Container, ie Docker container
A Docker Container is standardized software encapsulation environment that runs on a host computer. A container packages and isolates an application microservice - and any layers of software tools, configurations and libraries that this microservice depends on – into a replicable file (a single filesystem with a network namespace) that can run on any Linux server.
This enables portability to run on premises, public cloud, private cloud, or bare metal. All containers on a host computer are run by a single Linux operating system kernel. The median in 2018 surveys is 8 containers per host, but this can be 20 to 40 per hosts in many cases. The Docker daemon, called "dockerd" is a persistent Linux process that manages Docker containers. You can update an individual layer of a container. Thus containers are more lightweight - use fewer system resources and startup much faster - than virtual machines, each of which requires its own guest operating system and must be updated in total. A Docker service allows containers to be scaled across multiple Docker daemons. Containers can communicate with each other through a well-defined high-level API. Docker containers are integrated with and supported by infrastructure management and orchestration platforms and tools from virtually all vendors.