A customer utilizes an interface provided by a virtual computer system service to provision a virtual machine instance and join this instance to a directory. The interface may have previously obtained the domain name and the Internet Protocol addresses for one or more directories available to the customer for joining the virtual machine instance. The virtual computer system service may communicate with a managed directory service to obtain a set of temporary credentials that may be used to transmit a request to the directory to allow joining of the virtual machine instance. Upon provisioning of the instance, an agent operating within the instance may be configured to obtain the domain name and Internet Protocol addresses for the directory to establish a connection with the directory. The agent may also be configured to obtain the set of temporary credentials to transmit a request to the directory for joining of the instance.