Part I of this Deep Dive on containers introduces the idea of kernel control groups, or cgroups, and the way you can isolate, limit and monitor selected userspace applications. Here, I dive a bit deeper and focus on the next step of process isolation—that is, through containers, and more specifically, the Linux Containers (LXC) framework.
Containers are about as close to bare metal as you can get when running virtual machines. They impose very little to no overhead when hosting virtual instances. First introduced in 2008, LXC adopted much of its functionality from the Solaris Containers (or Solaris Zones) and FreeBSD jails that preceded it. Instead of creating a full-fledged virtual machine, LXC enables a virtual environment with its own process and network space. Using namespaces to enforce process isolation and leveraging the kernel's very own control groups (cgroups) functionality, the feature limits, accounts for and isolates CPU, memory, disk I/O and network usage of one or more processes. Think of this userspace framework as a very advanced form of chroot.
Note: LXC uses namespaces to enforce process isolation, alongside the kernel's very own cgroups to account for and limit CPU, memory, disk I/O and network usage across one or more processes.
But what exactly are containers? The short answer is that containers decouple software applications from the operating system, giving users a clean and minimal Linux environment while running everything else in one or more isolated "containers". The purpose of a container is to launch a limited set of applications or services (often referred to as microservices) and have them run within a self-contained sandboxed environment.
Note: the purpose of a container is to launch a limited set of applications or services and have them run within a self-contained sandboxed environment.
Figure 1. A Comparison of Applications Running in a Traditional Environment to Containers
This isolation prevents processes running within a given container from monitoring or affecting processes running in another container. Also, these containerized services do not influence or disturb the host machine. The idea of being able to consolidate many services scattered across multiple physical servers into one is one of the many reasons data centers have chosen to adopt the technology.
Container features include the following:
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