In computer programming, a runtime system, also called runtime environment, primarily implements portions of an execution model. This is not to be confused with the runtime lifecycle phase of a program, during which the runtime system is in operation.

Control Groups have been around for a while as well: the code was started in 2006, and initially merged in kernel 2.6.24.

So while they do not play a role in preventing one container from accessing or affecting the data and processes of another container, they are essential to fend off some denial-of-service attacks. They are particularly important on multi-tenant platforms, like public and private PaaS, to guarantee a consistent uptime (and performance) even when some applications start to misbehave.

Control Groups are another key component of Linux Containers. They implement resource accounting and limiting. They provide many useful metrics, but they also help ensure that each container gets its fair share of memory, CPU, disk I/O; and, more importantly, that a single container cannot bring the system down by exhausting one of those resources.

And there is more: the design and inspiration for the namespaces code are even older. Namespaces are actually an effort to reimplement the features of OpenVZ in such a way that they could be merged within the mainstream kernel. And OpenVZ was initially released in 2005, so both the design and the implementation are pretty mature.

How mature is the code providing kernel namespaces and private networking? Kernel namespaces were introduced between kernel version 2.6.15 and 2.6.26. This means that since July 2008 (date of the 2.6.26 release ), namespace code has been exercised and scrutinized on a large number of production systems.

When you specify public ports for your containers or use links then IP traffic is allowed between containers. They can ping each other, send/receive UDP packets, and establish TCP connections, but that can be restricted if necessary. From a network architecture point of view, all containers on a given Docker host are sitting on bridge interfaces. This means that they are just like physical machines connected through a common Ethernet switch; no more, no less.

Of course, if the host system is setup accordingly, containers can interact with each other through their respective network interfaces — just like they can interact with external hosts.

Each container also gets its own network stack, meaning that a container doesn’t get privileged access to the sockets or interfaces of another container.

Docker containers are very similar to LXC containers, and they have similar security features. When you start a container with docker run, behind the scenes Docker creates a set of namespaces and control groups for the container.

Namespaces provide the first and most straightforward form of isolation: processes running within a container cannot see, and even less affect, processes running in another container, or in the host system.

Containers allow running multiple applications in isolation. It is lightweight and use operating system of the host. It starts quickly, usually in seconds. Furthermore, it needs less hardware resources.

Container is an isolated environment for running an application. Virtual machine is an abstraction of a machine or physical hardware.

Docker is a platform for building, running and shipping applications.

In 2013, Docker introduced what would become the industry standard for containers. Containers are a standardized unit of software that allows developers to isolate their app from its environment, solving the “it works on my machine” headache. For millions of developers today, Docker is the de facto standard to build and share containerized apps - from desktop, to the cloud. We are building on our unique connected experience from code to cloud for developers and developer teams.

Following this evolution, Docker continues to give back with the containerd project, which Docker donated to the Cloud Native Computing Foundation (CNCF) in 2017. containerd is an industry-standard container runtime that leverages runc and was created with an emphasis on simplicity, robustness and portability. containerd is the core container runtime of the Docker Engine.

Docker open sourced libcontainer and partnered with a worldwide community of contributors to further its development. In June 2015, Docker donated the container image specification and runtime code now known as runc, to the Open Container Initiative (OCI) to help establish standardization as the container ecosystem grows and matures.

The launch of Docker in 2013 jump started a revolution in application development - by democratizing software containers. Docker developed a Linux container technology - one that is portable, flexible and easy to deploy.

Virtual machines (VMs) are an abstraction of physical hardware turning one server into many servers. The hypervisor allows multiple VMs to run on a single machine. Each VM includes a full copy of an operating system, the application, necessary binaries and libraries - taking up tens of GBs. VMs can also be slow to boot.

Containers are an abstraction at the app layer that packages code and dependencies together. Multiple containers can run on the same machine and share the OS kernel with other containers, each running as isolated processes in user space. Containers take up less space than VMs (container images are typically tens of MBs in size), can handle more applications and require fewer VMs and Operating systems.

Technology available from Docker and its open source project, Moby has been leveraged by all major data center vendors and cloud providers. Many of these providers are leveraging Docker for their container-native IaaS offerings. Additionally, the leading open source serverless frameworks utilize Docker container technology.

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