Alex, a cloud security engineer working in Eyecloud Inc. is tasked with isolating applications from the underlying infrastructure and stimulating communication via well-defined channels. For this purpose, he used an open-source technology that helped him in developing, packaging, and running applications; further, the technology provides PaaS through OS-level virtualization, delivers containerized software packages, and promotes fast software delivery.
What is the cloud technology employed by Alex in the above scenario?

A. Virtual machine
B. Docker
C. Zero trust network
D. Serverless computing