AWS ECS on Fargate vs EKS：スタートアップが3ヶ月で判断すべき7つの評価軸と実装コスト比較

ECS習得タイムライン:
Day 1-2: Dockerコンテナ化
Day 3-4: Terraformでタスク定義作成
Day 5-7: ALB統合、デプロイ自動化完了

EKS（別プロジェクトで経験）:
Week 1-2: Kubernetes基礎学習（Udemy/公式ドキュメント）
Week 3-4: EKS構築、ネットワーク設定で苦戦
Week 5-6: Ingress/Cert-Manager設定、デバッグ地獄
Week 7-8: ようやく本番投入...

- Fargate Task (0.5 vCPU, 1GB RAM) x 2台 24時間稼働
  → $35/月
- ALB (Application Load Balancer)
  → $23/月 + データ転送料 $10/月
- CloudWatch Logs (5GB/月)
  → $2.5/月
- RDS (db.t3.small)
  → $30/月
合計: 約 $100/月（約14,000円）

- EKSコントロールプレーン
  → $73/月（固定費）
- EC2ワーカーノード (t3.medium x 2台)
  → $60/月
- ALB
  → $23/月 + データ転送料 $10/月
- CloudWatch Logs
  → $2.5/月
- RDS (db.t3.small)
  → $30/月
合計: 約 $200/月（約28,000円）

# VPC、セキュリティグループ等は省略

# ECS Cluster
resource "aws_ecs_cluster" "main" {
  name = "my-startup-cluster"
}

# Task Definition
resource "aws_ecs_task_definition" "app" {
  family                   = "my-app"
  requires_compatibilities = ["FARGATE"]
  network_mode             = "awsvpc"
  cpu                      = "512"  # 0.5 vCPU
  memory                   = "1024" # 1GB

  execution_role_arn = aws_iam_role.ecs_execution_role.arn
  task_role_arn      = aws_iam_role.ecs_task_role.arn

  container_definitions = jsonencode([{
    name  = "app"
    image = "123456789012.dkr.ecr.ap-northeast-1.amazonaws.com/my-app:latest"

    portMappings = [{
      containerPort = 8080
      protocol      = "tcp"
    }]

    environment = [
      { name = "ENV", value = "production" }
    ]

    secrets = [
      {
        name      = "DATABASE_URL"
        valueFrom = aws_secretsmanager_secret.db_url.arn
      }
    ]

    logConfiguration = {
      logDriver = "awslogs"
      options = {
        "awslogs-group"         = "/ecs/my-app"
        "awslogs-region"        = "ap-northeast-1"
        "awslogs-stream-prefix" = "ecs"
      }
    }
  }])
}

# ECS Service
resource "aws_ecs_service" "app" {
  name            = "my-app-service"
  cluster         = aws_ecs_cluster.main.id
  task_definition = aws_ecs_task_definition.app.arn
  desired_count   = 2
  launch_type     = "FARGATE"

  network_configuration {
    subnets          = var.private_subnet_ids
    security_groups  = [aws_security_group.ecs_tasks.id]
    assign_public_ip = false
  }

  load_balancer {
    target_group_arn = aws_lb_target_group.app.arn
    container_name   = "app"
    container_port   = 8080
  }

  depends_on = [aws_lb_listener.app]
}

# Auto Scaling
resource "aws_appautoscaling_target" "ecs" {
  max_capacity       = 10
  min_capacity       = 2
  resource_id        = "service/${aws_ecs_cluster.main.name}/${aws_ecs_service.app.name}"
  scalable_dimension = "ecs:service:DesiredCount"
  service_namespace  = "ecs"
}

resource "aws_appautoscaling_policy" "ecs_cpu" {
  name               = "cpu-autoscaling"
  policy_type        = "TargetTrackingScaling"
  resource_id        = aws_appautoscaling_target.ecs.resource_id
  scalable_dimension = aws_appautoscaling_target.ecs.scalable_dimension
  service_namespace  = aws_appautoscaling_target.ecs.service_namespace

  target_tracking_scaling_policy_configuration {
    predefined_metric_specification {
      predefined_metric_type = "ECSServiceAverageCPUUtilization"
    }
    target_value = 70.0
  }
}

# EKS Cluster
resource "aws_eks_cluster" "main" {
  name     = "my-startup-cluster"
  role_arn = aws_iam_role.eks_cluster.arn
  version  = "1.28"

  vpc_config {
    subnet_ids              = concat(var.private_subnet_ids, var.public_subnet_ids)
    endpoint_private_access = true
    endpoint_public_access  = true
  }

  depends_on = [
    aws_iam_role_policy_attachment.eks_cluster_policy,
    aws_iam_role_policy_attachment.eks_vpc_resource_controller,
  ]
}

# Node Group
resource "aws_eks_node_group" "main" {
  cluster_name    = aws_eks_cluster.main.name
  node_group_name = "main-node-group"
  node_role_arn   = aws_iam_role.eks_nodes.arn
  subnet_ids      = var.private_subnet_ids

  scaling_config {
    desired_size = 2
    max_size     = 10
    min_size     = 2
  }

  instance_types = ["t3.medium"]

  depends_on = [
    aws_iam_role_policy_attachment.eks_worker_node_policy,
    aws_iam_role_policy_attachment.eks_cni_policy,
    aws_iam_role_policy_attachment.eks_container_registry_policy,
  ]
}

# IAM Roles（省略：ECS以上に複雑）
# ...

# OIDC Provider（EKSで必須）
data "tls_certificate" "eks" {
  url = aws_eks_cluster.main.identity[0].oidc[0].issuer
}

resource "aws_iam_openid_connect_provider" "eks" {
  client_id_list  = ["sts.amazonaws.com"]
  thumbprint_list = [data.tls_certificate.eks.certificates[0].sha1_fingerprint]
  url             = aws_eks_cluster.main.identity[0].oidc[0].issuer
}

# AWS Load Balancer Controller（Helmで別途インストール必要）
# Ingress設定（別途K8s YAMLで管理）
# ...

# deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 2
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: app
        image: 123456789012.dkr.ecr.ap-northeast-1.amazonaws.com/my-app:latest
        ports:
        - containerPort: 8080
        env:
        - name: ENV
          value: production
        # ...以下50行以上の設定
---
apiVersion: v1
kind: Service
metadata:
  name: my-app-service
spec:
  selector:
    app: my-app
  ports:
  - port: 80
    targetPort: 8080
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: my-app-ingress
  annotations:
    kubernetes.io/ingress.class: alb
    alb.ingress.kubernetes.io/scheme: internet-facing
# ...以下複雑な設定