Docker Concepts

Category : Docker | Sub Category : Docker for Java Developers | By Prasad Bonam Last updated: 2022-02-06 14:20:23 Viewed : 491

 Docker Concepts

Docker simplifies software delivery of distributed applications in three ways:

Build

Provides tools you can use to create containerized applications. Developers package the application, its dependencies and infra‐ structure, as read-only templates. These are called the Docker image.

Ship

Allows you to share these applications in a secure and collabo‐ rative manner. Docker images are stored, shared, and managed in a Docker registry

Docker Hub is a publicly available registry. This is the default registry for all images

Run

The ability to deploy, manage, and scale these applications. Docker container is a runtime representation of an image. Con‐ tainers can be run, started, scaled, stopped, moved, and deleted

Docker architecture

Docker host

A machine, either physical or virtual, is identified to run the Docker Engine.

Configure Docker client

The Docker client binary is downloaded on a machine and con‐ figured to talk to this Docker Engine. For development pur‐ poses, the client and Docker Engine typically are located on the same machine. The Docker Engine could be on a different host in the network as well.

Client downloads or builds an image

The client can pull a prebuilt image from the preconfigured reg‐ istry using the pull command, create a new image using the build command, or run a container using the run command.

Docker host downloads the image from the registry

The Docker Engine checks to see if the image already exists on the host. If not, then it downloads the image from the registry. Multiple images can be downloaded from the registry and installed on the host. Each image would represent a different software component. For example, WildFly and Couchbase are downloaded in this case.

Client runs the container

The new container can be created using the run command, which runs the container using the image definition. Multiple  containers, either of the same image or different images, run on the Docker host.

Docker Images and Containers

Docker images are read-only templates from which Docker contain‐ ers are launched. Each image consists of a series of layers. Docker makes use of a union filesystem to combine these layers into a single image. Union filesystems allow files and directories of separate file‐ systems, known as branches, to be transparently overlaid, forming a single coherent filesystem.

Docker Engine

Docker Engine is the central piece of Docker. It is a lightweight run‐ time that builds and runs your Docker containers. The runtime con‐ sists of a daemon that communicates with the Docker client and execute commands to build, ship, and run containers.