Amazon DocumentDB is an AWS-managed document database service compatible with the MongoDB 3.6 API, allowing users to leverage automated database management and scaling by AWS. The service provides visibility into key metrics and logs from database clusters through integration with Datadog, enabling monitoring of cluster health, performance, and costs. A DocumentDB cluster consists of EC2 instances and a storage volume that replicates data across availability zones, ensuring high availability and security features such as instance running in Amazon VPC environments. The service offers various metrics for tracking resource utilization, volume usage, and throughput to optimize cluster scaling and cost management. Additionally, Datadog's integration provides audit logging capabilities to monitor cluster events and automate log sending from CloudWatch Logs to Datadog.