What is docker
Docker is a container-management system that helps us easily manage Linux Containers (LXC) in an easier and universal fashion. Docker is supported on many Linux platforms, such as RHEL, Ubuntu, Fedora, CentOS, Debian, Arch Linux, and so on. It is also supported on many cloud platforms, such as Amazon EC2, Rackspace Cloud, and Google Compute Engine.
Docker Editions
Docker is available in 2 editions namely:
1. Community Edition (CE): do-it-yourself, community supported version of Docker that’s available for free of cost.
2. Enterprise Edition (EE) : Officially supported and paid version from Docker.
Docker Terminologies
1. Docker Images : It is a collection of files like libraries, binaries, and other dependencies just needed to run the application. These files in the Docker image are read-only and hence the content of the image cannot be altered.
2. Docker Containers : The docker images are read-only and stateless. The docker containers on the other hand are spun-off from docker image and adds a read-write layer on top of it.
3. Docker Registry : Docker images can be stored in order to be publicly or privately in a Docker registry. Docker Registry could be hosted by a third party as a public or private registry, like Docker Hub.
Pre-requisites
Before installing docker engine, lets verify if you have all the pre-requisites met.
1. Docker is only supported on 64-bit architecture. So make sure you do not have a 32-bit system at hand. To check the architecture use the below command.
# uname -i x86_64
2. Docker is supported on kernel version 3.8 or later. To check the kernel version, run the following command:
# uname -r 3.10.0-693.5.2.el7.x86_64
3. The kernel should have a storage backend such as DeviceMapper. To verify use either of the below commands.
# rpm -qa | grep mapper device-mapper-1.02.140-8.el7.x86_64 device-mapper-libs-1.02.140-8.el7.x86_64
or
# grep device-mapper /proc/devices 253 device-mapper
Install the required packages
1. As specified in the pre-requisite section above, we need to have a storage backend such as DeviceMapper. device-mapper-persistent-data and lvm2 packages are required by the devicemapper storage driver.
# yum install -y device-mapper-persistent-data lvm2
2. Also install the yum-config-manager utility provided by yum-utils package in order to setup the docker repository in the next section.
# yum install -y yum-utils
Setup the repository
Use the command below to setup the repository for docker.
# yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
Installing docker
Finally coming to the last step of actaully installing the Community Edition of docker.
# yum install docker-ce
Installing Docker using an automated script
There also an automated way of installing docker, which installs the pre-requisite packages as well as the docker engine for you. The script is universal and works for all the linux distributions available. To install docker using the automated script use either of the below commands:
$ sudo curl -sSL https://get.docker.io/ | sh
or
sudo wget -qO- https://get.docker.io/ | sh
Start/Stop Docker service
You will have to start the docker service after you have finished installing docker engine.
# systemctl start docker
To enable the service start at boot time:
# systemctl enable docker
To stop the docker service, use the command below.
# systemctl stop docker
Verify installation
You can verify the docker installation by viewing the version of the docker engine installed by using either of the below commands.
# docker info Containers: 0 Running: 0 Paused: 0 Stopped: 0 Images: 0 Server Version: 17.10.0-ce ...
# docker --version Docker version 17.10.0-ce, build f4ffd25
Update docker
To update docker to the latest version, you can use the yum update command.
# yum -y update docker