Docker Image Guide: How to Delete Docker Images, Stop Containers, and Remove all Volumes

Docker has taken the software development world by storm since its initial release in 2013. As a full-stack developer, I‘ve seen firsthand how Docker has transformed the way we build, package, and deploy applications. Its popularity continues to grow, with adoption increasing across organizations of all sizes.

Consider these stats:

• Over 13 million developers worldwide use Docker
• 55% of professional developers use Docker in their work
• 87% of companies using containers leverage Docker
• Docker Hub has over 100,000 container images and 200+ billion image pulls to date

Source: Docker company statistics, 2021

As more developers adopt Docker, it‘s crucial to understand how to effectively manage Docker images, containers, and volumes. This guide provides a comprehensive overview of key Docker concepts and commands, along with expert tips and best practices to keep your Docker environment organized and efficient.

Docker Images vs. Containers

Before diving into management techniques, let‘s clarify the difference between Docker images and containers.

A Docker image is a read-only template that defines an application and its dependencies. It includes everything needed to run the application, such as code, libraries, and system tools. Images are built from a series of filesystem layers, each representing an instruction in the image‘s Dockerfile.

A Docker container is a runnable instance of an image. When you start a container, Docker adds a writable layer on top of the image layers, allowing the running container to modify its filesystem. Multiple containers can be started from the same image, each with its own unique writable layer.

In short:

• Images are the building blocks, containers are the running instances
• Images are read-only, containers have a writable layer
• One image can spawn multiple containers

Essential Docker Commands

Here‘s a quick reference table of essential Docker commands for managing images, containers, and volumes:

Command	Description
docker images	List all images
docker rmi <image>	Remove an image
docker pull <image>	Download an image
docker run <image>	Start a new container from an image
docker ps	List running containers
docker ps -a	List all containers (including stopped)
docker stop <container>	Stop a running container
docker rm <container>	Remove a stopped container
docker volume create <vol>	Create a new volume
docker volume ls	List all volumes
docker volume rm <vol>	Remove a volume

Refer to the official Docker CLI reference for the full list of commands and options.

Managing Docker Images

Listing and Removing Images

To see all images on your system, run:

docker images

Each image is identified by its repository name, tag, and a unique ID. The SIZE column shows the cumulative space taken up by the image‘s layers.

To remove an image:

docker rmi <repository>:<tag>

Or reference it by ID:

docker rmi <image-id>

If an image is referenced by multiple tags, you need to remove each tag reference. Using the image ID removes the underlying image and all its tags at once.

Tagging Images

Image tags let you version and categorize images. To add a new tag to an existing image:

docker tag <source-image>:<tag> <target-image>:<tag>

For example, to tag the redis image with a specific version:

docker tag redis:latest redis:6.2.1

The same image ID now has two tags pointing to it. This is useful for maintaining multiple versions of an image without duplicating the full image data.

Organizing Images with Repositories

As you work with more images, consider organizing them into repositories on a Docker registry like Docker Hub. Use a naming convention that includes your username or organization name, followed by the image name:

<username>/<image>:<tag>

For example:

mycompany/api:v1.2.0
mycompany/web:v2.0.5

Grouping related images under a common prefix makes them easier to manage and identify. It also avoids naming conflicts with official images on Docker Hub.

Pruning Unused Images

Regularly pruning unused images frees up disk space and keeps your local image cache tidy. Docker provides a prune command to remove dangling images (those not referenced by any container):

docker image prune

To remove all images not used by any container, add the -a flag:

docker image prune -a

Use this command judiciously, as it removes all unused images, not just dangling ones.

Working with Containers

Running and Stopping Containers

To run a container from an image:

docker run <image>:<tag>

This starts the container and runs its default command in the foreground. To start the container in detached mode (background), add the -d flag:

docker run -d <image>:<tag>

To stop a running container:

docker stop <container-id>

You can restart a stopped container using docker start.

Removing Containers

To remove a stopped container:

docker rm <container-id>

Use the -f flag to force-remove a running container:

docker rm -f <container-id>

Automatically Removing Containers

For containers you don‘t need to persist after they exit, use the --rm flag to automatically remove them:

docker run --rm <image>

This is handy for ephemeral containers like short-lived build or test environments.

Persisting Data with Volumes

By default, any data written by a container is lost when the container is removed. To persist data beyond the container‘s lifecycle, use Docker volumes.

Volume Types

Docker supports three main types of volumes:

1. Named volumes: Created and managed by Docker, stored in a special directory on the host filesystem. Use when you need to share data between containers or simply persist data without exposing it on the host.

2. Bind mounts: Mount a directory from the host into the container. Use when you need to share data between the host and containers, or between containers and the host.

3. tmpfs mounts: Temporary filesystem stored in the host‘s memory. Use for secrets or sensitive data you don‘t want written to disk. Not persisted when the container stops.

Creating and Mounting Volumes

To create a named volume:

docker volume create <vol-name>

To mount a volume into a container at startup, use the -v flag:

docker run -v <vol-name>:<path/in/container> <image>

For example, to persist a Redis container‘s data directory:

docker run -d -v redis-data:/data redis:6

This creates a volume named redis-data if it doesn‘t exist and mounts it to /data inside the container.

Sharing Volumes Between Containers

Named volumes can be shared between multiple containers. This is useful for applications that need to access a common dataset.

To share a volume, simply reference the same volume name when starting each container:

docker run -d -v shared-data:/data app1
docker run -d -v shared-data:/data app2

Now app1 and app2 can both read and write to the shared-data volume.

When to Use Named Volumes vs. Bind Mounts

In general, prefer using named volumes for most use cases. They offer better portability and are managed by Docker, making them safer to use.

Use bind mounts when you need to share data between the host and containers, or when you need to provide configuration files to containers. Be cautious with bind mounts, as they expose the host filesystem to the container.

Housekeeping and Disk Space

To keep your Docker environment lean and clean, periodically prune unused assets. Docker provides prune commands for removing stopped containers, unused images, and orphaned volumes:

• docker container prune: Remove all stopped containers
• docker image prune: Remove unused images (dangling images)
• docker image prune -a: Remove all unused images, not just dangling ones
• docker volume prune: Remove all unused volumes

For a full system prune, use:

docker system prune

This removes all stopped containers, unused networks, and dangling images. Add the -a flag to remove all unused images as well.

Pruning is a safe operation, but always double-check before removing assets in production environments.

Real-World Tips and Lessons Learned

As a seasoned developer, I‘ve picked up a few valuable lessons working with Docker:

1. Use descriptive tags for your images, including version numbers or git commit SHAs. This makes it easier to track and roll back changes.

2. Carefully consider what you include in your images. Aim for lightweight images that contain only the essentials. This reduces image size and improves performance.

3. Use multi-stage builds to keep your final production images lean. Build artifacts in one stage, then copy only the necessary files to the final stage.

4. Invest time in writing clear, well-organized Dockerfiles. They serve as documentation for your images and make them easier to maintain.

5. Don‘t run containers as root unless necessary. Create a dedicated user with the minimum required permissions.

6. Use Docker Compose for defining and running multi-container applications. It simplifies orchestration and makes your setup more portable.

Conclusion

We‘ve covered a lot of ground in this guide, from fundamental Docker concepts to practical tips for managing images, containers, and volumes. As you dive deeper into the world of Docker, keep these key points in mind:

• Images are the templates, containers are the running instances.
• Use descriptive tags and repositories to organize your images.
• Prefer named volumes for persisting data and sharing between containers.
• Use bind mounts sparingly and with caution.
• Regularly prune unused assets to free up disk space.
• Follow best practices for writing Dockerfiles and building images.

Docker is a powerful tool that can streamline your development and deployment workflows. By mastering the techniques outlined in this guide, you‘ll be well-equipped to create efficient, portable, and maintainable applications using Docker.

For further reading, consult the official Docker documentation, which provides in-depth coverage of all Docker features and commands. The Docker community is also a great resource, with active forums, blogs, and social media channels where developers share knowledge and collaborate on solving challenges.

Happy Dockerizing!