Docker offers a new, lightweight approach to application portability. Applications are shipped using a common container format and managed with a high-level API. Their processes run within isolated namespaces that abstract the operating environment independently of the distribution, versions, network setup, and other details of this environment. This «containerization» has often been nicknamed «the new virtualization.» But containers are more than lightweight virtual machines. Beyond their smaller footprint, shorter boot times, and higher consolidation factors, they also bring a lot of new features and use cases that were not possible with classical virtual machines.