How to Use the Command 'docker context' (with examples)

The docker context command is a powerful tool for managing multiple Docker environments seamlessly. By employing contexts, users can easily switch between different Docker servers, whether they’re hosted locally or remotely. This feature simplifies container management by eliminating the need to repeatedly update environment variables or reconfigure the Docker client settings. As a powerful utility in Docker’s command-line interface, it is particularly useful in scenarios involving development, testing, and production environments.

Use Case 1: Creating a Context Using a Specific Docker Endpoint

Code:

docker context create my_context --docker "host=tcp://remote-host:2375"

Motivation:

In a world where cloud computing and remote server management are ever-prevalent, developers often need to manage Docker containers on remote hosts. Creating a context that connects directly to a remote Docker daemon streamlines operations without needing intricate SSH tunneling or other complex setup procedures. This example is especially useful when you need to perform remote container operations but want to avoid the hassle of constantly updating your Docker endpoint settings.

Explanation:

• docker context create: This part of the command initializes the process of creating a new context.
• my_context: This is the name you are assigning to your new context. It acts as a label for easy reference when switching between contexts.
• --docker: This option specifies that the following string is a definition for the Docker endpoint.
• "host=tcp://remote-host:2375": This argument sets the Docker endpoint to communicate with. It specifies that the host is available at tcp://remote-host:2375, where remote-host should be substituted with the actual domain or IP address of your target Docker server, and 2375 is the typical port used for Docker TCP communication without TLS.

Example Output:

Successfully created context "my_context"

Use Case 2: Creating a Context Based on the DOCKER_HOST Environment Variable

Code:

docker context create my_context

Motivation:

When managing Docker environments, it is common to have the DOCKER_HOST environment variable set to define the Docker host’s location. This use case is particularly beneficial for developers who frequently switch between local development environments and remote servers without wanting to define endpoint addresses manually each time.

Explanation:

• docker context create: Initiates the creation of a new Docker context.
• my_context: The specified name of the context, easy to reference and use in subsequent operations.

In this scenario, since no Docker endpoint is specified with the --docker flag, Docker will use the value of the DOCKER_HOST environment variable to define the endpoint for this context. This variable typically holds a URL or IP address with the format similar to tcp://hostname:2375.

Example Output:

Using default context's Docker endpoint: tcp://hostname:2375
Successfully created context "my_context"

Use Case 3: Switching to a Context

Code:

docker context use my_context

Motivation:

Switching contexts is akin to selecting a profile within a configuration. It allows you to effortlessly redirect your Docker CLI operations to the predefined host environments without digging through system settings or configuration files. This procedure is invaluable in agile environments where operations may need to pivot quickly between testing, staging, and production.

Explanation:

• docker context use: This command switches the current context to the one specified following this phrase.
• my_context: Name of the context you wish to switch to. Instructs Docker to use the Docker endpoint and settings associated with my_context for subsequent commands.

Example Output:

Current context is now "my_context"

Use Case 4: Listing All Contexts

Code:

docker context ls

Motivation:

As the number of managed Docker environments grows, it’s essential to have an overview of all available contexts. The command for listing contexts provides this overview, enabling you to quickly identify existing contexts, check which one is active, and assess if any configurations need updating. This visibility is critical in ensuring proper and efficient Docker environment management.

Explanation:

• docker context ls: This command is used to display a list of all contexts available in the Docker system. It provides a detailed view of each context’s name, type, and endpoint address.

Example Output:

NAME        DESCRIPTION                               DEFAULT   DOCKER ENDPOINT
default     Current DOCKER_HOST based configuration   *         unix:///var/run/docker.sock
my_context                                            -         tcp://remote-host:2375

Conclusion:

The docker context command is an indispensable tool for managing multiple Docker environments efficiently. By creating, switching, and listing contexts, developers and system administrators can significantly streamline their workflow, minimizing time spent on environment configuration and maximizing productivity. Whether switching between local and remote Docker hosts or customizing environments for different stages of development, the docker context command goes a long way in simplifying these processes with its powerful capabilities.