AWS Architecture Patterns for High-Growth SaaS Products

Infrastructure architecture decisions compound. The choice you make about compute in week one of a new service shapes your deployment patterns, scaling strategy, and operational overhead for years. Most early-stage SaaS products are over-architected for resilience and under-architected for cost.

VPC Design That Doesn't Get You in Trouble

• Three AZs, always: Single-AZ is a time bomb. The cost of a second and third AZ is trivial compared to the cost of an outage during an AWS AZ failure.
• Public subnets for load balancers only: ALB goes in the public subnet. Everything else — ECS tasks, RDS, ElastiCache — goes in private subnets with NAT Gateway egress.
• NAT Gateway per AZ: One shared NAT Gateway is a single point of failure and a bandwidth bottleneck. Spend the extra $35/month per AZ.
• VPC endpoints for S3 and DynamoDB: Free, eliminates NAT Gateway charges for S3 traffic (often 20–30% of NAT costs for media-heavy products).

From $3,200 to $780: The Real Changes

• Moved nightly batch jobs from always-on EC2 to ECS Scheduled Tasks: Saved $420/month. The EC2 instance ran 24/7 to execute 3-hour jobs.
• Right-sized RDS: The client was running db.r6g.xlarge (16GB RAM) for a 2GB database. Moved to db.t4g.medium with read replica. Saved $380/month.
• CloudFront in front of S3: Eliminated $290/month in S3 request costs. CloudFront's regional edge cache absorbed 94% of asset requests.
• Deleted 847GB of unattached EBS volumes and unused snapshots: $180/month of pure waste from terminated instances nobody cleaned up.

# Terraform — ECS service with blue/green deployment
resource "aws_ecs_service" "api" {
  name            = "api-service"
  cluster         = aws_ecs_cluster.main.id
  task_definition = aws_ecs_task_definition.api.arn
  desired_count   = 3

  deployment_controller {
    type = "CODE_DEPLOY"
  }

  load_balancer {
    target_group_arn = aws_lb_target_group.blue.arn
    container_name   = "api"
    container_port   = 3000
  }

  health_check_grace_period_seconds = 30
}