RHEL7: How to get started with Docker.

Presentation of Docker

Docker is a platform for developers and sysadmins to develop, ship, and run applications.

Docker allows you to create lightweight, portable, self-sufficient containers from any application and lets you get your code tested and deployed into production as fast as possible.

Installation

To install Docker, type:

# yum install -y docker

Until recently, Red Hat advised to stop the firewalld service because there was some incompatibility with Docker. To disable the firewalld service, type:

# systemctl disable firewalld && systemctl stop firewalld

Note: According to this bug report, this shouldn’t be necessary any more.

To enable and start Docker, type:

# systemctl enable docker && systemctl start docker

To get the installed version of Docker, type:

# docker version
Client version: 1.2.0
Client API version: 1.14
Go version (client): go1.3.3
Git commit (client): 2a2f26c/1.2.0
OS/Arch (client): linux/amd64
Server version: 1.2.0
Server API version: 1.14
Go version (server): go1.3.3
Git commit (server): 2a2f26c/1.2.0

To get some additional information, type:

# docker info
Containers: 1
Images: 3
Storage Driver: devicemapper
Pool Name: docker-253:0-31125-pool
Pool Blocksize: 64 Kb
Data file: /var/lib/docker/devicemapper/devicemapper/data
Metadata file: /var/lib/docker/devicemapper/devicemapper/metadata
Data Space Used: 557.4 Mb
Data Space Total: 102400.0 Mb
Metadata Space Used: 0.9 Mb
Metadata Space Total: 2048.0 Mb
Execution Driver: native-0.2
Kernel Version: 3.10.0-123.9.3.el7.x86_64
Operating System: CentOS Linux 7 (Core)

Docker Image Download

If you’ve got 1GB of free disk space on the / partition, to install a CentOS 7 distribution, type:

# docker pull centos:centos7
Pulling repository centos
ae0c2d0bdc10: Download complete
511136ea3c5a: Download complete
5b12ef8fd570: Download complete

Note: If you specify centos instead of centos:centos7, you will get centos5, centos6, centos7 and latest (equals to centos7) images. Be prepared to allow 2GB of free disk space.

To display the list of locally available images, type:

# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
centos              centos7             ae0c2d0bdc10        2 weeks ago         224 MB

Note: To remove this image, type # docker rmi ae0c2d0bdc10 or # docker rmi centos:centos7.

To test your new image, type:

# docker run centos:centos7 /bin/ping google.com -c 2
PING google.com (173.194.40.136) 56(84) bytes of data.
64 bytes from par10s10-in-f8.1e100.net (173.194.40.136): icmp_seq=1 ttl=54 time=12.5 ms
64 bytes from par10s10-in-f8.1e100.net (173.194.40.136): icmp_seq=2 ttl=54 time=12.6 ms

Container Creation

We are going to create a container (here called python_web) running a web server in Python on the 8000 port (/bin/python -m SimpleHTTPServer 8000).

This example is taken from a Red Hat article about Docker.

# mkdir -p /var/www/html
# echo "Server up and running" > /var/www/html/test.txt
# restorecon -R /var/www
# docker run -d -p 8000:8000 --name="python_web" -v /usr/sbin:/usr/sbin -v /usr/bin:/usr/bin \
-v /usr/lib64:/usr/lib64 -w /var/www/html -v /var/www/html:/var/www/html centos:centos7 \
/bin/python -m SimpleHTTPServer 8000
# netstat -tupln | grep 8000
tcp6       0      0 :::8000                 :::*            LISTEN      27739/docker
# curl localhost:8000/test.txt
Server up and running

Sources: Docker web site and Red Hat’s article about Docker.

Additional Resources

You can also:

• watch this Red Hat video giving a Docker overview (5min/2014),
• read this Red Hat article by Jeremy Eder about a Comprehensive Overview of Storage Scalability in Docker,
• read this nice presentation from Red Hat Etsuji Nakai about Linux Container Technology inside Docker with RHEL 7 (2015),
• read this Red Hat article about Docker Formatted Container Images on Red Hat Systems,
• read this presentation by Docker Jerome Petazzoni about Docker Storage Drivers,
• watch this presentation by Red Hat Chris Negus about Linux Containers Overview (20min/2015).,
• read this Red Hat article about the History of Containers,
• read this short tutorial if you want to start a docker container at boot time as a linux service,
• read this Tecmint tutorial about Installing Docker and Learning Basic Container Manipulations,
• read this article about why you shouldn’t use devmapper with Docker or this one about Running Docker on Loopback in Production,
• read this good tutorial about Docker for beginners,
• read this DigitalOcean tutorial about Installing and Using Docker,
• read this page about Some tools for working with Docker images,
• read this article by Dan Walsh about the way the Atomic Project deals with Docker patches,
• read this other article by Dan Walsh about Running systemd in a non-privileged container,
• read this article by Jeremy Eder about Getting overlay2 speed and density with devicemapper in Docker,
• read this Red Hat article about the different kinds of available Docker packages,
• read this complete presentation about What is Docker and How to install it,
• read this DigitalOcean tutorial about Configuring the Linux Firewall for Docker Swarm on CentOS 7,
• watch this Docker workshop (88min/2016) (details here),
• watch this Red Hat video presenting a Docker Overview (6min/2017),
• have a look at the Docker company website and play with containers,
• read these Red Hat articles about container capabilities:
  • Find what capabilities an application requires to successful run in a container,
  • What capabilities do I really need in my container?
• have a look at buildah, the new Red Hat tool, to build (OCI) compliant images and containers,
• read these articles by Dan Walsh about Linux containers evolution and what tools RedHat puts in place in the Docker ecosystem,
• have a look at this series by Matt Micene about Containing System Services in RHEL: part1, part2,
• have a look at this RHEL push plugin that blocks any RHEL based image to be pushed to the default docker.io registry preventing users to violate the RH subscription agreement,
• watch this Brendan Gregg‘s video about Container Performance Analysis (42min/2017),
• have a look at this Red Hat article on How is the docker container runtime supported in RHEL 7?