Container Compose File Format
Introduction
Most container runtimes now support some kind of container composition format to
define one or more containers and their configurations each.
This greatly simplifies the starting up, and orchestrating of
containers based on a set specification.
This all started with Docker's implementing its docker-compose program and
compose file format.
Or as Docker puts it in their compose file format specification:
The Compose Specification lets you define a platform-agnostic container based application. Such an application is designed as a set of containers which have to both run together with adequate shared resources and communication channels.
Basics
The format of a compose file is now largely converged on an improved version of Docker's original compose file. That is it's a YAML file format with reserved keys for each expected configuration.