A system, comprising: one or more processors; and memory including executable instructions that, when executed by the one or more processors, cause the system to: receive, at a managed directory service, from a customer of a computing resource service provider, an application programming interface call including a request to create a computer system directory within an isolated virtual network of the customer, the isolated virtual network of the customer hosted in a computing environment of the computing resource service provider, in accordance with one or more parameters specified by the customer; fulfill the received request by at least creating the computer system directory in the isolated virtual network of the customer, the computing system directory being inaccessible to computing resources of the computing resource service provider outside the isolated virtual network without provision of access by the managed directory service, so that the created computer system directory is configured to join, to the created computer system directory, virtual machines within the isolated virtual network to a domain of the computer system directory; and manage the created computer system directory on behalf of the customer. one or more processors; and memory including executable instructions that, when executed by the one or more processors, cause the system to: receive, at a managed directory service, from a customer of a computing resource service provider, an application programming interface call including a request to create a computer system directory within an isolated virtual network of the customer, the isolated virtual network of the customer hosted in a computing environment of the computing resource service provider, in accordance with one or more parameters specified by the customer; fulfill the received request by at least creating the computer system directory in the isolated virtual network of the customer, the computing system directory being inaccessible to computing resources of the computing resource service provider outside the isolated virtual network without provision of access by the managed directory service, so that the created computer system directory is configured to join, to the created computer system directory, virtual machines within the isolated virtual network to a domain of the computer system directory; and manage the created computer system directory on behalf of the customer. receive, at a managed directory service, from a customer of a computing resource service provider, an application programming interface call including a request to create a computer system directory within an isolated virtual network of the customer, the isolated virtual network of the customer hosted in a computing environment of the computing resource service provider, in accordance with one or more parameters specified by the customer; fulfill the received request by at least creating the computer system directory in the isolated virtual network of the customer, the computing system directory being inaccessible to computing resources of the computing resource service provider outside the isolated virtual network without provision of access by the managed directory service, so that the created computer system directory is configured to join, to the created computer system directory, virtual machines within the isolated virtual network to a domain of the computer system directory; and manage the created computer system directory on behalf of the customer.