Q: Design a cost-optimized cloud architecture for an internal reporting app that runs every night and stores logs for 3 years.

Do not run continuous virtual machines. Use AWS Batch or Azure Container Instances (ACI) / Azure Functions running on Spot compute instances (up to 80-90% discount). A scheduled cloud timer (AWS EventBridge / Azure Logic Apps) triggers the container job at 2:00 AM; the compute spins down to exactly $0.00 upon job completion.

# Terraform: Schedule AWS EventBridge rule to trigger ephemeral Batch job
resource "aws_cloudwatch_event_rule" "nightly_report" {
  name                = "nightly-batch-reporting"
  schedule_expression = "cron(0 2 * * ? *)"
}

If a relational database is required, deploy Amazon Aurora Serverless v2 or Azure SQL Database Serverless with auto-pause enabled (`min_capacity = 0`). The database automatically sleeps when idle and resumes only during the nightly reporting execution window.

Because logs are required for 3-year compliance and rarely queried, stream raw compressed JSON/Parquet logs directly to object storage with an aggressive lifecycle transition policy: - **Days 1-30**: Standard S3 / Blob Storage (fast audit access if immediate issues arise). - **Day 31**: Transition to Glacier Flexible / Cold Tier. - **Day 90 to Year 3**: Transition to S3 Glacier Deep Archive ($0.00099 per GB/month) or Azure Archive Storage. - **Day 1096**: Automated deletion rule.

# S3 Lifecycle Rule for 3-Year Compliance
resource "aws_s3_bucket_lifecycle_configuration" "log_retention" {
  bucket = aws_s3_bucket.reporting_logs.id
  rule {
    id     = "3-year-compliance-archive"
    status = "Enabled"
    transition {
      days          = 30
      storage_class = "GLACIER_IR"
    }
    transition {
      days          = 90
      storage_class = "DEEP_ARCHIVE"
    }
    expiration {
      days = 1096
    }
  }
}

Enable S3 Object Lock or Azure Immutable Blob Storage in Compliance Mode to guarantee that logs cannot be deleted or overwritten by anyone (including root accounts) for the mandatory 3-year statutory audit period.