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Troubleshooting the Docker KeyError 'ContainerConfig' on Ubuntu

Introduction​

When working with Docker, you might come across a KeyError: 'ContainerConfig' message after running docker-compose up. This error can be frustrating, but it usually points to a specific problem with how Docker is managing container configurations, especially concerning volumes.

This guide will walk you through why this error occurs and how to resolve it on an Ubuntu system. By following these steps, you'll be able to get your containers running smoothly again.

The Problem: What Causes the 'ContainerConfig' Error?​

The full error message often includes a traceback that looks something like this:

ERROR: for n8n_image_n8n_1  'ContainerConfig'

ERROR: for n8n  'ContainerConfig'
Traceback (most recent call last):
...
KeyError: 'ContainerConfig'

The key part of the error message is container.image_config['ContainerConfig'].get('Volumes'). This indicates that Docker is having trouble accessing the volume information associated with the container's image configuration. This can happen if the image or its associated volumes have become corrupted or are in an inconsistent state.

The Solution: A Step-by-Step Guide​

Here’s how to fix the KeyError: 'ContainerConfig' error.

Step 1: Stop and Remove Existing Containers​

The first step is to stop and remove any running containers associated with your docker-compose.yml file. This ensures that you are starting from a clean slate.

Open your terminal and run the following command in the same directory as your docker-compose.yml file:

sudo docker-compose down

Step 2: Remove Volumes and Images​

The error is often related to inconsistent or corrupted volumes and images. To fix this, you need to remove them completely. The --volumes flag removes anonymous volumes, and --rmi all removes all images used by the services defined in your docker-compose.yml.

Execute the following command:

sudo docker-compose down --volumes --rmi all

This command will:

  • Stop all running services.
  • Remove the containers, networks, and volumes.
  • Remove all Docker images used by the services.

Step 3: Rebuild and Start Your Containers​

Now that you have a clean environment, you can rebuild and restart your containers.

Run the up command with the --build flag to ensure that Docker rebuilds the images from scratch:

sudo docker-compose up --build

Your containers should now start without the KeyError: 'ContainerConfig' error.

Conclusion​

The KeyError: 'ContainerConfig' error in Docker can be a roadblock, but it's usually straightforward to fix. By completely removing the old containers, volumes, and images, you can clear out any corrupted data and start fresh. This guide has shown you how to resolve this issue on Ubuntu, allowing you to get back to developing and running your applications.

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