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AWS FinOps Field Notes: Cutting Non-Production RDS Multi-AZ Cost Waste

#aws #python #finops #database

While auditing cloud infrastructure costs this week, recurring configuration gaps continue to quietly inflate monthly bills.

Field Insight: The Hidden Cost Trap

Multi-AZ is an exact 100% cost markup (2x hourly compute plus 2x provisioned storage) for synchronous standby failover instances. A single db.r6g.xlarge on PostgreSQL costs about $0.52/hour ($380/month) in Single-AZ versus about $1.04/hour ($760/month) in Multi-AZ, so staging and dev clusters running Multi-AZ 24/7 waste $380/month ($4,560/year) per instance on failover redundancy that is never used during development.

Automated Detection: Auditing Non-Production RDS Multi-AZ Instances with Boto3 

import boto3

def audit_rds_dev_instances(region='us-east-1'):
    rds = boto3.client('rds', region_name=region)
    instances = rds.describe_db_instances().get('DBInstances', [])
    flagged = []
    for db in instances:
        if not db.get('MultiAZ'):
            continue
        db_id = db['DBInstanceIdentifier']
        arn = db.get('DBInstanceArn', '')
        tags = {}
        if arn:
            tags = {t['Key']: t['Value'] for t in
                    rds.list_tags_for_resource(ResourceName=arn).get('TagList', [])}
        env = tags.get('env', tags.get('Environment', ''))
        flagged.append({'DBInstance': db_id, 'Environment': env})
        print(f"[ALERT] {db_id} runs Multi-AZ (2x cost) in env '{env or 'untagged'}'. "
              f"Non-production instances rarely need synchronous standby failover.")
    print(f"[{region}] Multi-AZ RDS instances: {len(flagged)}")
    return flagged

if __name__ == '__main__':
    audit_rds_dev_instances()
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