In this section, we will delve into the core functionality of Docker: running containers. Containers are the runtime instances of Docker images, and understanding how to run and manage them is crucial for any Docker user.

1. Docker Container: A lightweight, standalone, and executable package that includes everything needed to run a piece of software, including the code, runtime, libraries, and settings.
2. Docker Image: A read-only template used to create containers. Images are built from a series of layers.
3. Container Lifecycle: The stages a container goes through from creation to deletion.

The docker run command is used to create and start a container from a specified image.

Syntax:

Example:

Explanation:

• hello-world is the name of the Docker image.
• This command will download the hello-world image (if not already available locally) and run it, displaying a welcome message.

To run a container in the background (detached mode), use the -d option.

Example:

Explanation:

• -d runs the container in detached mode.
• nginx is the name of the Docker image.

You can assign a name to your container using the --name option.

Example:

Explanation:

• --name my-nginx assigns the name my-nginx to the container.

To map a port on the host to a port on the container, use the -p option.

Example:

Explanation:

• -p 8080:80 maps port 8080 on the host to port 80 on the container.

You can pass environment variables to a container using the -e option.

Example:

Explanation:

• -e MY_ENV_VAR=value sets the environment variable MY_ENV_VAR to value inside the container.

Let's run a simple web server using the nginx image.

Step-by-Step:

1. Pull the Nginx Image:

   docker pull nginx
   

2. Run the Nginx Container:

   docker run -d -p 8080:80 --name my-nginx nginx
   

3. Verify the Container is Running:

   docker ps
   

   Output:

   CONTAINER ID   IMAGE     COMMAND                  CREATED         STATUS         PORTS                  NAMES
   abc123def456   nginx     "/docker-entrypoint.…"   5 seconds ago   Up 4 seconds   0.0.0.0:8080->80/tcp   my-nginx
   

4. Access the Web Server: Open a web browser and navigate to http://localhost:8080. You should see the Nginx welcome page.

• Forgetting to Map Ports: Ensure you use the -p option to map the necessary ports, or your service won't be accessible from the host.
• Not Using Detached Mode: If you don't use -d, your terminal will be attached to the container's process, which might not be desirable for long-running services.
• Naming Containers: Use meaningful names for your containers to make management easier.

Task: Run a container using the alpine image and execute the echo "Hello, Docker!" command.

Solution:

Task: Run a container using the httpd image (Apache HTTP Server) and map port 8080 on the host to port 80 on the container.

Solution:

Task: Run a container using the alpine image and set an environment variable MY_VAR to Docker.

Solution:

In this section, we covered the basics of running Docker containers, including essential commands and options. You should now be able to run containers, map ports, set environment variables, and manage container names. In the next section, we will explore the container lifecycle and how to manage containers effectively.