Docker: Advanced context usages

How to use Docker contexts in your scripts

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Working with Docker context use commands is excellent for manually executing commands. However, when using scripts, there are more suitable alternative methods that simplify the process. Instead of directly invoking the command, you can set the desired context using the DOCKER_CONTEXT environment variable. This approach integrates seamlessly into script workflows and maintains configuration clarity.

In the examples provided, replace <XXXXXX>.stackhero-network.com with your specific Docker instance domain (<XXXXXX>.stackhero-network.com).

Managing Docker contexts in bash scripts

Here is an example of how to set the Docker context within a bash script:

#!/bin/bash
set -e

DOCKER_CONTEXT=<XXXXXX>.stackhero-network.com

echo "IP from Docker for Stackhero instance:"
docker run --rm alpine wget -q -O - ifconfig.me

By setting the DOCKER_CONTEXT environment variable, you can conveniently manage the active context directly in your scripts.

Externalising configuration with a .env file

To avoid hardcoding the DOCKER_CONTEXT, you can load its value from a .env file. This method keeps environment settings organised and facilitates adjustments:

#!/bin/bash
set -e

source .env

echo "IP from Docker for Stackhero instance:"
docker run --rm alpine wget -q -O - ifconfig.me

Create a .env file with the following contents:

DOCKER_CONTEXT=<XXXXXX>.stackhero-network.com

Utilising Docker contexts in Makefiles

You can also set the DOCKER_CONTEXT variable in a Makefile. Here is an example of exporting the variable and executing a Docker container:

# Makefile
export DOCKER_CONTEXT=<XXXXXX>.stackhero-network.com

getIp:
	docker run --rm alpine wget -q -O - ifconfig.me

After creating the Makefile, invoke the command using:

make getIp

If you encounter the error Makefile: *** missing separator. Stop., ensure the docker run [...] line starts with a TAB character, not spaces.

Leveraging .env files in Makefiles

You can further simplify configuration by including a .env file in your Makefile. This approach ensures centralised management of your environment settings:

# Makefile
include .env
export

getIp:
	docker run --rm alpine wget -q -O - ifconfig.me

Create a .env file with this content:

DOCKER_CONTEXT=<XXXXXX>.stackhero-network.com

Then execute the command:

make getIp

If you encounter the error Makefile: *** missing separator. Stop., verify that the docker run [...] line begins with a TAB character rather than spaces.

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