Getting Started with Docker

Published Sep 19, 2017

This is the first post on DevOps tools that I will be talking about. I will be explaining how to use automation tools to deploy scaling, contain applications, build alternatives, and perform data analytics of logs and develop enterprise cost effective automations tools.

Let's begin with DOCKER.

If you are using centOS, follow the instructions below:

[root@tito ~]# cd /etc/yum.repos.d
[root@tito yum.repos.d]# vi docker.repo

Add the below inside the newly created docker.repo.

[dockerrepo]
name=Docker Repository
baseurl=https://yum.dockerproject.org/repo/main/centos/7/
enabled=1
gpgcheck=1
gpgkey=https://yum.dockerproject.org/gpg

Next, run an update.

[root@tito ~]# yum update

Once updated, proceed to installing the docker-engine.

[root@tito ~]# yum install -y docker-engine

Proceed with enabling systemctl, which will create a link to start up Docker, to start up Docker upon reboot.

[root@tbola451 yum.repos.d]# systemctl enable docker
Created symlink from /etc/systemd/system/multi-user.target.wants/docker.service to /usr/lib/systemd/system/docker.service

Now, let's proceed to running Docker as a daemon service.

[root@tito ~]# systemctl start docker

YAY, BINGO!!! Your Docker is running.

Verify by checking your Docker version.

[root@tbola451 ~]# docker --version
Docker version 17.05.0-ce, build 89658be

Your Docker is up and running. You can view your Docker images, which are empty for now because your Docker is newly installed.

Below is what mine looks like, I don't have any images yet

[root@tbola451 ~]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE

Hmmm, notice how I am using root user? That's not cool in terms of security. Therefore, I will back out/exit root and become a regular user (the user assigned for Docker).

[root@tbola451 ~]# exit 
logout
[user@tbola451 ~]$ docker images
Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.29/images/json: dial unix /var/run/docker.sock: connect: permission denied

Oops, now you can see that you can't connect to the Docker daemon when you tried to run the docker images command.

What you need to do is become the root user again.

Yeah, I know that I said to exit root before, but believe me, you really need to become root this time because we will be doing some file ownership modification. Sounds cool, right?

[user@tbola451 ~]$ su -
Password: 
[root@tbola451 ~]# cd /var/run/
[root@tbola451 run]# ls -la dock*
[root@tbola451 run]# ls -la dock*
-rw-r--r--. 1 root root     4 Aug 30 01:50 docker.pid
srw-rw----. 1 root docker  0 Aug 30 01:50 docker.sock

docker:
total 0
drwx------.  6 root root 120 Aug 30 01:50 .
drwxr-xr-x. 28 root root 900 Aug 30 01:50 ..
drwx------.  3 root root 100 Aug 30 01:50 libcontainerd
drw-------.  2 root root  60 Aug 30 01:50 libnetwork
drwx------.  2 root root  40 Aug 30 01:50 plugins
drwx------.  2 root root  40 Aug 30 01:50 swarm

We need to be able to connect to this sock file srw-rw----. 1 root docker 0 Aug 30 01:50 docker.sock. But, it seems like it's owned by the root and docker group, so only root can use/connect to it (root created it, so selfish of root).

Let's add a user to the Docker group, my username is user.

[root@tbola451 run]# cat /etc/group |grep docker
docker:x:988:
[root@tbola451 run]# usermod -a -G docker user
[root@tbola451 run]# cat /etc/group |grep docker
docker:x:988:user

Nice! It seems like we fixed that pretty nicely. Exit and log in as yourUser. Mine is user and confirm. Below is my output.

[user@tbola451 ~]$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
[user@tbola451 ~]$ 
[here]()

Skipped the above? Follow the below instructions for quick Docker installation.

[root@tbola451 ~]# cd /etc/yum.repos.d
[root@tbola451 yum.repos.d]# vi docker.repo
*****Add the below inside the newly created docker.repo****
[dockerrepo]
name=Docker Repository
baseurl=https://yum.dockerproject.org/repo/main/centos/7/
enabled=1
gpgcheck=1
gpgkey=https://yum.dockerproject.org/gpg
*********************************************
[root@tbola451 yum.repos.d]# yum update
[root@tbola451 yum.repos.d]#yum install -y docker-engine
[root@tbola451 yum.repos.d]# systemctl enable docker
[root@tbola451 yum.repos.d]# systemctl start docker
[root@tbola451 ~]# docker --version
[root@tbola451 ~]# docker images