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Cloud and Container Basics

Among the Linux kernel features that make containers possible, which of the following correctly pairs namespaces and cgroups (control groups) with their roles?

  1. ANamespaces: separate what a process can see (process IDs, network, mounts, etc.); cgroups: limit and account for the use of resources such as CPU and memory
  2. BNamespaces: limit and account for the use of resources such as CPU and memory; cgroups: separate what a process can see (process IDs, network, mounts, etc.)
  3. CNamespaces: boot a separate kernel for each container to isolate them; cgroups: create a virtual CPU for each container and emulate the hardware
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Answer: A. Namespaces: separate what a process can see (process IDs, network, mounts, etc.); cgroups: limit and account for the use of resources such as CPU and memory

A container is an ordinary process running on the host kernel, isolated by two mechanisms. Namespaces split process IDs, the network, mounts (the view of the file system), the host name and so on into groups, so that the processes in a container see only their own share. Cgroups limit the CPU time and amount of memory a group of processes can use and account for their usage. Both are kernel features, so a container neither boots another kernel nor emulates hardware.

  • A. Correct. Namespaces handle "what is visible" and cgroups handle "how much can be used".
  • B. The roles are swapped. Cgroups limit the amount of resources, and namespaces separate the view.
  • C. Running a separate kernel or emulating hardware is how virtual machines on a hypervisor work. Containers share the host kernel.
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