Day 19: Mastering Docker Commands and Concepts

This blog post aims to introduce Docker's most fundamental commands and concepts. DockerHub, Docker images, registries, and Docker container lifecycle will all be covered. Upon completion, readers will be equipped to effectively utilize Docker and perform practical tasks such as running an Nginx container.

What is DockerHub?

DockerHub is a cloud-based registry where Docker images are stored, shared, and distributed. It serves as a centralized platform for developers to find and use images for common applications, as well as to publish custom images.

Docker Images

A Docker Image is a lightweight, immutable file that contains all the dependencies, libraries, and configurations needed to run an application. Think of it as a stopped container, similar to a VM image.

Docker Registries

A Docker Registry is a repository for storing and managing Docker images. Registries can be cloud-based or self-hosted.

Cloud-Based Registries:

• Docker Hub
• Google Artifact Registry (GAR)
• Amazon Elastic Container Registry (ECR)
• Azure Container Registry (ACR)

In-House or Local Registries:

• Harbor
• Jfrog Artifactory
• DTR (Docker trusted Registry)

Task: Docker Nginx

In this task, we’ll run an Nginx container using Docker.

1. Pull the Nginx image:

2. Check the downloaded image:

3. Pull the Nginx image with specific version

4. Run the Nginx container

This command:

• Runs the container in detached mode (-d).
• Maps port 8080 on your host to port 80 in the container (-p).
• Names the container my-nginx.

5. List running containers

6. Stop and remove the container

Docker Commands

The following table lists essential Docker commands and their purposes

Docker Container Lifecycle

Docker containers go through a series of stages during their lifecycle. Understanding these stages, along with the actions and corresponding commands, is key to effectively managing containers.

Container Creation

A container is created from a Docker image but not yet running.

To create a container, use docker create command:

Container Running

A container is actively running and executing its assigned tasks.

Two Ways to Run a Container:

1. docker run
   1. The docker run command both creates and starts a container in a single step.
   2. If the container does not already exist, Docker will create one from the specified image, start it, and optionally execute a specified command.
   3. This command is ideal for initializing and running a new container.

2. docker start
   1. The docker start command starts an existing container that was previously stopped or created using docker create.
   2. It does not create a new container; it resumes the operation of an existing one.
   3. This is useful for reusing containers in recurring workflows.

Container Paused

A running container is temporarily paused, halting all processes without stopping it entirely.

To pause a container, use docker pause command:

To unpause a container, use docker unpause command:

Container Stopped

The container has been stopped, meaning all processes have terminated, but the container still exists.

To stop a container, use docker pause command:

Container Deleted

The container has been removed from the system, including its metadata and file system changes. This frees up Docker's storage and container resources. In order to stop the container, it must be stopped.

To remove a container, use docker rm command:

Wrapping Up

Docker commands and concepts form the backbone of container management. Achieving mastery of the lifecycle, registries, and essential commands is a major accomplishment.

In the next blog, we’ll explore the Docker logs command, diving into how to monitor and troubleshoot container activities effectively.

Happy New Year, fellow DevOps engineers! 🎆🎉❤️