How do you secure data at rest and in transit for AWS RDS?

AWS RDS secures data at rest primarily through encryption using AWS Key Management Service (KMS), and data in transit using SSL/TLS encryption, often enforced via database parameter groups.

Data at Rest

For data at rest, RDS integrates with KMS to encrypt the underlying storage, backups, snapshots, and read replicas. You can choose between AWS-managed keys, which provide transparent encryption with minimal overhead, or customer-managed keys (CMKs). CMKs offer greater control over key policies, rotation schedules, and access permissions, allowing you to manage the encryption lifecycle more granularly. This protects data against unauthorized physical access to storage and ensures data confidentiality even if storage volumes are compromised. Encryption is applied at the storage layer, meaning data is encrypted before it's written to disk and decrypted when read.

Data in Transit

For data in transit, SSL/TLS encrypts the communication channel between client applications and the RDS database instance. To enforce this, set the rds.force_ssl parameter to 1 in the associated DB parameter group. This mandates that all incoming connections must use SSL/TLS, rejecting unencrypted attempts. Foundational network security is provided by configuring Virtual Private Clouds (VPCs) and Security Groups to restrict database access to trusted IP ranges and resources. Additionally, IAM Database Authentication offers an alternative to traditional password-based authentication, leveraging IAM roles and users for database access, which centralizes credential management and improves auditing. While AWS Certificate Manager (ACM) manages certificates for many AWS services, RDS typically handles server-side certificates automatically; clients need to trust the AWS root CA.

For example, to enforce SSL on an RDS instance (e.g., PostgreSQL, MySQL), you would update its parameter group using the AWS CLI:

aws rds modify-db-parameter-group \
  --db-parameter-group-name my-rds-parameter-group \
  --parameters "ParameterName=rds.force_ssl,ParameterValue=1,ApplyMethod=immediate"

Using CMKs provides more granular control over encryption keys but adds management overhead; AWS-managed keys are simpler for many use cases.

In the interview, also mention regular credential rotation, leveraging CloudTrail for auditing database events and API calls, and utilizing Enhanced Monitoring for deeper visibility into OS-level metrics and potential security anomalies. Emphasize the principle of least privilege for IAM users and roles accessing RDS.