Managing Docker Contexts to Prevent Image Disappearance and Permission Issues

Introduction

In the world of containerisation, Docker has become an integral tool for developers to manage and deploy applications seamlessly. However, occasional hiccups in the Docker environment can lead to perplexing issues, such as vanishing local Docker images and unexpected permission requirements. In this article, we'll delve into a recent experience that sheds light on this phenomenon and explore the solutions to mitigate such occurrences.

The Mysterious Disappearance

Imagine a scenario where you've just installed Docker Desktop, and suddenly, your locally built Docker images have vanished into thin air. Additionally, executing basic Docker commands prompts an unexpected request for sudo privileges. Without elevated permissions, an error message resembling the following surfaces:

"Cannot connect to the Docker daemon at unix:///home/xyz/.docker/desktop/docker.sock. Is the Docker daemon running?"

Perplexing as this may seem, the root cause of this anomaly lies in Docker's inherent architecture and its management of different contexts.

Docker Context: Unveiling the Culprit

Docker Desktop, upon initiation, crafts a dedicated context to serve as a target for the Docker Command-Line Interface (CLI). This context is set as the active one for the CLI's use. This seemingly innocuous process serves a vital purpose: it prevents conflicts with a local Docker Engine that could potentially be operational on the Linux host and utilizing the default context.

The purpose of this context isolation becomes apparent during shutdown. When Docker Desktop closes, it restores the previously employed context to ensure a smooth transition between different Docker environments.

Solving the Mystery: Unveiling the Solution

Now that we've dissected the cause, let's unravel the solution. The Docker website itself offers insights into this quandary, suggesting a course of action to restore normalcy. If you find yourself grappling with Docker images mysteriously disappearing and unexpected permission requirements, consider these steps:

One initial remedy is to add yourself to the 'docker' group using the following command:

1. User Group Addition:

sudo usermod -aG docker $USER

1. Context Exploration:

To comprehend the current context at play, utilize the command:

docker context list

1. Context Switching:

When you are not using docker desktop if you suspect that Docker Desktop might have altered your context, manually switch back to your original context using:

docker context use <context-name>