Using Docker

Chapter 1. The What and Why of Containers

Containers are fundamentally changing the way we develop, distribute, and run software. Developers can build software locally, knowing that it will run identically regardless of host environment—be it a rack in the IT department, a user’s laptop, or a cluster in the cloud. Operations engineers can concentrate on networking, resources, and uptime—and spend less time configuring environments and battling system dependencies. The use and uptake of containers is increasing at a phenomenal rate across the industry, from the smallest startups to large-scale enterprises. Developers and operations engineers should expect to regularly use containers in some fashion within the next few years.

Containers are an encapsulation of an application with its dependencies. At first glance, they appear to be just a lightweight form of virtual machines (VMs)—like a VM, a container holds an isolated instance of an operating system (OS), which we can use to run applications.

However, containers have several advantages that enable use cases that are difficult or impossible with traditional VMs:

• Containers share resources with the host OS, which makes them an order of magnitude more efficient. Containers can be started and stopped in a fraction of a second. Applications running in containers incur little to no overhead compared to applications running natively on the host OS.

• The portability of containers has the potential to eliminate a whole class of bugs ...