped 30% this month. What’s going on?
Kestrel:
Your total AWS spend for the current month is 47,200,upfrom47,200, up from 36,300 last month (+30%). The top 3 drivers of the increase:
  1. EC2 — up $5,800 (+28%). Three new m5.2xlarge instances were launched in us-west-2 on the 15th. They’re running in the analytics account and aren’t part of any Auto Scaling group.
  2. RDS — up $3,100 (+41%). The prod-analytics instance had a storage auto-scaling event that grew it from 500GB to 1.2TB. There was also a class change from db.r5.large to db.r5.2xlarge on the 8th.
  3. NAT Gateway — up $2,000 (+62%). Data processing through the NAT gateway in us-east-1 doubled compared to last month, likely from the new batch processing jobs.
You:
Can we save money on those EC2 instances? They might be over-provisioned.
Kestrel:
Based on CloudWatch metrics for the last 2 weeks, the three m5.2xlarge instances in us-west-2 average 12% CPU utilization and 4.2GB of memory usage (out of 32GB available). You have a few options:
  • Right-size to m5.large: Saves ~$4,200/month. The instances would still have headroom at 48% average CPU and 8GB memory.
  • Switch to Spot: These aren’t in an ASG but could tolerate interruption if they’re batch analytics jobs. Spot pricing for m5.2xlarge in us-west-2 is currently 67% cheaper.
  • Reserved Instances: If you need them long-term, a 1-year no-upfront RI for m5.large would save an additional 30% on top of right-sizing.
You:
Let’s right-size them to m5.large. Can you find the Terraform code?
Kestrel:
The instances are defined in acme/infrastructure/terraform/analytics/ec2.tf. Here’s the proposed change to update all three from m5.2xlarge to m5.large: (displays Terraform diff with Create PR and Copy options)

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Next Steps