Let's create a Docker container that can connect to CentOS 8 with the minimum configuration by SSH

(2020/09/25) The troubleshooting part has been separated into the following articles. Cannot connect to VM with SSH connectable Docker container

Overview

I've been a little interested in Docker lately, but I haven't had a chance to come into contact with Docker at work so far, so I decided to study for myself. Google teachers and ancestors will introduce a lot of articles to build around CentOS 7, but since CentOS 8 has been released for a while (quite?), It's a new one, so it's a trial and error process. Let's play a little with the knowledge. [^ 1] This time, the goal is to create a container that can be connected by SSH, and to enable SSH access from the host to the container.

[^ 1]: CentOS 8 seems to come with a Docker-compatible system called Podman as standard equipment, so you may not need to use Docker.

environment

--Windows10 Home (1909) (host)

• VirtualBox 6.1.4 --CentOS 8.1.1911 (guest)
• Docker 19.03.8
• Docker Compose 1.25.4

procedure

VM boot

It may be easy to install by default, but for the time being, I decided to try how far it can be built with Minimal (minimum configuration). CentOS 8 uses a full-size image, and during installation there will be a place to select the configuration, so select the minimum configuration there. The construction procedure in VirtualBox is omitted. I referred to the following articles.

Reference: Build CentOS8 in Virtualbox environment Reference: CentOS8 at first glance

SSH connection related settings

After installing the OS, bring it from TeraTerm on the host side to a place where SSH connection is possible.

First, set up port forwarding on the VirtualBox side. It would be nice if SSH access was possible, but with the image below, I would like to be able to access the guest VM by specifying port 2222 and the container by specifying port 22222 when connecting.

Host --- Guest --- Container 2222 ----- 22 22222 --- 2222 --- 22

Therefore, in VirtualBox, set the association between 2222 and 22 and 22222 and 2222. The association between guest VM No. 2222 and container No. 22 will be performed later in the Docker-related settings.

Move to the settings on the guest VM side. First, set the firewall to allow SSH connections.

# firewall-cmd --add-service=ssh --permanent
# firewall-cmd --reload

Enable network interface.

# nmcli connection up enp0s3
# nmcli connection modify enp0s3 connection.autoconnect yes
# nmcli connection show enp0s3

Disable SELinux and restart.

# vi /etc/selinux/config
SELINUX=disabled
# reboot

Now you can SSH from the host side TeraTerm to the guest VM. When connecting, specify the IP address for the host name (192.168.11.4 in our environment), and specify the port as set for port forwarding in Virtual Box (2222 this time).

Introducing Docker

~~ This time, I will try it on the assumption that it will be built in an offline environment. ~~ </ font> I was thinking of building it in an offline environment until the middle of the process, but I ended up working in an online environment because external communication was absolutely necessary when starting the Docker container in the latter stage. Therefore, please forgive me though I am taking unnecessary steps for offline to the middle. (Maybe all the steps are rewritten online)

$ tar zxvf docker-19.03.8.tgz
-bash: tar:Command not found

$ sudo yum install tar
$ tar zxvf docker-19.03.8.tgz

$ sudo mv docker-compose-Linux-x86_64 /usr/local/bin/docker-compose
$ sudo chmod +x /usr/local/bin/docker-compose
$ sudo ln -s /usr/local/bin/docker-compose /usr/bin/docker-compose

$ sudo usermod -aG docker $USER

FROM alpine

#Introduced ssh and others
RUN set -x && apk update && apk upgrade \
  && apk add --no-cache openssh openrc \
  && apk add --no-cache bash \
  && apk add --update busybox-suid
RUN rc-update add sshd && rc-status
RUN mkdir -p /run/openrc/ && touch /run/openrc/softlevel

#sshd settings
RUN sed -i 's/^AllowTcpForwarding no/AllowTcpForwarding yes/g' /etc/ssh/sshd_config
RUN sed -i 's/^#PermitRootLogin prohibit-password/PermitRootLogin yes/g' /etc/ssh/sshd_config

#Created by general user
RUN adduser -D test

#Password setting
RUN echo 'root:root' | chpasswd
RUN echo "test:test" | chpasswd

#Hide banner when logging in
RUN echo "" > /etc/motd

#Start sshd and leave it as it is
CMD /etc/init.d/sshd start && tail -f /dev/null

version: '3.8'

services:
  test:
    build: .
    container_name: test
    hostname: test
    ports:
      - "2222:22" #Setting to associate guest VM with container port
    tty: true

[centos@dockertest ~]$ docker-compose build
[centos@dockertest ~]$ docker-compose up -d

test:~$