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Adding Docker Context customer beta2 user guide 

Signed-off-by: Nigel Poulton <nigelpoulton@hotmail.com>
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Nigel Poulton 2019-04-24 10:47:11 +00:00 committed by Maria Bermudez
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@ -3358,6 +3358,10 @@ manuals:
title: Sample apps with Compose
- path: /release-notes/docker-compose/
title: Docker Compose release notes
- sectiontitle: Docker Context
section:
- path: /engine/context/working-with-contexts/
title: Working with Docker Contexts
- sectiontitle: Docker Desktop for Mac
section:
- path: /docker-for-mac/

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---
title: Working with Contexts
description: Learn about Docker Contexts
keywords: engine, contexts, cli, kubernetes
---
## Introduction
This guide shows how _contexts_ make it easy for a **single Docker CLI** to manage multiple Swarm clusters, multiple Kubernetes clusters, and multiple individual Docker nodes.
A single Docker CLI can have multiple contexts. Each context contains all of the endpoint and security information required to manage a different cluster or node. The `docker context` command makes it easy to configure these contexts and switch between them.
As an example, a single Docker client on your company laptop might be configured with two contexts; **dev-k8s** and **prod-swarm**. **dev-k8s** contains the endpoint data and security credentials to configure and manage a Kubernetes cluster in a development environment. **prod-swarm** contains everything required to manage a Swarm cluster in a production environment. Once these contexts are configured, you can use the top-level `docker context use <context-name>` to easily switch between them.
## Pre-requisites
To follow the examples in this guide, you'll need:
- A Docker client that supports the top-level `context` command
Run `docker context` to verify that your Docker client supports contexts.
You will also need one of the following:
- Docker Swarm cluster
- Single-engine Docker node
- Kubernetes cluster
## The anatomy of a context
A context is a combination of several properties. These include:
- Name
- Endpoint configuration
- TLS info
- Orchestrator
The easiest way to see what a context looks like is to view the **default** context.
```
$ docker context ls
NAME DESCRIPTION DOCKER ENDPOINT KUBERNETES ENDPOINT ORCHESTRATOR
default * Current... unix:///var/run/docker.sock swarm
```
This shows a single context called "default". It's configured to talk to a Swarm cluster via the local `/var/run/docker.sock` Unix socket. It has no Kubernetes endpoint configured.
The asterisk in the `NAME` column indicates that this is the active context. This means all `docker` commands will be executed against the "default" context unless overridden with environment variables such as `DOCKER_HOST` and `DOCKER_CONTEXT`, or on the command-line with the `--context` and `--host` flags.
Dig a bit deeper with `docker context inspect`. In this example, we're inspecting the context called `default`.
```
$ docker context inspect default
[
{
"Name": "default",
"Metadata": {
"StackOrchestrator": "swarm"
},
"Endpoints": {
"docker": {
"Host": "unix:///var/run/docker.sock",
"SkipTLSVerify": false
}
},
"TLSMaterial": {},
"Storage": {
"MetadataPath": "\u003cIN MEMORY\u003e",
"TLSPath": "\u003cIN MEMORY\u003e"
}
}
]
```
This context is using "swarm" as the orchestrator (`metadata.stackOrchestrator`), is configured to talk to an endpoint exposed on a local Unix socket at `/var/run/docker.sock` (`Endpoints.docker.Host`), and requires TLS verification (`Endpoints.docker.SkipTLSVerify`).
### Create a new context
You create new contexts with the `docker context create` command.
The following example creates a new context called "docker-test" and specifies the following:
- Default orchestrator = Swarm
- Issue commands to the local Unix socket `/var/run/docker.sock`
```
$ docker context create docker-test \
--default-stack-orchestrator=swarm \
--docker host=unix:///var/run/docker.sock
Successfully created context "docker-test"
```
The new context is stored in a `meta.json` file below `~/.docker/contexts/`. Each new context you create gets its own `meta.json` stored in a dedicated sub-directory of `~/.docker/contexts/`.
> **Note:** The default context behaves differently than manually created contexts. It does not have a meta.json configuration file, and it dynamically updates based on the current configuration. For example, if you switch your current Kubernetes config using `kubectl config use-context`, the default Docker context will dynamically update itself to the new Kubernetes endpoint.
You can view the new context with `docker context ls` and `docker context inspect <context-name>`.
The following can be used to create a config with Kubernetes as the default orchestrator using the existing kubeconfig stored in `/home/ubuntu/.kube/config`. For this to work, you will need a valid kubeconfig file in `/home/ubuntu/.kube/config`. If your kubeconfig has more than one context, the current context (`kubectl config current-context`) will be used.
```
$ docker context create k8s-test \
--default-stack-orchestrator=kubernetes \
--kubernetes config-file=/home/ubuntu/.kube/config \
--docker host=unix:///var/run/docker.sock
Successfully created context "k8s-test"
```
You can view all contexts on the system with `docker context ls`.
```
$ docker context ls
NAME DESCRIPTION DOCKER ENDPOINT KUBERNETES ENDPOINT ORCHESTRATOR
default * Current unix:///var/run/docker.sock https://35.226.99.100 (default) swarm
k8s-test unix:///var/run/docker.sock https://35.226.99.100 (default) kubernetes
docker-test unix:///var/run/docker.sock swarm
```
The current context is indicated with an asterisk ("\*").
## Use a different context
You can use `docker context use` to quickly switch between contexts.
The following command will switch the `docker` CLI to use the "k8s-test" context.
```
$ docker context use k8s-test
k8s-test
Current context is now "k8s-test"
```
Verify the operation by listing all contexts and ensuring the asterisk ("\*") is against the "k8s-test" context.
```
$ docker context ls
NAME DESCRIPTION DOCKER ENDPOINT KUBERNETES ENDPOINT ORCHESTRATOR
default Current DOCKER_HOST based configuration unix:///var/run/docker.sock https://35.226.99.100 (default) swarm
docker-test unix:///var/run/docker.sock swarm
k8s-test * unix:///var/run/docker.sock https://35.226.99.100 (default) kubernetes
```
`docker` commands will now target endpoints defined in the "k8s-test" context.
It is also possible to set the current context using the `DOCKER_CONTEXT` environment variable. This will override the context set with `docker context use`.
Use the appropriate command below to set the context to `docker-test` using an environment variable.
Windows PowerShell:
```
> $Env:DOCKER_CONTEXT=docker-test
```
Linux:
```
$ export DOCKER_CONTEXT=docker-test
```
Run a `docker context ls` to verify that the "docker-test" context is now the active context.
You can also use the global `--context` flag to override the context specified by the `DOCKER_CONTEXT` environment variable. For example, the following will send the command to a context called "production".
```
$ docker --context production container ls
```
## Exporting and importing Docker contexts
The `docker context` command makes it easy to export and import contexts on different machines with the Docker client installed.
You can use the `docker context export` command to export an existing context to a file. This file can later be imported on another machine that has the `docker` client installed.
By default, contexts will be exported as a _native Docker contexts_. These can be exported and imported using the `docker context` command. If the context you are exporting includes a Kubernetes endpoint, the Kubernetes part of the context will be included in the `export` and `import` operations.
There is also an option to export just the Kubernetes part of a context. This will produce a native kubeconfig file that can be manually merged with an existing `~/.kube/config` file on another host that has `kubectl` installed. You cannot export just the Kubernetes portion of a context and then import it with `docker context import`. The only way to import the exported Kubernetes config is to manually merge it into an existing kubeconfig file.
Let's look at exporting and importing a native Docker context.
### Exporting and importing a native Docker context
The following example exports an existing context called "docker-test". It will be written to a file called `docker-test.dockercontext`.
```
$ docker context export docker-test
Written file "docker-test.dockercontext"
```
Check the contents of the export file.
```
$ cat docker-test.dockercontext
meta.json0000644000000000000000000000022300000000000011023 0ustar0000000000000000{"Name":"docker-test","Metadata":{"StackOrchestrator":"swarm"},"Endpoints":{"docker":{"Host":"unix:///var/run/docker.sock","SkipTLSVerify":false}}}tls0000700000000000000000000000000000000000000007716 5ustar0000000000000000
```
This file can be imported on another host using `docker context import`. The target host will need to have the Docker client installed.
```
$ docker context import docker-test docker-test.dockercontext
docker-test
Successfully imported context "docker-test"
```
You can verify the context was imported with `docker context ls`.
The format of the import command is `docker context import <context-name> <context-file>`.
Now let's look at exporting just the Kubernetes parts of a context.
### Exporting a Kubernetes context
This operation will only work if the context you are exporting has a Kubernetes endpoint configured. You will also not be able to import it using `docker context import`.
These steps will use the `--kubeconfig` flag to export **only** the Kubernetes elements of the existing `k8s-test` context to a file called "k8s-test.kubeconfig". The `cat` command will then show that it's exported as a valid kubeconfig file.
```
$ docker context export k8s-test --kubeconfig
Written file "k8s-test.kubeconfig"
```
Verify that the exported file contains a valid kubectl config.
```
$ cat k8s-test.kubeconfig
apiVersion: v1
clusters:
- cluster:
certificate-authority-data:
<Snip>
server: https://35.226.99.100
name: cluster
contexts:
- context:
cluster: cluster
namespace: default
user: authInfo
name: context
current-context: context
kind: Config
preferences: {}
users:
- name: authInfo
user:
auth-provider:
config:
cmd-args: config config-helper --format=json
cmd-path: /snap/google-cloud-sdk/77/bin/gcloud
expiry-key: '{.credential.token_expiry}'
token-key: '{.credential.access_token}'
name: gcp
```
This can be merged with an existing `~/.kube/config` file on another machine.
## Updating a context
You can use `docker context update` to update fields in an existing context.
The following example updates the "Description" field in the existing `k8s-test` context.
```
$ docker context update k8s-test --description "Test Kubernetes cluster"
k8s-test
Successfully updated context "k8s-test"
```