Merge pull request #25817 from sfsmithcha/update_glossary

add swarm mode terms to the glossary

docs/reference/glossary.md

@@ -19,7 +19,7 @@ aufs (advanced multi layered unification filesystem) is a Linux [filesystem](#fi
 Docker supports as a storage backend. It implements the
 [union mount](http://en.wikipedia.org/wiki/Union_mount) for Linux file systems.
 
-## Base image
+## base image
 
 An image that has no parent is a **base image**.
 
@@ -153,6 +153,16 @@ installs Docker on them, then configures the Docker client to talk to them.
 
 *Also known as : docker-machine*
 
+## node
+
+A [node](../swarm/how-swarm-mode-works/nodes.md) is a physical or virtual
+machine running an instance of the Docker Engine in swarm mode.
+
+**Manager nodes** perform swarm management and orchestration duties. By default
+manager nodes are also worker nodes.
+
+**Worker nodes** execute tasks.
+
 ## overlay network driver
 
 Overlay network driver provides out of the box multi-host network connectivity
@@ -181,15 +191,54 @@ labeled using [tags](#tag).
 Here is an example of the shared [nginx repository](https://hub.docker.com/_/nginx/)
 and its [tags](https://hub.docker.com/r/library/nginx/tags/)
 
+
+## service
+
+A [service](../swarm/how-swarm-mode-works/services.md) is the definition of how
+you want to run your application containers in a swarm. At the most basic level
+a service  defines which container image to run in the swarm and which commands
+to run in the container. For orchestration purposes, the service defines the
+"desired state", meaning how many containers to run as tasks and constraints for
+deploying the containers.
+
+Frequently a service is a microservice within the context of some larger
+application. Examples of services might include an HTTP server, a database, or
+any other type of executable program that you wish to run in a distributed
+environment.
+
+## service discovery
+
+Swarm mode [service discovery](../swarm/networking.md) is a DNS component
+internal to the swarm that automatically assigns each service on an overlay
+network in the swarm a VIP and DNS entry. Containers on the network share DNS
+mappings for the service via gossip so any container on the network can access
+the service via its service name.
+
+You don’t need to expose service-specific ports to make the service available to
+other services on the same overlay network. The swarm’s internal load balancer
+automatically distributes requests to the service VIP among the active tasks.
+
+## swarm
+
+A [swarm](../swarm/index.md) is a cluster of one or more Docker Engines running in [swarm mode](#swarm-mode).
+
 ## Swarm
 
-[Swarm](https://github.com/docker/swarm) is a native clustering tool for Docker.
-Swarm pools together several Docker hosts and exposes them as a single virtual
-Docker host. It serves the standard Docker API, so any tool that already works
-with Docker can now transparently scale up to multiple hosts.
+Do not confuse [Docker Swarm](https://github.com/docker/swarm) with the [swarm mode](#swarm-mode) features in Docker Engine.
+
+Docker Swarm is the name of a standalone native clustering tool for Docker.
+Docker Swarm pools together several Docker hosts and exposes them as a single
+virtual Docker host. It serves the standard Docker API, so any tool that already
+works with Docker can now transparently scale up to multiple hosts.
 
 *Also known as : docker-swarm*
 
+## swarm mode
+
+[Swarm mode](../swarm/index.md) refers to cluster management and orchestration
+features embedded in Docker Engine. When you initialize a new swarm (cluster) or
+join nodes to a swarm, the Docker Engine runs in swarm mode.
+
 ## tag
 
 A tag is a label applied to a Docker image in a [repository](#repository).
@@ -197,6 +246,18 @@ tags are how various images in a repository are distinguished from each other.
 
 *Note : This label is not related to the key=value labels set for docker daemon*
 
+## task
+
+A [task](../swarm/how-swarm-mode-works/services.md#tasks-and-scheduling) is the
+atomic unit of scheduling within a swarm. A task carries a Docker container and
+the commands to run inside the container. Manager nodes assign tasks to worker
+nodes according to the number of replicas set in the service scale.
+
+The diagram below illustrates the relationship of services to tasks and
+containers.
+
+![services diagram](../swarm/images/services-diagram.png)
+
 ## Toolbox
 
 Docker Toolbox is the installer for Mac and Windows users.
@@ -209,13 +270,13 @@ very lightweight and fast. Docker uses union file systems to provide the buildin
 blocks for containers.
 
 
-## Virtual Machine
+## virtual machine
 
-A Virtual Machine is a program that emulates a complete computer and imitates dedicated hardware.
+A virtual machine is a program that emulates a complete computer and imitates dedicated hardware.
 It shares physical hardware resources with other users but isolates the operating system. The
 end user has the same experience on a Virtual Machine as they would have on dedicated hardware.
 
-Compared to to containers, a Virtual Machine is heavier to run, provides more isolation,
+Compared to to containers, a virtual machine is heavier to run, provides more isolation,
 gets its own set of resources and does minimal sharing.
 
 *Also known as : VM*