AWS Cost Optimization: 10 Terraform Patterns to Cut Your Bill by 40%

# Stop RDS outside business hours using EventBridge scheduler
resource "aws_lambda_function" "rds_scheduler" {
  filename      = "rds_scheduler.zip"
  function_name = "rds-cost-scheduler"
  role          = aws_iam_role.rds_scheduler.arn
  handler       = "index.handler"
  runtime       = "python3.12"
}

# Stop at 8 PM weekdays
resource "aws_cloudwatch_event_rule" "stop_rds" {
  name                = "stop-dev-rds"
  schedule_expression = "cron(0 20 ? * MON-FRI *)"
}

resource "aws_cloudwatch_event_target" "stop" {
  rule  = aws_cloudwatch_event_rule.stop_rds.name
  arn   = aws_lambda_function.rds_scheduler.arn
  input = jsonencode({ action = "stop", identifier = "dev-aurora-cluster" })
}

# Start at 7 AM weekdays
resource "aws_cloudwatch_event_rule" "start_rds" {
  name                = "start-dev-rds"
  schedule_expression = "cron(0 7 ? * MON-FRI *)"
}

resource "aws_cloudwatch_event_target" "start" {
  rule  = aws_cloudwatch_event_rule.start_rds.name
  arn   = aws_lambda_function.rds_scheduler.arn
  input = jsonencode({ action = "start", identifier = "dev-aurora-cluster" })
}

# Billing alarm
resource "aws_cloudwatch_metric_alarm" "billing_alert" {
  alarm_name          = "monthly-billing-alert"
  comparison_operator = "GreaterThanThreshold"
  evaluation_periods  = 1
  metric_name         = "EstimatedCharges"
  namespace           = "AWS/Billing"
  period              = 86400
  statistic           = "Maximum"
  threshold           = 200
  alarm_actions       = [aws_sns_topic.billing_alerts.arn]

  dimensions = {
    Currency = "USD"
  }
}