and `user` (UID mapping). For more information about namespaces, see [Docker run reference](/engine/reference/run/) and [Isolate containers with a user namespace](/engine/security/userns-remap/).
node: |
A [node](/engine/swarm/how-swarm-mode-works/nodes/) is a physical or virtual
machine running an instance of the Docker Engine in [swarm mode](#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
for docker containers in a cluster.
overlay storage driver: |
OverlayFS is a [filesystem](#filesystem) service for Linux which implements a
[union mount](http://en.wikipedia.org/wiki/Union_mount) for other file systems.
It is supported by the Docker daemon as a storage driver.
parent image: |
An image's **parent image** is the image designated in the `FROM` directive
in the image's Dockerfile. All subsequent commands are based on this parent
image. A Dockerfile with the `FROM scratch` directive uses no parent image, and creates
a **base image**.
persistent storage: |
Persistent storage or volume storage provides a way for a user to add a
persistent layer to the running container's file system. This persistent layer
could live on the container host or an external device. The lifecycle of this
persistent layer is not connected to the lifecycle of the container, allowing
a user to retain state.
registry: |
A Registry is a hosted service containing [repositories](#repository) of [images](#image)
which responds to the Registry API.
The default registry can be accessed using a browser at [Docker Hub](#docker hub)
or using the `docker search` command.
repository: |
A repository is a set of Docker images. A repository can be shared by pushing it
to a [registry](#registry) server. The different images in the repository can be
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/).
SSH: |
SSH (secure shell) is a secure protocol for accessing remote machines and applications.
It provides authentication and encrypts data communication over insecure networks such
as the Internet. SSH uses public/private key pairs to authenticate logins.
service: |
A [service](/engine/swarm/how-swarm-mode-works/services/) 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](/engine/swarm/networking/#use-swarm-mode-service-discovery) 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](/engine/swarm/) is a cluster of one or more Docker Engines running in [swarm mode](#swarm_mode).
Docker Swarm: |
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](/engine/swarm/) 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).
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](/engine/swarm/how-swarm-mode-works/services/#/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