Overview of Docker and containers

Regarding this article

Created for in-house young study sessions It explains as easily as possible, understanding the outline, building the environment, and actually operating it.

environment

Windows 10
Docker for Windows 2.3.0.4 stable edition
Authentication proxy exists (items are separated, so if you do not have a proxy, you can skip it)

Overview of Docker and containers

What is a container?

One of the virtualization technologies

What is Docker

One of the container engines shown below

Difference between conventional virtualization (hypervisor type) and container

Since the container shares the kernel of the host OS, resource usage is low and startup is quick.
Dependencies can be packaged inside a container
→ Containerized applications can be executed in different environments (portability)
With the conventional hypervisor type, when operating in another environment, it was necessary to obtain materials and manually build the environment.

The story of the OS and the OS kernel

OS kernel
The one that plays the main role in the OS that mediates between software and hardware.
Well-known kernels include Linux and Windows kernels (?)
OS
Software (UI, drivers, developer tools, etc.) on top of the kernel
The Linux kernel is also divided into OSs such as Ubuntu, CentOS, and RHEL depending on the software.

Docker for Windows environment construction

Enable Hyper-V

Since it is necessary to enable Hyper-V to run Docker on Windows, Execute the following command with powershell opened with administrator privileges, Enable Hyper-V (PC restart required)

>Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V -All

After restarting, check if Hyper-V is enabled in BCDEdit * Execute the following command with powershell, If it is output by hypervisorlaunchtype Auto, it has been successfully enabled.

Command line tool for managing boot configuration data (BCD)

bcdedit /enum | find '"hypervisorlaunchtype"'

If it is off, execute the following command and restart again.

bcdedit /set hypervisorlaunchtype auto

Installation & setup of docker for windows

Get Docker for Windows (2.3.0.4 stable edition) from the link below https://docs.docker.com/get-docker/

Reboot after installation After restarting, start Docker and the Docker startup procedure will be displayed After the installation is complete, docker for windows will be added to the indicator at the bottom right of the screen

Because it requires a lot of memory to start an image or container Change the memory allocation from 2GB to 4GB from [Setting] → [Resources]

The following is only for those who need proxy authentication

Enter the following settings in [Setting] → [Resources] → [PROXIES]. -Http: // : @ proxy host name: proxy port number/set

Why you need Hyper-V (hypervisor) even though it is a container

Hyper-V is a hypervisor, isn't it necessary for containers? You might think This is because the Docker container is based on Linux and requires a Linux kernel. Docker for Windows builds a Linux OS with Hyper-V on Windows OS, The Linux kernel on that Hyper-V is shared by the container

Once you have prepared the operating environment for Docker, you can run your favorite container. Containers can be obtained from a management location on the Internet called Docker Hub (* described later) At this time, the container is distributed in a snapshot-like format called a container image. After acquiring the image, it can be operated as a container by executing it.

Docker operation

DockerHub Container images can be obtained mainly from a management location on the net called Docker Hub Only image search is possible without user registration Here you can check the image name, provider, latest version, etc. https://hub.docker.com/

Get Docker image-Run container

Once you get docker for Windows, you can run docker commands from the command prompt Actually get a lightweight linux image called alpine from docker hub and run it


>docker pull alpine:latest
latest: Pulling from library/alpine
801bfaa63ef2: Pull complete                                                                                                                                                                                                                  Digest: sha256:3c7497bf0c7af93428242d6176e8f7905f2201d8fc5861f45be7a346b5f23436
Status: Downloaded newer image for alpine:latest
docker.io/library/alpine:latest
 
>docker images
REPOSITORY                           TAG                    IMAGE ID            CREATED             SIZE
alpine                               latest                 389fef711851        2 weeks ago         5.58MB
 
>docker run -it  -d  alpine:latest  /bin/sh
 
>docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES
c3a9d3cc09f4        alpine:latest       "/bin/sh"                6 seconds ago       Up 3 seconds                                 loving_mendeleev
 
docker exec -it c3a9d3cc09f4 /bin/sh
/ # ls
bin    dev    etc    home   lib    media  mnt    opt    proc   root   run    sbin   srv    sys    tmp    usr    var
/ # exit

The explanation of each command is as follows

docker pull
Getting the image from docker hub
Specify the image version with a tag, otherwise it will automatically become the latest version
docker images
You can check the list of images saved locally
docker run [optional] command
Starting the docker image as a container
By adding the -it option, standard input / output can be performed in the container.
You can also specify the command to move at login with the command.
In/bin/sh, you can start a shell, access docker, and then enter commands.
-d specifies to start in the background
docker ps
Get a list of running containers
docker exec [optional] command
Go inside the running container
You can exit the container with exit

Dockerfile

When actually creating a container, in addition to the base image Often create a container with the necessary middleware and apps It is possible to operate inside the started container, When you create a configuration as a Dockerfile, You will be able to set up and copy resources automatically

Launching a web server container using Dockerfile

Here is an example of creating a simple web server container

`Dockerfile`


#Use image of web server nginx
#Pull the image specified here from docker hub
FROM nginx:alpine
#You can copy materials from a local terminal to a container environment with ADD
#/usr/share/nginx/html is the place to store html to be displayed by nginx
ADD ./index.html /usr/share/nginx/html
#Free up 80 ports in the container
EXPOSE 80
#Set the entry point for the container
ENTRYPOINT /usr/sbin/nginx -g "daemon off;" -c /etc/nginx/nginx.conf

`index.html`


hello world,Docker

After creating the above file, execute the following command in the saved directory

Working folder/◀ Start command prompt here ├ Dockerfile └index.html

>docker build -t myimage .
Sending build context to Docker daemon  4.096kB
Step 1/5 : FROM nginx:alpine
 ---> 629df02b47c8
Step 2/5 : CMD echo "now running..."
 ---> Using cache
 ---> 2b4f225ff66e
Step 3/5 : ADD ./index.html /usr/share/nginx/html
 ---> Using cache
 ---> 8de80809c52c
Step 4/5 : EXPOSE 80
 ---> Using cache
 ---> 90168e587d3b
Step 5/5 : ENTRYPOINT /usr/sbin/nginx -g "daemon off;" -c /etc/nginx/nginx.conf
 ---> Running in eb60ad7be198
Removing intermediate container eb60ad7be198
 ---> d4d131ab1d24
Successfully built d4d131ab1d24
Successfully tagged myimage:latest
 
>docker run --name mycontainer -d -p 30080:80 myimage

docker build -t path
Generate an image based on the contents of Dockerfile
-t is an option to name the image you create
Image name can be set freely
In the path, specify the path of the Dockerfile used for build
Since it is saved in the current this time, specify [.]
docker run --name -d -p 30080: 80
Create a container based on the image name
--name is an option to name the container
-p is a setting that exposes the container port to the host
Release 80 ports of the container with Dockerfile,
Connecting to port 30080 on the host will connect to port 80 on the container After starting the container, when I tried to access it, the web server was started and the html created earlier was displayed.

Impressions of actually using the container

Because the project I currently belong to uses various technologies It was difficult to build the environment one by one, but when using Docker, If you generate a Dockerfile and put it in the source repository I find it very useful because each member can create a container environment and move their hands. Actually, I use a technology called docker-compose that can set up multiple containers. I'm exhausted so please refer to another article Also, when it comes to actual operation, it is essential to use orchestration tools such as k8s. I thought that this level of knowledge was sufficient for light movements such as feasibility studies.