AWS ECS Fargate 跑 Chatwoot + Dify

为什么选 Fargate#

• 不管 EC2，按 vCPU + GB 秒费
• 自动扩缩，闲时几乎不花钱
• 但比 EC2 自建贵 30-50%，适合不想运维的小团队

推荐架构#

Terraform 骨架#

module "ecs" {
  source = "terraform-aws-modules/ecs/aws"
  cluster_name = "ai-support"
  
  fargate_capacity_providers = {
    FARGATE      = { default_capacity_provider_strategy = { weight = 50 } }
    FARGATE_SPOT = { default_capacity_provider_strategy = { weight = 50 } }
  }
}

resource "aws_ecs_service" "chatwoot" {
  name            = "chatwoot-rails"
  cluster         = module.ecs.cluster_id
  task_definition = aws_ecs_task_definition.chatwoot.arn
  desired_count   = 2
  launch_type     = "FARGATE"
}

resource "aws_appautoscaling_target" "chatwoot" {
  max_capacity       = 10
  min_capacity       = 2
  resource_id        = "service/${module.ecs.cluster_name}/chatwoot-rails"
  scalable_dimension = "ecs:service:DesiredCount"
  service_namespace  = "ecs"
}

成本估算#

资源	配置	月费
Fargate（每 Task）	0.5 vCPU / 1 GB	~$15
Fargate Spot 折扣	-50%
RDS PG db.t3.medium	—	~$80
ElastiCache r6g.large	—	~$80
ALB	—	~$20
S3 + 流量	—	~$30
典型中小生产		~$300/月

提示：50% 任务跑 Fargate Spot 能省 25-40%。

自动扩缩策略#

# 按 CPU 70% 扩缩
TargetTrackingScalingPolicy:
  TargetValue: 70
  PredefinedMetricSpecification:
    PredefinedMetricType: ECSServiceAverageCPUUtilization

三个 AWS 特有的坑#

1. Task 启动慢：Fargate 冷启动 30-60s，promo 流量到达前要预热
2. Spot 中断：Fargate Spot 任务可能 2 分钟提前通知后被回收，配 SIGTERM 优雅退出
3. NAT 网关贵：私有子网出公网调 LLM 走 NAT，按 GB 计费；流量大时用 VPC Endpoint 走 PrivateLink