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update swarm worker node concept description 

incorporated review comments from Misty

re-worded topic titles and added to description of node

fixed links for services and tasks

incorporated more comments

Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>
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Victoria Bialas 2017-01-03 18:51:07 -08:00
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engine/swarm/key-concepts.md
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@ -7,37 +7,40 @@ title: Swarm mode key concepts
This topic introduces some of the concepts unique to the cluster management and This topic introduces some of the concepts unique to the cluster management and
orchestration features of Docker Engine 1.12. orchestration features of Docker Engine 1.12.
## Swarm ## What is a swarm?
The cluster management and orchestration features embedded in the Docker Engine The cluster management and orchestration features embedded in the Docker Engine
are built using **SwarmKit**. Engines participating in a cluster are are built using **SwarmKit**. Docker engines participating in a cluster are
running in **swarm mode**. You enable swarm mode for the Engine by either running in **swarm mode**. You enable swarm mode for an engine by either
initializing a swarm or joining an existing swarm. initializing a swarm or joining an existing swarm.
A **swarm** is a cluster of Docker Engines where you deploy A **swarm** is a cluster of Docker engines, or _nodes_, where you deploy
[services](key-concepts.md#Services-and-tasks). The Docker Engine CLI includes the commands for [services](key-concepts.md#services-and-tasks). The Docker Engine CLI and API
swarm management, such as adding and removing nodes. The CLI also includes the include commands to manage swarm nodes (e.g., add or remove nodes), and deploy
commands you need to deploy services to the swarm and manage service and orchestrate services accross the swarm.
orchestration.
When you run Docker Engine outside of swarm mode, you execute container When you run Docker without using swarm mode, you execute container
commands. When you run the Engine in swarm mode, you orchestrate services. commands. When you run the Docker in swarm mode, you orchestrate services. You can run swarm services and standalone containers on the same Docker instances.
## Node ## What is a node?
A **node** is an instance of the Docker Engine participating in the swarm. A **node** is an instance of the Docker engine participating in the swarm. You can also think of this as a Docker node. You can run one or more nodes on a single physical computer or cloud server, but production swarm deployments typically include Docker nodes distributed across multiple physical and cloud machines.
To deploy your application to a swarm, you submit a service definition to a To deploy your application to a swarm, you submit a service definition to a
**manager node**. The manager node dispatches units of work called **manager node**. The manager node dispatches units of work called
[tasks](key-concepts.md#Services-and-tasks) to worker nodes. [tasks](key-concepts.md#services-and-tasks) to worker nodes.
Manager nodes also perform the orchestration and cluster management functions Manager nodes also perform the orchestration and cluster management functions
required to maintain the desired state of the swarm. Manager nodes elect a single leader to conduct orchestration tasks. required to maintain the desired state of the swarm. Manager nodes elect a
single leader to conduct orchestration tasks.
**Worker nodes** receive and execute tasks dispatched from manager nodes. By **Worker nodes** receive and execute tasks dispatched from manager nodes.
default manager nodes are also worker nodes, but you can configure managers to By default manager nodes also run services as worker nodes, but you can
be manager-only nodes. The agent notifies the manager node of the current configure them to run manager tasks exclusively and be manager-only
state of its assigned tasks so the manager can maintain the desired state. nodes. An agent runs on each worker node and reports on the tasks assigned to
it. The worker node notifies the manager node of the current state of its
assigned tasks so that the manager can maintain the desired state of each
worker.
## Services and tasks ## Services and tasks