A first computer transmits a respective first command to each of a plurality of second computer systems. Each first command includes instructions to initiate one or more virtual machine instances on the respective second computer system. Each virtual machine instance is configured to retrieve data from a third computer system over a communications network, cache the retrieved data, and transmit the cached data to one or more client computers over the communications network in response to a request for the cached data by the one or more client computers. The first computer system also transmits configuration data to each of the second computer systems. The configuration data includes indications of one or more parameters associated with retrieving the data from the third computer system, caching the retrieved data, and/or transmitting the cached data to the one or more client computers.