Software applications typically depend on other libraries, configuration files, or services that are provided by the runtime environment. The traditional runtime environment for a software application is a physical host or virtual machine, and application dependencies are installed as part of the host.

For example, consider a Python application that requires access to a common shared library that implements the TLS protocol. Traditionally, a system administrator installs the required package that provides the shared library before installing the Python application.

The major drawback to a traditionally deployed software applications is that the application's dependencies are entangled with the runtime environment. An application may break when any updates or patches are applied to the base operating system (OS).

For example, an OS update to the TLS shared library removes TLS 1.0 as a supported protocol. This breaks the deployed Python application because it is written to use the TLS 1.0 protocol for network requests. This forces the system administrator to roll back the OS update to keep the application running, preventing other applications from using the benefits of the updated package.

Therefore, a company developing traditional software applications may require a full set of tests to guarantee that an OS update does not affect applications running on the host.

Furthermore, a traditionally deployed application must be stopped before updating the associated dependencies. To minimize application downtime, organizations design and implement complex systems to provide high availability of their applications. Maintaining multiple applications on a single host often becomes cumbersome, and any deployment or update has the potential to break one of the organization's applications.

A container image is a lightweight, stand-alone, executable package of a piece of software that includes everything needed to run it: code, runtime, system tools, system libraries, settings.

Containerization based on virtualization allows any application bundled in a container that can be run without the hassles of any dependency like libraries. They are a kind of isolated partition inside a single operating system.

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