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Docker is an open-source project that automates the deployment of applications inside software containers, by providing an additional layer of abstraction and automation of operating-system-level virtualization on Linux. Docker uses resource isolation features of the Linux kernel such as cgroups and kernel namespaces to allow independent "containers" to run within a single Linux instance, avoiding the overhead of starting and maintaining virtual machines. The Linux kernel's support for namespaces mostly isolates an application's view of the operating environment, including process trees, network, user IDs and mounted file systems, while the kernel's cgroups provide resource isolation, including the CPU, memory, block I/O and network. Since version 0.9, Docker includes the library as its own way to directly use virtualization facilities provided by the Linux kernel, in addition to using abstracted virtualization interfaces via libvirt, LXC (Linux Containers) and systemd-nspawn.〔(【引用サイトリンク】 libcontainer - reference implementation for containers )〕 According to industry analyst firm 451 Research, "Docker is a tool that can package an application and its dependencies in a virtual container that can run on any Linux server. This helps enable flexibility and portability on where the application can run, whether on premises, public cloud, private cloud, bare metal, etc." == Overview == Docker implements a high-level API to provide lightweight containers that run processes in isolation. Building on top of facilities provided by the Linux kernel (primarily cgroups and namespaces), a Docker container, unlike a virtual machine, does not require or include a separate operating system.〔 Instead, it relies on the kernel's functionality and uses resource isolation (CPU, memory, block I/O, network, etc.) and separate namespaces to isolate the application's view of the operating system. Docker accesses the Linux kernel's virtualization features either directly using the library, which is available since Docker 0.9, or indirectly via , LXC (Linux Containers) or .〔 By using containers, resources can be isolated, services restricted, and processes provisioned to have an almost completely private view of the operating system with their own process ID space, file system structure, and network interfaces. Multiple containers share the same kernel, but each container can be constrained to only use a defined amount of resources such as CPU, memory and I/O. Using Docker to create and manage containers may simplify the creation of highly distributed systems, by allowing multiple applications, worker tasks and other processes to run autonomously on a single physical machine or across multiple virtual machines. This allows the deployment of nodes to be performed as the resources become available or when more nodes are needed, allowing a platform as a service (PaaS)-style of deployment and scaling for systems like Apache Cassandra, MongoDB or Riak. Docker also simplifies the creation and operation of task or workload queues and other distributed systems. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Docker (software)」の詳細全文を読む スポンサード リンク
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