Basics of the Container Engine

The container engine is an open source engine which allows you to create a lightweight, portable, and self-sufficient container for any application.

Preparations Before Installation

Before installing the container engine, you should understand the basic knowledge of the container engine. For details, see Docker Documentation.

Selecting an Edition of Container Engine

The container engine is compatible with almost all operating systems. Select an edition that best suits your needs. If you are not sure which edition to use, see https://docs.docker.com/engine/install/.

It is advised to install container engine 1.11.2 or later because earlier versions do not support image push to SWR.
If the container engine client is in a private network, bind an elastic IP address (EIP) to the client. This EIP will allow the client to download container engine installation packages from the website.

Installing the Container Engine

You can select either of the following installation procedures based on your OS.

Linux OS

EulerOS

Linux OS
Run the following commands to quickly install the latest edition. To install a specific edition, see Docker Engine installation overview.
```
curl -fsSL get.docker.com -o get-docker.sh
sh get-docker.sh
sudo systemctl daemon-reload
sudo systemctl restart docker
```
EulerOS
The procedure of installing the container engine in EulerOS is as follows:
1. Log in to ECS where you want to install the container engine.
2. Configure a yum repository.
  If you have not configured a yum repository on the host, configure one. For details, see How Can I Use an Automated Tool to Configure a Huawei Cloud Image Source (x86_64 and Arm)? If you have configured one, skip this step.
3. Install and run the container engine.
  1. Run the following command to obtain the docker-engine package from the yum repository.
    yum search docker-engine
  2. Run the yum install -y command to install the docker-engine package obtained in the previous step. The following is an example in the x86 architecture:
    yum install docker-engine.x86_64 -y
  3. Set the container engine to start at system startup.
    systemctl enable docker
  4. Start the container engine.
    systemctl start docker
4. Check the installation result.
  docker --version
  
  If information similar to the following is displayed, the container engine is successfully installed:
```
Docker version 18.09.0, build 384e3e9
```

Building a Container Image

This section walks you through the steps of using a Dockerfile to build a container image for a simple web application. Dockerfile is a text file that contains all the instructions a user can call on the command line to build an image. A container image is a stack consisting of multiple layers. Each instruction creates a layer.

When using a browser to access a containerized application built from a Nginx image, you will see the default Nginx welcome page. In this section, you will build a new image based on the Nginx image to change the welcome message to Hello, SWR!

Log in to the container engine as the root user.
Run the following commands to create an empty file named Dockerfile:

mkdir mynginx

cd mynginx

touch Dockerfile
Edit the Dockerfile.

vim Dockerfile

Add the following instructions to the Dockerfile:
```
FROM nginx
RUN echo '<h1>Hello, SWR!</h1>' > /usr/share/nginx/html/index.html
```
In the preceding instructions:
- FROM: creates a layer from the base image. A valid Dockerfile must start with a FROM instruction. In this example, the Nginx image is used as the base image.
- RUN: executes a command to create a layer. One of its syntax forms is RUN <command>. In this example, the echo command is executed to display Hello, SWR!
Press Esc and enter :wq to save the settings and exit.
Run docker build [option] <context path> to build an image.

docker build -t nginx:v1 .
- -t nginx:v1: specifies the image name and tag.
- .: indicates the path where the Dockerfile is located. All contents in this path are packed and sent to the container engine to build an image.
Run the following command to check the created image. The command output shows that the Nginx image has been created with a tag of v1.

docker images

Creating an Image Package

This section describes how to compress a container image into a .tar or .tar.gz package.

Log in to the container engine as the root user.
Run the following command to check images:

docker images

Check the name and tag of the image to be compressed.
Run the following command to compress the image into a package:

docker save [OPTIONS] IMAGE [IMAGE...]

OPTIONS: You can set this to --output or -o, indicating that the image is exported to a file.

The file should be in either .tar or .tar.gz.

When using docker save to create an image package, use {image}:{tag} instead of image id. Otherwise, the package cannot be uploaded on the SWR page.

Example:
```
$ docker save nginx:latest > nginx.tar
$ ls -sh nginx.tar
108M nginx.tar

$ docker save php:5-apache > php.tar.gz
$ ls -sh php.tar.gz
372M php.tar.gz

$ docker save --output nginx.tar nginx
$ ls -sh nginx.tar
108M nginx.tar

$ docker save -o nginx-all.tar nginx # Packages all Nginx versions.
$ docker save -o nginx-latest.tar nginx:latest
```