A company is migrating its two-tier legacy application (using MongoDB as a key-value database) from its on-premises data center to AWS. The company has mandated that the EC2 instances must be hosted in a private subnet with no internet access. In addition, all connectivity between the EC2 instance-hosted application and the database must be encrypted. The database must be able to scale to meet traffic spikes from any bursty or unpredictable workloads. Which do you recommend?