This guide explores various Docker run commands and options with examples and challenges to enhance your understanding and skills.
In this guide, we explore various Docker run commands and options, providing clear examples and practical challenges to solidify your understanding. By the end of this article, you’ll be well-equipped to execute and experiment with these commands.
Previously, we used the following command to run a Redis container:
docker run redis
By default, Docker pulls the image tagged as “latest” (currently corresponding to version 5.0.5). If you prefer to run a different version—say, version 4.0—you must specify the tag after a colon:
docker run redis:4.0
In this example, Docker retrieves Redis version 4.0. Remember, when no tag is indicated, Docker assumes “latest.” For a complete list of supported tags, refer to the image’s Docker Hub page, where both short and long tags are documented. Notably, version 5.0.5 is also identified by the “latest” tag.
Consider an application that asks the user for their name and then displays a welcome message. Running the application locally produces:
~/prompt-application$ ./app.shWelcome! Please enter your name: MumshadHello and Welcome Mumshad!
If you dockerize this application and run it without additional options, it won’t wait for input because Docker containers run in non-interactive mode by default:
docker run kodekloud/simple-prompt-dockerHello and Welcome !
Even specifying the -i flag (interactive mode) alone does not display the prompt, as the container isn’t attached to a terminal:
docker run -i kodekloud/simple-prompt-dockerMumshadHello and Welcome Mumshad!
For applications requiring user input, always combine the -i (interactive) and -t (pseudo terminal allocation) options:
Using both flags ensures that the application properly prompts for input and displays output as if running in a standard terminal:
docker run -it kodekloud/simple-prompt-dockerWelcome! Please enter your name: MumshadHello and Welcome Mumshad!
When running a containerized web application that listens on port 5000, the container’s internal IP (e.g., 172.17.0.2) is only accessible within the Docker host. To expose the application externally, you must map a free host port to the container’s port using the -p parameter.For instance, to route traffic from port 80 on your Docker host to port 5000 in the container, run:
docker run kodekloud/webapp* Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)docker run -p 80:5000 kodekloud/webapp
Now, users can access your web application via http://192.168.1.5:80 (assuming 192.168.1.5 is the Docker host IP). You can also run multiple instances of your application by mapping different host ports:
docker run -p 80:5000 kodekloud/webappdocker run -p 8000:5000 kodekloud/webappdocker run -p 8001:5000 kodekloud/webapp
For services like MySQL, you may choose to map its default port (3306) or an alternate host port (e.g., 8306) to allow multiple instances to operate concurrently without conflict.
By default, a MySQL container stores its data in /var/lib/mysql inside the container. However, since container filesystems are ephemeral, all data is lost when the container is removed. Consider the following example:
docker run mysqldocker stop mysqldocker rm mysql
All stored data is removed along with the container. To persist the data, mount a directory from your Docker host into the container. For example, create a directory /opt/datadir on your host and run:
docker run -v /opt/datadir:/var/lib/mysql mysql
This volume mapping ensures that the data in /opt/datadir remains intact even if the container is deleted.
To retrieve basic information about your running containers, use the docker ps command, which lists container names and IDs. For detailed information about a particular container, the docker inspect command provides comprehensive configuration details in JSON format. For example:
If you launch a container in detached mode using the -d flag, you may want to view its logs later. The docker logs command displays the standard output of a container. To view logs from a container named “blissful_hopper,” run:
docker logs blissful_hopper
An example output might be:
No command line argument or environment variable. Picking a Random Color = blue* Serving Flask app "app" (lazy loading)* Environment: productionWARNING: Do not use the development server in a production environment.Use a production WSGI server instead.* Debug mode: off* Running on http://0.0.0.0:8080/ (Press CTRL+C to quit)
This guide has provided a comprehensive overview of key Docker run commands, covering container image versions, interactive mode, port mapping, data persistence, container inspection, and log viewing. Practice these commands to reinforce your Docker skills and enhance your container management strategy.For further learning, refer to Docker Documentation and explore additional tutorials on containerization best practices.
