Linux | Docker on Linux

Introduction

Docker is a lite-weight container in operating systems. Different from VM(virtual machine), docker is good at its weight and usage. In this article, I will conclude how I install a docker in Linux Ubuntu platform. Imgur Docker will share kernal with dominate operating system, it doesn’t requires hypervisor(my understanding is adapter) between operation system and docker container.

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Docker Image

Docker image is a special file system. It will provide the environment for running a docker container, including application, library, resource and configurations. Docker is like a class, it defines the structure and its related parameters.

Docker Container

Docker container is an instance created with the definition of docker image.

Docker Repository

Docker Repository is a platform to save docker images. Its function is really like github.

Development on Docker

Imgur

Docker Installation

Install docker application.
```
 sudo apt install docker.io
```
Check docker installation
```
 sudo docker info
```

Add current user to docker group

 sudo groupadd docker # if docker group doesn't exist, create a docker group.
 sudo gpasswd -a ${USER} docker # Add current user to docker group.

Run/Stop docker

Docker application will run as a deamon thread.

 sudo systemctl start docker
 sudo systemctl enable docker

Stop/restart docker.

 sudo systemctl stop docker
 sudo systemctl restart docker

Images

Check existing images on current docker
```
 sudo docker images
```
Pull a docker image from dockerhub, here I pulled a docker for spring cloud
```
 docker pull springcloudservices/spring-cloud-base
```
Search docker images
```
 docker search (image keyword)
```

Run one image

 # Check the name of that image
 docker ps -a
 # Create a container for a image.
 docker run -itd -p 5000:5000 (image id)
 # Enter the container
 docker attach 199c8075258c

Exit the container
```
 exit
```

Dockerfile

Dockerfile is a file to customize our own docker image from another docker image. 1. FROM: It is difficult to create a docker from nothing, so FROM is way to import an existing image and customize our own image based on that. 2. RUN: Shell commands are appended to RUN. We connected all the commands with symbol &&. We want to connect all commands by && so we don’t have to create different levels. 3. ARG: ARG is the short of ARGUMENTS. 4. ENV: Set up global environment.