Mastering Docker is a sought-after skill for backend software engineers. Docker will help you to build, package, and distribute applications.
Dockerized applications can run in various environments. This lowers the application downtime giving businesses a competitive edge. But Docker can be intimidating when you start learning it. Here are vital topics to learn to master Docker.
What Is Docker?
Docker is a software used to package applications into executable units called containers. Docker provides support to build, test, and deploy applications quickly.
When you use Docker, you interact with the Docker Engine. You can install Docker Engine on any operating system, includingWindows 10 and 11,macOS, orUbuntu/Linux systems. There are many tools and concepts you need to learn to use Docker effectively. Here are the most essential ones to get you started.
1. Docker Image
A Docker image is a lightweight blueprint used to create containers. It’s a template of instructions specifying the operating system, application code, and dependencies. You define instructions on how to build the image on a Dockerfile.
In the file, you indicate everything your application needs. Docker then auto-builds the image based on the instructions provided. you may find various images on Docker’s online registry, Docker Hub. Docker recommends using the official images for security purposes.
you’re able to also build images based on customized configurations. Images come in various sizes, operating systems, and languages. You can choose the one that best suits your application. For instance, you can learnhow to build a Docker image of a .NET web API.
2. Docker Container
Containers are units used to package an application into an executable unit. Containers include everything needed to run an application, including libraries, code, dependencies, and runtime.
Containers isolate applications into units allowing them to run consistently across various environments. Containers allow you to manage applications in development and production environments without encountering errors. There aremany use cases for containersthat you can explore.
Docker containers have details like the container ID, image, and base operating system. You can also see the runtime, status, and name of the container. To list all containers in your system, use the following command:
You will see details of all running containers:
You can also usedocker psto view all running containers. Anddocker container inspect [container ID]to view the contents of a container.
4. Dockerfile
A Dockerfile is a document that specifies instructions on how to build the Docker image. The file specifies the base image, the application code, and the files needed to create the image.
The file also includes the environment variables and the commands for image creation. you may create a Dockerfile like any other file. You must specify the instructions on the file using a syntax that Docker understands. Following is an example of a sample Dockerfile:
5. Docker Compose
Docker Compose is a tool for defining and running multi-container Docker applications. You configure all the services in a YAML file. A YAML file is a document where you specify the needed services for your application. you may then create and run all the services using a single command.
Docker Compose can run applications in various environments. These can be production, staging, development, or testing environments. Docker Compose simplifies the complex process of orchestrating multiple containers.
You can use Docker Compose to manage an application throughout its life cycle. This can include starting, stopping, and rebuilding services. You can also view the status of running services, stream log output, and run commands on a service.
With Docker Compose, you’re able to configure networks, manage volumes, and specify dependencies. You can also scale applications horizontally in production by specifying replica services.
Compose simplifies the deployment of complex applications to various environments. You can also use it to replicate the same environment in different systems.Learning how to use Docker Composecan increase your application’s efficiency.
Here is an example of a Docker Compose YAML file:
6. Docker Hub
Docker Hubis an online container registry for Docker. Being the largest container registry, it’s a collaboration tool for developers and open-source contributors. It is also an excellent marketplace for software vendors.
Docker Hub is a trusted resource for finding reliable virtualization software. You can create a repository and share over 100,000 images.
You canhost your applicationsand code on the platform. You can also collaborate on projects with other developers. Docker Hub has a free public option or paid private repos for specific authorized teams.
7. Docker Networking
Docker networking is a feature that allows containers to communicate with each other and external resources. Networks provide controlled and isolated communication between containers. These can be containers running on single or multiple hosts.
When you run a container on your machine, it’s not exposed to external networks. You use ports to expose the containers to external IP addresses, DNS services, route tables, and internet gateways.
Networking allows containers to operate in isolated network environments. The networks provide namespaces and IP addresses, reducing container conflict and enhancing security.
8. Docker Volumes
In Docker, volumes are a mechanism used to store persistent data. By design, containers are ephemeral. Meaning it’s easy to replace or destroy them with all their data. But, there are instances you would wish to retain the data. In such cases, you’re able to use Docker volumes to manage persistent data.
Volumes also have other uses, including allowing sharing of data between containers. They are easy to back up and migrate compared to other forms of storage. Additionally, you can manage volumes using Docker CLI or the API.
If you run a container without a volume, Docker automatically creates one. You can also create and manage volumes isolated from any containers. Use the following command to create a volume.
To see the volume you created, run the following command:
You can then attach the volumes to any container that you wish. You can read more about volumes on theDockerofficial documentation.
Other Docker Features
Docker is one of the best choices for container management and version control. If you learn Docker’s toolset, you may boost and streamline your development workflow.
Docker has many features that you’re able to use to manage your applications. After mastering the key features, you can explore other complex features like Docker Swarm that’s used to orchestrate complex applications.
