Secret backends are connected to which of the following?

Secret backends in HashiCorp Vault are specifically designed to interface with different types of storage solutions where secrets can be stored and managed. The focus on various database plug-ins is particularly relevant because these plug-ins allow Vault to interact directly with various database systems to read and write secrets, manage credentials, and handle sensitive information dynamically.

Using database plug-ins, Vault can generate database credentials dynamically that are time-bound and assigned to specific users or applications. This approach not only enhances security by limiting access to secrets but also allows for easier management and rotation of credentials. The integration with database systems thus maximizes Vault's capability to secure and manage sensitive data across different environments and use cases.

In contrast, while internal caching systems, external cloud services, and backup services may be relevant to other aspects of Vault or data management, they do not serve as the primary connection point for secret backends in the context of storing and managing secrets. Vault’s strongest use cases are built around its ability to securely interface with different databases through specialized plug-ins.