1. An apparatus, comprising: a processor; and a non-transitory computer-readable storage medium having instructions stored thereupon which are executable by the processor and which, when executed, cause the apparatus to expose a public web service application programming interface (API) within a service provider network, the API comprising a method for executing a custom command within a virtual machine (VM) instance executing in the service provider network, the custom command specified in a file; receive a call to the method for executing the custom command within the VM instance; and in response to receiving the call, cause a request to execute the custom command to be transmitted to a software agent executing in the VM instance, the software agent configured to read at least a portion of the file and execute the custom command in the VM instance in response to receiving the request.