instruction: Explain What is Docker?
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  Docker is an open platform for developing, shipping, and running applications.
  Docker enables you to separate your applications from your infrastructure so
  you can deliver software quickly. With Docker, you can manage your infrastructure
  in the same ways you manage your applications. By taking advantage of Docker's
  methodologies for shipping, testing, and deploying code, you can
  significantly reduce the delay between writing code and running it in production.
  The Docker platform
  Docker provides the ability to package and run an application in a loosely isolated
  environment called a container. The isolation and security lets you run many
  containers simultaneously on a given host. Containers are lightweight and contain
  everything needed to run the application, so you don't need to rely on what's
  installed on the host. You can share containers while you work,
  and be sure that everyone you share with gets the same container that works in the
  same way.
  Docker provides tooling and a platform to manage the lifecycle of your containers:
  Develop your application and its supporting components using containers.
  The container becomes the unit for distributing and testing your application.
  When you're ready, deploy your application into your production environment,
  as a container or an orchestrated service. This works the same whether your
  production environment is a local data center, a cloud provider, or a hybrid
  of the two.
  What can I use Docker for?
  Fast, consistent delivery of your applications
  Docker streamlines the development lifecycle by allowing developers to work in
  standardized environments using local containers which provide your applications
  and services. Containers are great for continuous integration and continuous
  delivery (CI/CD) workflows.
  Consider the following example scenario:
  Your developers write code locally and share their work with their colleagues
  using Docker containers.
  They use Docker to push their applications into a test environment and run
  automated and manual tests.
  When developers find bugs, they can fix them in the development environment
  and redeploy them to the test environment for testing and validation.
  When testing is complete, getting the fix to the customer is as simple as
  pushing the updated image to the production environment.
  Responsive deployment and scaling
  Docker's container-based platform allows for highly portable workloads. Docker
  containers can run on a developer's local laptop, on physical or virtual
  machines in a data center, on cloud providers, or in a mixture of environments.
  Docker's portability and lightweight nature also make it easy to dynamically
  manage workloads, scaling up or tearing down applications and services as
  business needs dictate, in near real time.
  Running more workloads on the same hardware
  Docker is lightweight and fast. It provides a viable, cost-effective alternative
  to hypervisor-based virtual machines, so you can use more of your server
  capacity to achieve your business goals. Docker is perfect for high density
  environments and for small and medium deployments where you need to do more with
  fewer resources.
  Docker architecture
  Docker uses a client-server architecture. The Docker client talks to the
  Docker daemon, which does the heavy lifting of building, running, and
  distributing your Docker containers. The Docker client and daemon can
  run on the same system, or you can connect a Docker client to a remote Docker
  daemon. The Docker client and daemon communicate using a REST API, over UNIX
  sockets or a network interface. Another Docker client is Docker Compose,
  that lets you work with applications consisting of a set of containers.
  The Docker daemon
  The Docker daemon (
  dockerd
  ) listens for Docker API requests and manages Docker
  objects such as images, containers, networks, and volumes. A daemon can also
  communicate with other daemons to manage Docker services.
  The Docker client
  The Docker client (
  docker
  ) is the primary way that many Docker users interact
  with Docker. When you use commands such as
  docker run
  , the client sends these
  commands to
  dockerd
  , which carries them out. The
  docker
  command uses the
  Docker API. The Docker client can communicate with more than one daemon.
  Docker Desktop
  Docker Desktop is an easy-to-install application for your Mac, Windows or Linux environment that enables you to build and share containerized applications and microservices. Docker Desktop includes the Docker daemon (
  dockerd
  ), the Docker client (
  docker
  ), Docker Compose, Docker Content Trust, Kubernetes, and Credential Helper. For more information, see
  Docker Desktop
  Docker registries
  A Docker registry stores Docker images. Docker Hub is a public
  registry that anyone can use, and Docker looks for images on
  Docker Hub by default. You can even run your own private registry.
  When you use the
  docker pull
  docker run
  commands, Docker pulls the required images from your configured registry. When you use the
  docker push
  command, Docker pushes
  your image to your configured registry.
  Docker objects
  When you use Docker, you are creating and using images, containers, networks,
  volumes, plugins, and other objects. This section is a brief overview of some
  of those objects.
  Images
  An image is a read-only template with instructions for creating a Docker
  container. Often, an image is based on another image, with some additional
  customization. For example, you may build an image which is based on the
  ubuntu
  image, but installs the Apache web server and your application, as well as the
  configuration details needed to make your application run.
  You might create your own images or you might only use those created by others
  and published in a registry. To build your own image, you create a Dockerfile
  with a simple syntax for defining the steps needed to create the image and run
  it. Each instruction in a Dockerfile creates a layer in the image. When you
  change the Dockerfile and rebuild the image, only those layers which have
  changed are rebuilt. This is part of what makes images so lightweight, small,
  and fast, when compared to other virtualization technologies.
  Containers
  A container is a runnable instance of an image. You can create, start, stop,
  move, or delete a container using the Docker API or CLI. You can connect a
  container to one or more networks, attach storage to it, or even create a new
  image based on its current state.
  By default, a container is relatively well isolated from other containers and
  its host machine. You can control how isolated a container's network, storage,
  or other underlying subsystems are from other containers or from the host
  machine.
  A container is defined by its image as well as any configuration options you
  provide to it when you create or start it. When a container is removed, any changes to
  its state that aren't stored in persistent storage disappear.
  Example
  docker run
  command
  The following command runs an
  ubuntu
  container, attaches interactively to your
  local command-line session, and runs
  /bin/bash
  docker run -i -t ubuntu /bin/bash
  When you run this command, the following happens (assuming you are using
  the default registry configuration):
  If you don't have the
  ubuntu
  image locally, Docker pulls it from your
  configured registry, as though you had run
  docker pull ubuntu
  manually.
  Docker creates a new container, as though you had run a
  docker container create
  command manually.
  Docker allocates a read-write filesystem to the container, as its final
  layer. This allows a running container to create or modify files and
  directories in its local filesystem.
  Docker creates a network interface to connect the container to the default
  network, since you didn't specify any networking options. This includes
  assigning an IP address to the container. By default, containers can
  connect to external networks using the host machine's network connection.
  Docker starts the container and executes
  /bin/bash
  . Because the container
  is running interactively and attached to your terminal (due to the
  flags), you can provide input using your keyboard while Docker logs the output to
  your terminal.
  When you run
  exit
  to terminate the
  /bin/bash
  command, the container
  stops but isn't removed. You can start it again or remove it.
  The underlying technology
  Docker is written in the
  Go programming language
  and takes
  advantage of several features of the Linux kernel to deliver its functionality.
  Docker uses a technology called
  namespaces
  to provide the isolated workspace
  called the container. When you run a container, Docker creates a set of
  namespaces for that container.
  These namespaces provide a layer of isolation. Each aspect of a container runs
  in a separate namespace and its access is limited to that namespace.
  Next steps
  Install Docker
  Get started with Docker