A system may include a deployment system configured to receive a request to upgrade a selected virtual machine (VM) of multiple VMs on a plurality of host machines from a first program code version to a second program code version, and, for each host machine, request an upgrade token. When the host machine acquires the upgrade token, the deployment system is configured to generate a snapshot of a code image associated with the second program code version, and provide the snapshot to the host machine via a virtual disk. The snapshot is stored on a storage device associated with a host machine or a server host machine. The snapshot may include metadata identifying a location of the code image on the storage device.