Linux containers and docker

Use containers to Build, Share and Run your applications

Package Software into Standardized Units for Development, Shipment and Deployment

• Standard: Docker created the industry standard for containers, so they could be portable anywhere
• Lightweight: Containers share the machine’s OS system kernel and therefore do not require an OS per application, driving higher server efficiencies and reducing server and licensing costs
• Secure: Applications are safer in containers and Docker provides the strongest default isolation capabilities in the industry

Docker Containers Are Everywhere: Linux, Windows, Data center, Cloud, Serverless, etc.

Docker container technology was launched in 2013 as an open source Docker Engine. It leveraged existing computing concepts around containers and specifically in the Linux world, primitives known as cgroups and namespaces. Docker’s technology is unique because it focuses on the requirements of developers and systems operators to separate application dependencies from infrastructure. Success in the Linux world drove a partnership with Microsoft that brought Docker containers and its functionality to Windows Server. Technology available from Docker and its open source project, Moby has been leveraged by all major data center vendors and cloud providers. Many of these providers are leveraging Docker for their container-native IaaS offerings. Additionally, the leading open source serverless frameworks utilize Docker container technology.

Comparing Containers and Virtual Machines

Containers and virtual machines have similar resource isolation and allocation benefits, but function differently because containers virtualize the operating system instead of hardware. Containers are more portable and efficient.

CONTAINERS

Containers are an abstraction at the app layer that packages code and dependencies together. Multiple containers can run on the same machine and share the OS kernel with other containers, each running as isolated processes in user space. Containers take up less space than VMs (container images are typically tens of MBs in size), can handle more applications and require fewer VMs and Operating systems.

VIRTUAL MACHINES

Virtual machines (VMs) are an abstraction of physical hardware turning one server into many servers. The hypervisor allows multiple VMs to run on a single machine. Each VM includes a full copy of an operating system, the application, necessary binaries and libraries – taking up tens of GBs. VMs can also be slow to boot.

Containers and Virtual Machines Together

Containers and VMs used together provide a great deal of flexibility in deploying and managing app

Container Standards and Industry Leadership

The launch of Docker in 2013 jump started a revolution in application development – by democratizing software containers. Docker developed a Linux container technology – one that is portable, flexible and easy to deploy. Docker open sourced libcontainer and partnered with a worldwide community of contributors to further its development. In June 2015, Docker donated the container image specification and runtime code now known as runc, to the Open Container Initiative (OCI) to help establish standardization as the container ecosystem grows and matures.

Following this evolution, Docker continues to give back with the containerd project, which Docker donated to the Cloud Native Computing Foundation (CNCF) in 2017. containerd is an industry-standard container runtime that leverages runc and was created with an emphasis on simplicity, robustness and portability. containerd is the core container runtime of the Docker Engine.

Choose a plan that’s right for you

Docker isn’t just for personal projects. Discover the perfect plan to empower your team and streamline your workflow.

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Overview

Welcome! We’re excited that you want to learn Docker.

This guide contains step-by-step instructions on how to get started with Docker. Some of the things you’ll learn and do in this guide are:

• Build and run an image as a container.
• Share images using Docker Hub.
• Deploy Docker applications using multiple containers with a database.
• Run applications using Docker Compose.

Before you get to the hands on part of the guide, you should learn about containers and images.

What is a container?

Simply put, a container is a sandboxed process on your machine that is isolated from all other processes on the host machine. That isolation leverages kernel namespaces and cgroups, features that have been in Linux for a long time. Docker has worked to make these capabilities approachable and easy to use. To summarize, a container:

• Is a runnable instance of an image. You can create, start, stop, move, or delete a container using the DockerAPI or CLI.
• Can be run on local machines, virtual machines or deployed to the cloud.
• Is portable (can be run on any OS).
• Is isolated from other containers and runs its own software, binaries, and configurations.

What is a container image?

When running a container, it uses an isolated filesystem. This custom filesystem is provided by a container image. Since the image contains the container’s filesystem, it must contain everything needed to run an application — all dependencies, configurations, scripts, binaries, etc. The image also contains other configuration for the container, such as environment variables, a default command to run, and other metadata.

You’ll dive deeper into images later on in this guide, covering topics such as layering, best practices, and more.

Note

If you’re familiar with chroot , think of a container as an extended version of chroot . The filesystem is simply coming from the image. But, a container adds additional isolation not available when simply using chroot.

Next steps

In this section, you learned about containers and images.

In the next section, you’ll containerize your first application.

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How do I run a container?

Follow this guide to learn the basic steps of running a container from scratch. This guide uses a sample Node.js application, but it’s not necessary to know Node.js.

Step 1: Get the sample application

If you have git, you can clone the repository for the sample application. Otherwise, you can download the sample application. Choose one of the following options.

Clone with git

Use the following command in a terminal to clone the sample application repository.

$ git clone https://github.com/docker/welcome-to-docker 

Download

If you don’t have git, download the source and extract it.

Step 2: Explore the Dockerfile

To run your code in a container, the most fundamental thing you need is a Dockerfile. A Dockerfile describes what goes into a container. Open the sample application in your IDE and then open the Dockerfile to explore its contents. Note that this project already has a Dockerfile, but for your own projects you need to create a Dockerfile. A Dockerfile is simply a text file named Dockerfile with no file extension.

Step 3: Build your first image

An image is like a static version of a container. You always need an image to run a container. Once you have a Dockerfile in your repository, run the following docker build command in the project folder to create an image.

$ docker build -t welcome-to-docker . 

Building the image may take some time. After your image is built, you can view your image in the Images tab in Docker Desktop.

Step 4: Run your container

To run your image as a container, go to the Images tab, and then select Run in the Actions column of your image. When the Optional settings appear, specify the Host port number 8089 and then select Run.

Step 5: Verify that your container is running

You can use Docker Desktop to view and access running containers. Go to the Containers tab to view your container and select the link in the Port(s) column or go to http://localhost:8089 to verify that the application is running.

What’s next

In this guide, you built your own image. When running containers on Docker Desktop, you don’t need to build your own image from scratch. You can also run images created by others on Docker Hub.

Dive deeper

Language-specific guides

If you want to learn more about creating images for applications in other languages, check out the following language-specific guides:

Breaking down the docker build command

When you built the image, you used the docker build command. Here are what the different parts of the docker build command do:

• docker build : This command builds the image. It needs one argument, the source folder for the Dockerfile that needs to be built. In this case, it’s the Dockerfile in the current folder, . .
• -t welcome-to-docker : The -t flag tags the image with a unique name. In this case, welcome-to-docker .

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