In this article, we will explore the process of running a Docker image and the underlying steps that take place in the background. We'll cover the commands involved and explain each step in detail. So let's dive in!

Running the Docker Image: Basic Commands

To run a Docker image, we use the following command:

docker container run --publish 8080:80 --name some_container_name --detach image_name

Here we have a specific example:

docker container run --detach --publish 3306:3306 --env MYSQL_RANDOM_ROOT_PASSWORD=yes --name mysql_server3 mysql

• docker container run: This command is used to run a Docker container based on a specified image.

• --detach: This flag runs the container in the background (detached mode), allowing you to continue using the command prompt.

• --publish 3306:3306: This flag maps the host machine's port 3306 to the container's port 3306. It enables communication with the MySQL server running inside the container.

• --env MYSQL_RANDOM_ROOT_PASSWORD=yes: This flag sets an environment variable within the container. In this case, it sets MYSQL_RANDOM_ROOT_PASSWORD to "yes". This environment variable instructs MySQL to generate a random password for the root user during container initialization.

• --name mysql_server3: This flag assigns a name to the container. In this case, the container will be named "mysql_server3".

• mysql: This parameter specifies the Docker image to use for creating the container. In this example, it's the official MySQL image from Docker Hub.

Overall, this Docker command creates a container named "mysql_server3" based on the MySQL image. The container runs in the background, maps the host's port 3306 to the container's port 3306 for MySQL connectivity, and sets the environment variable MYSQL_RANDOM_ROOT_PASSWORD to "yes" for generating a random root password.

Please note that executing this command assumes you have the mysql Docker image pulled to your local machine. If the image is not available locally, Docker will automatically fetch it from the remote Docker repository (by default, Docker Hub) before creating the container.

What happens in the background?

Let's break down what happens behind the scenes when a user executes this command:

1. Docker searches for the image locally: Docker first checks if the specified image is available locally on the host machine. If it finds the image, it proceeds to step 4.

2. If the image is not found locally: In case the image is not present locally, Docker searches for it in a remote Docker repository. By default, the primary remote repository is Docker Hub. Docker pulls the image from the repository to the host machine.

3. Downloading the image: Once Docker locates the image in the remote repository, it proceeds to download the image onto the host machine. This step ensures that the required image is available for creating the container.

4. Creating a new container: Docker creates a new container based on the downloaded or local image. The container serves as an isolated and lightweight runtime environment that encapsulates the application and its dependencies.

5. Assigning a private IP: Inside the Docker container, a private IP address is assigned on a private network. This private network allows communication between containers running on the same host machine.

6. Port mapping: Docker opens up port 8080 on the host machine and forwards incoming traffic to port 80 within the container. This mapping enables external access to the containerized application via the specified port.

7. Starting the container: Finally, Docker starts the container, executing the command specified in the Docker image's Dockerfile. This command defines the initial actions to be performed when the container starts running.

By following these steps, Docker efficiently handles the process of running a containerized application based on the provided image.

Conslusions

In this article, we have explored the process of running Docker images and have gained insight into the background operations that occur during execution. We have examined the essential commands involved and provided a detailed explanation of each step.

Understanding these fundamental concepts and steps is crucial for effectively working with Docker containers. By mastering these techniques, you can harness the full power of Docker and leverage its benefits for your application development and deployment processes.

We hope this article has shed light on the intricacies of running Docker images and has provided you with a clearer understanding of the underlying processes. Stay tuned for more Docker-related content and further explore the vast capabilities of containerization technology.