AWS Cost Explorer Guide

Gain full visibility into your AWS spend with Cost Allocation Tags, Cost Anomaly Detection, and the Cost Explorer API. Cut costs by finding idle resources, rightsizing instances, and committing to Savings Plans with data.

Step 1 — Activate Cost Allocation Tags

Tags must be activated in the Billing console before they appear in Cost Explorer. Navigate to Billing → Cost allocation tags → AWS-generated tags and activate aws:createdBy. Then activate your user-defined tags.

# Tag enforcement via AWS Config rule (detect untagged resources)
aws configservice put-config-rule --config-rule '{
  "ConfigRuleName": "required-tags",
  "Source": {
    "Owner": "AWS",
    "SourceIdentifier": "REQUIRED_TAGS"
  },
  "InputParameters": "{\"tag1Key\":\"Environment\",\"tag2Key\":\"Team\",\"tag3Key\":\"Project\"}"
}'

# Tag all EC2 instances in a region using tag-editor (console) or CLI
aws ec2 describe-instances --query 'Reservations[*].Instances[*].InstanceId' \
  --output text | xargs -I {} aws ec2 create-tags \
  --resources {} \
  --tags Key=Environment,Value=production Key=Team,Value=platform

Recommended Tag Schema

Step 2 — Cost Anomaly Detection Setup

# Create a monitor for all AWS services
aws ce create-anomaly-monitor --anomaly-monitor '{
  "MonitorName": "AllServicesMonitor",
  "MonitorType": "DIMENSIONAL",
  "MonitorDimension": "SERVICE"
}'

# Create an alert subscription (SNS + email)
aws ce create-anomaly-subscription --anomaly-subscription '{
  "SubscriptionName": "DailyAnomalyAlert",
  "MonitorArnList": ["arn:aws:ce::123456789012:anomalymonitor/MONITOR_ID"],
  "Subscribers": [
    {
      "Address": "[email protected]",
      "Type": "EMAIL"
    },
    {
      "Address": "arn:aws:sns:us-east-1:123456789012:cost-alerts",
      "Type": "SNS"
    }
  ],
  "Threshold": 100,
  "Frequency": "DAILY"
}'

Step 3 — Savings Plans Purchase via CLI

# View Savings Plan recommendations
aws savingsplans describe-savings-plans-offering-rates \
  --savings-plan-offering-ids <offering-id> \
  --filters '[{"name":"tenancy","values":["Shared"]}]'

# Get hourly commitment recommendation for 1-year Compute Savings Plan
aws ce get-savings-plans-purchase-recommendation \
  --savings-plans-type COMPUTE_SP \
  --term-in-years ONE_YEAR \
  --payment-option NO_UPFRONT \
  --lookback-period-in-days SIXTY_DAYS

# Purchase a Savings Plan ($10/hour commitment, 1-year, no upfront)
aws savingsplans create-savings-plan \
  --savings-plan-offering-id <offering-id> \
  --commitment 10.00 \
  --client-token "purchase-$(date +%s)"

Step 4 — Cost Explorer API Automation

import boto3
from datetime import datetime, timedelta
import json

ce = boto3.client('ce', region_name='us-east-1')

def get_daily_cost_by_team(days=30):
    end = datetime.today().strftime('%Y-%m-%d')
    start = (datetime.today() - timedelta(days=days)).strftime('%Y-%m-%d')

    response = ce.get_cost_and_usage(
        TimePeriod={'Start': start, 'End': end},
        Granularity='DAILY',
        Filter={
            'Tags': {
                'Key': 'Environment',
                'Values': ['production']
            }
        },
        GroupBy=[{'Type': 'TAG', 'Key': 'Team'}],
        Metrics=['UnblendedCost']
    )
    return response['ResultsByTime']

# Get top services by cost this month
def get_top_services():
    today = datetime.today()
    start = today.replace(day=1).strftime('%Y-%m-%d')
    end = today.strftime('%Y-%m-%d')

    response = ce.get_cost_and_usage(
        TimePeriod={'Start': start, 'End': end},
        Granularity='MONTHLY',
        GroupBy=[{'Type': 'DIMENSION', 'Key': 'SERVICE'}],
        Metrics=['UnblendedCost']
    )
    groups = response['ResultsByTime'][0]['Groups']
    sorted_groups = sorted(groups,
        key=lambda x: float(x['Metrics']['UnblendedCost']['Amount']),
        reverse=True)
    for g in sorted_groups[:10]:
        print(f"{g['Keys'][0]}: ${float(g['Metrics']['UnblendedCost']['Amount']):.2f}")

get_top_services()

Monthly Cost Review Checklist

• Check Cost Anomaly Detection alerts from prior 30 days
• Review top 5 services by cost — any unexpected growth?
• Run EC2 rightsizing recommendations in Cost Explorer
• Check Savings Plan utilization — target >90%
• Identify untagged resources via AWS Config or Tag Editor
• Review idle RDS instances (0 connections over 7 days)
• Check S3 storage lens for buckets with no reads in 90 days
• Review NAT Gateway costs — often a surprise top-5 service