--- title: Docker Context description: Learn about Docker Context keywords: engine, context, 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 ` to easily switch between them. For information on using Docker Context to deploy your apps to the cloud, see [Deploying Docker containers on Azure](aci-integration.md) and [Deploying Docker containers on ECS](ecs-integration.md). ## Prerequisites 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 through 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`). It 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 can 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 `. 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. You can also set the current context using the `DOCKER_CONTEXT` environment variable. This overrides 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_. You can export and import these 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 must have the Docker client installed. ``` $ docker context import docker-test docker-test.dockercontext docker-test Successfully imported context "docker-test" ``` You can verify that the context was imported with `docker context ls`. The format of the import command is `docker context import `. Now, let's look at exporting just the Kubernetes parts of a context. ### Exporting a Kubernetes context You can export a Kubernetes context only if the context you are exporting has a Kubernetes endpoint configured. You cannot import a Kubernetes context 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: 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 ``` You can merge this 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" ```