Option D is correct because migrating the application to a virtual machine (VM) on Compute Engine and using an instance schedule to manage the VM's operation times aligns with the need for minimal effort and cost. This approach is suitable for long-running tasks like data analytics, which runs for a specific duration each night. Compute Engine VMs can handle the workload efficiently without the need for additional container orchestration or serverless platforms that may not be optimized for such tasks. Options A, B, and C involve more complex setups or platforms not ideal for long-running processes, making them less efficient and potentially more costly for this scenario.