---
id: devops-finops-cost
title: FinOps — Cloud cost / Tagging / 최적화
category: Coding
status: draft
source_trust_level: B
verification_status: conceptual
created_at: 2026-05-09
updated_at: 2026-05-09
tags: [devops, finops, cost, vibe-coding]
tech_stack: { language: "Terraform / AWS", applicable_to: ["DevOps"] }
applied_in: []
aliases: [FinOps, cloud cost, tagging, RI, savings plan, spot, rightsizing]
---

# FinOps

> Cloud bill 가 OOC (out of control). **Tag → cost allocation, RI / Savings Plan, spot, rightsizing, idle 제거** 5종. 보통 30-50% 절감 가능.

## 📖 핵심 개념
- Tag: 자원에 메타 (env, team, project).
- Cost allocation: tag 기반 청구.
- Reserved / Savings: 1년+ 약정 = 30-70% 할인.
- Spot: 대기 가능한 작업 = 70-90% 할인.

## 💻 코드 패턴

### Tagging strategy
```hcl
# Terraform — default tags
provider "aws" {
  default_tags {
    tags = {
      Environment = var.env
      Team        = var.team
      Project     = var.project
      CostCenter  = var.cost_center
      ManagedBy   = "terraform"
    }
  }
}
```

→ AWS Cost Explorer 가 tag 별 청구 분석.

### IAM 강제 — 미태그 금지
```json
{
  "Effect": "Deny",
  "Action": ["ec2:RunInstances", "rds:CreateDBInstance"],
  "Resource": "*",
  "Condition": {
    "Null": { "aws:RequestTag/Team": "true" }
  }
}
```

### 비용 모니터링
```ts
// AWS Cost Explorer API
const ce = new AWS.CostExplorer({ region: 'us-east-1' });
const r = await ce.getCostAndUsage({
  TimePeriod: { Start: '2026-05-01', End: '2026-05-09' },
  Granularity: 'DAILY',
  Metrics: ['UnblendedCost'],
  GroupBy: [{ Type: 'TAG', Key: 'Team' }],
}).promise();
```

```yaml
# Slack alert if cost spike
- alert: DailyCostSpike
  expr: aws_cost_today > 2 * aws_cost_avg_7d
```

### Reserved Instances / Savings Plans
```
On-demand:        $100/month
Reserved 1y:      $60 (40% off)
Reserved 3y:      $40 (60% off)
Savings Plan:     $50 (50% off, 더 유연)
```

→ 안정적 baseline = RI / SP. spike = on-demand.

### Spot instances
```hcl
resource "aws_instance" "worker" {
  instance_market_options {
    market_type = "spot"
    spot_options { max_price = "0.05" }
  }
}
```

→ 1-2분 알림 후 종료. Stateless / batch / autoscaling group.

```hcl
# K8s — Karpenter
provisioner:
  spec:
    requirements:
      - { key: karpenter.sh/capacity-type, operator: In, values: [spot, on-demand] }
```

### Rightsizing
```bash
# CloudWatch + Compute Optimizer
aws compute-optimizer get-ec2-instance-recommendations
# → "이 t3.large 는 t3.small 로 충분"
```

→ CPU / memory < 20% 사용 = 작게.

### Idle 자원 (가장 흔한 낭비)
```bash
# 미사용 EBS volumes
aws ec2 describe-volumes --filters Name=status,Values=available

# Idle ELB (no traffic)
# Stopped EC2 (EBS 비용 그대로)
# Old snapshots
aws ec2 describe-snapshots --owner-ids self --query 'Snapshots[?StartTime<`2025-01-01`]'

# Unused EIP
aws ec2 describe-addresses --filters Name=association-id,Values=
```

```bash
# 매일 정리
aws ec2 delete-volume --volume-id $UNATTACHED
```

### Scheduled scaling (dev)
```hcl
# Dev 환경 = 9-18 만 켜기 (50% 절감)
resource "aws_autoscaling_schedule" "off" {
  scheduled_action_name = "off-evening"
  recurrence            = "0 18 * * 1-5"
  desired_capacity      = 0
  ...
}

resource "aws_autoscaling_schedule" "on" {
  scheduled_action_name = "on-morning"
  recurrence            = "0 9 * * 1-5"
  desired_capacity      = 2
}
```

### Data transfer (숨은 비용)
```
Same-AZ: free
Cross-AZ: $0.01/GB
Cross-region: $0.02-0.09/GB
Internet egress: $0.05-0.09/GB

NAT gateway: $0.045/GB + $0.045/hour
→ VPC endpoint 로 S3 / DynamoDB 직접 (free)
```

### S3 storage class
```
Standard:        $23/TB/mo
Intelligent-Tier: 자동 전환
Standard-IA:     $12.5/TB/mo (가끔 access)
Glacier:         $4/TB/mo (long backup)
Glacier Deep:    $1/TB/mo (rare)
```

```hcl
resource "aws_s3_bucket_lifecycle_configuration" "main" {
  rule {
    status = "Enabled"
    transition { days = 30; storage_class = "STANDARD_IA" }
    transition { days = 90; storage_class = "GLACIER" }
  }
}
```

### Budget alarm
```hcl
resource "aws_budgets_budget" "monthly" {
  name         = "monthly"
  budget_type  = "COST"
  limit_amount = "10000"
  limit_unit   = "USD"
  time_unit    = "MONTHLY"
  
  notification {
    threshold = 80
    threshold_type = "PERCENTAGE"
    notification_type = "ACTUAL"
    subscriber_email_addresses = ["finance@acme.com"]
  }
}
```

### LLM cost (위 AI_LLM_Cost_Optimization)
```
LLM = 새로운 cloud bill. 별도 추적.
```

## 🤔 의사결정 기준
| 절감 영역 | 우선순위 |
|---|---|
| Idle 자원 | 즉시 (매주 cleanup) |
| Rightsizing | 월별 |
| Tag + visibility | 즉시 |
| RI / Savings | 6개월 안정 후 |
| Spot | Stateless 작업 |
| Data transfer | VPC endpoint |
| S3 lifecycle | 항상 |

## ❌ 안티패턴
- **Tag 없음**: cost 누구 책임 모름.
- **모든 자원 on-demand**: RI / SP 없으면 30-70% 더.
- **Dev 24h 켜둠**: 70% 낭비.
- **Spot prod stateful**: 강제 종료 시 데이터 잃음.
- **Snapshot / EBS / EIP 청소 X**: 매월 누적.
- **Cross-AZ 무절제**: $$$/GB.
- **Cost monitoring 없음**: 청구서 보고 놀람.

## 🤖 LLM 활용 힌트
- Tag → visibility → 액션.
- Idle 청소가 가장 ROI.
- Spot + Karpenter 자동.

## 🔗 관련 문서
- [[DevOps_Terraform_Patterns]]
- [[DevOps_Kubernetes_Basics]]
- [[AI_LLM_Cost_Optimization]]
