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Docker makes it easy for developers to develop and deploy apps inside neatly packaged virtual containerized environments. PayPal has over 700+ applications now, and they have converted them all into container-based applications. PayPal, MetLife and MetLife are using Docker to boost their dev productivity by 50%. Docker is a form of virtualization, but unlike the virtual machines, the resources are shared directly with the host. This allows you to run many Docker containers where you may only be able to run a few virtual machines.