When the OpenNebula project started in 2008, we intended to create an open solution to make Enterprise Cloud simple. From the beginning, we understood enterprise cloud computing as en evolution of data center virtualization to host both cloud-aware and traditional applications. So we aimed to combine existing virtualization technologies with multi-tenancy, automatic provision and elasticity, following a bottom-up approach driven by the real-life needs of sysadmins and devops, and the following main principles.