Containers are a form of operating system-level virtualization. They are logical partitions within a host's operating system that allow an application and its dependencies to be packaged together. Each container runs as an isolated process in user space on the host operating system's kernel. This isolation is achieved through kernel features like namespaces (which provide the container with its own view of the network, process tree, etc.) and control groups (cgroups), which limit the amount of host resources (CPU, memory) the container can consume. This makes them lightweight and efficient compared to traditional virtual machines.

C. Is a software like a VM.

Containers virtualize the operating system, not the underlying hardware like a Virtual Machine (VM), and they share the host OS kernel.

D. No limited access to resources.

Containers use kernel control groups (cgroups) to explicitly limit and manage access to system resources like CPU, memory, and I/O.

1. Official Vendor Documentation: Nokia's technical documentation on its cloud-native platforms, such as Nokia Container Services (NCS), describes containers as lightweight, standalone, executable packages that include everything needed to run an application and are isolated from one another, sharing the host system’s OS kernel. This aligns with containers being isolated (B) logical spaces (A). (Reference: Nokia Container Services (NCS) Product Documentation, Release 21, "NCS Overview" section).

2. Peer-reviewed Academic Publication: P. R. P. Santos, J. P. B. de Souza, F. R. de Sousa, and R. P. D. Justo, "An Updated Review on Container-based Virtualization," IEEE Access, vol. 7, pp. 169311-169333, 2019. In Section II-A, "Container Technology," the paper states, "Containers are isolated environments that run on top of a single host kernel... Isolation is provided by two main features of the Linux kernel: namespaces and control groups (cgroups)." This directly supports that containers are isolated (B) and have limited resources (refuting D). DOI: https://doi.org/10.1109/ACCESS.2019.2953978

3. University Courseware: Stanford University, CS 244B: Distributed Systems, Winter 2021, Lecture 11: "Virtualization, Containers, and Serverless." The lecture notes differentiate containers from VMs, explaining that containers are "isolated environments within an OS" that "share the host OS kernel," contrasting with VMs that "virtualize hardware." This supports options A and B while refuting option C. (Reference: Stanford CS 244B, Lecture 11 Slides, Slides 25-30).