Understanding the Difference Between Docker Images and Containers

Introduction

In the world of Docker, understanding the disparity between images and containers is crucial. Docker images and containers are fundamental components of Docker technology, but they serve distinct purposes. Let’s delve deeper into each and clarify their disparities.

Docker Images

Docker images are the building blocks of Docker containers. They are lightweight, standalone, executable packages that include everything needed to run a piece of software, including the code, runtime, libraries, environment variables, and system tools. Docker images are immutable, meaning once created, they cannot be changed.

Docker Containers

Docker containers are instances of Docker images that can be executed and run on a host machine. They are lightweight, portable, and isolated environments that encapsulate an application along with its dependencies. Containers run as isolated processes on the host operating system, utilizing the resources allocated to them.

Key Differences Between Docker Images and Containers

Now that we have a basic understanding of Docker images and containers, let’s highlight their key differences:

1. Immutability: Docker images are immutable, meaning they cannot be changed once created. Containers, on the other hand, are mutable and can be modified during runtime.
2. Execution: Docker images are static, while containers are dynamic and can be started, stopped, and restarted as needed.
3. Storage: Docker images are stored in a Docker registry, such as Docker Hub, whereas containers are instantiated from these images and run on Docker hosts.

Code Examples

Let’s illustrate the concepts discussed above with some code examples:

Creating a Docker Image

# Dockerfile
FROM alpine:latest
WORKDIR /app
COPY . .
CMD ["./app"]

# Build the Docker image
docker build -t myapp .

Running a Docker Container

# Run a container from the previously built image
docker run -d --name mycontainer myapp

Modifying a Docker Container

# Access the container's shell
docker exec -it mycontainer /bin/sh

# Modify files or configurations within the container
echo "Updated content" > file.txt

# Exit the container shell
exit

Committing Changes to a Docker Image

# Commit changes made in the container to a new image
docker commit mycontainer myapp:v2

Conclusion

Understanding the difference between Docker images and containers is fundamental for effectively working with Docker technology. Images serve as immutable blueprints for containers, while containers provide the dynamic runtime environment for applications. With this knowledge, you are well-equipped to leverage Docker for building, deploying, and managing your applications efficiently.