It occurred to me that if you want to start using Docker there are plenty examples that use Ubuntu as a base platform. I read a book called
Learning Docker that assumes Ubuntu for the examples, for instance. I know I am quite stubborn, a "know-it-better" person, but I want to be able to do the same on Oracle Linux.
Docker on Oracle Linux turns out not too complicated. But I ran in to a caveat that I solved and want to share.
I use Vagrant to bring up an Oracle Linux Box, based on a Vagrantfile that
prepares the box.With that as a starting point, I created a script that does the complete docker installation. In the following I'll build it up for you, step by step. I'll add my project to GitHub, and provide a link to the complete script in the end.
Init
First some initialization and a function to read the property file:
#!/bin/bash
SCRIPTPATH=$(dirname $0)
#
# Install docker on Oracle Linux.
# @author: Martien van den Akker, Darwin-IT Professionals.
#
function prop {
grep "${1}" $SCRIPTPATH/makeDockerUser.properties|cut -d'=' -f2
}
#
DOCKER_USER=$(prop 'docker.user')
DOCKER_GROUP=docker
This sets the
$SCRIPTPATH property as the folder where the script resides, so I can refer to other files relative to that one.
The function prop alows me to get a property from a property file. A smart function that I got from a colleague (thanks Rob). Based on this property file called makeDockerUser.properties:
docker.user=oracle
docker.password=welcome1
I set the
DOCKER_USER and
DOCKER_GROUP properties.
The
DOCKER_GROUP property is hardcoded however, but that is the standard group that is created at installation of Docker to allow other users to use Docker.
Install Docker Engine
The first actual step is to install the docker engine. Now you can go for the community edition and I've seen that there are examples that pulls the docker-ce (docker Community Engine) for you. However, one of the reasons I am stubborn to stick with Oracle Linux (as you know a RedHat derivate) is that Oracle Linux is the flavor that is used with most of my customers. And if not, it is RedHat. And then I just want to rely on the standard repositories.
To install the docker engine, I have to add the
ol7_addons and the
ol7_optional_latest repositories. During my OL prepare script, I already added the
ol7_developer_EPEL repository. Then the
docker-engine package can simply be installed by yum:
#
echo 1. Install Docker Engine
echo . add ol7_addons and ol7_optional_latest repos.
sudo yum-config-manager --enable ol7_addons
sudo yum-config-manager --enable ol7_optional_latest
#
echo . install docker-engine
sudo yum install -q -y docker-engine
Install Curl
For most docker related actions, it is convenient to have curl installed as well:
#
echo 2. Install curl
sudo yum install -q -y curl
Add docker group to docker user
After the docker installation, we need to add the docker group to the docker user (in my case the sort-of default oracle user):
#
echo 3. Add ${DOCKER_GROUP} group to ${DOCKER_USER}
sudo usermod -aG ${DOCKER_GROUP} ${DOCKER_USER}
This allows the ${DOCKER_USER} (set in the initialization phase) to use the docker command.
Check the docker install
Now let's add a check if docker works:
#
echo 4. Check Docker install
docker --version
sudo systemctl start docker
sudo systemctl status docker
This lists the version of the installed docker, then starts the docker service and lists the status of the docker.
Change the location of the docker containers
When creating a docker container/image (I leave the difference for now), these are saved by default in the location
/var/lib/docker. The thing is that this is on the root disk of your installation. And it can grow quite big. For installations of oracle software for instance, I create an extra disk that I mount on
/app. It would be better to have a
/data mount point as well, but for now I stick with the
/app data. So, I want to have docker place my images on the secondary disk. One solution used by Tim Hall, see
here, is to create a second disk, format it with
BTRFS, and mount it simply to
/var/lib/docker.
I rather reconfigure docker to use another disk. This is taken from
this article.
To implement this, we first need to know which
storage driver Docker uses. We get this from the command
docker info, as follows:
echo 5. Change docker default folder
# According to oracle-base you should create a filesystem, preferably using BTRFS, for the container-home. https://oracle-base.com/articles/linux/docker-install-docker-on-oracle-linux-ol7.
# But let's stick with ext4.
## Adapted from https://sanenthusiast.com/change-default-image-container-location-docker/
echo 5.1. Find Storage Driver
GREP_STRG_DRVR=$(sudo docker info |grep "Storage Driver")
DOCKER_STORAGE_DRVR=${GREP_STRG_DRVR#*": "}
echo "Storage Driver: ${DOCKER_STORAGE_DRVR}"
This mentions me the
overlay2 driver.
Then we need to stop docker:
echo 5.2. Stop docker
sudo systemctl stop docker
And then create the folder where we want to store the images:
echo 5.3. Add reference to data folders for storage.
DOCKER_DATA_HOME=/app/docker/data
echo mkdir -p ${DOCKER_DATA_HOME}
sudo mkdir ${DOCKER_DATA_HOME}
Now I found a bit of a problem with my solution here. When I reconfigure docker to use my custom folder, it turns out that on my system the filesystem is not writable from the docker image. If you want to install software in your image, it of course wants to write the files. And this is prevented. After quite some searching, I came on
this question on stackoverflow. It turns out that
selinux enforces a policy that prevents writing of docker to a custom device. This can be simply circumvented by disabling the enforcing:
#
##https://stackoverflow.com/questions/30091681/why-does-docker-prompt-permission-denied-when-backing-up-the-data-volume
echo disable selinux enforcing
sudo setenforce 0
This disables, as said, the enforcing of selinux. I would say this should be a bit more nuanced. But I don't have that at hand. This however, solved my problem.
Now all is left to configure docker to use the custom folder. Docker is started using a script. In Oracle Linux this is quite conveniently setup. In the folder
/etc/sysconfig you find a few config scripts, amongst others a script called:
docker-storage. This is a proper to add options. When you set the
DOCKER_STORAGE_OPTIONS variable, it is added to the command line. So we simply need to add the line:
DOCKER_STORAGE_OPTIONS = --graph="/app/docker/data" --storage-driver=overlay2
, to the file
/etc/sysconfig/docker-storage. This can be done with the following snippet:
#
DOCKER_STORAGE_CFG=/etc/sysconfig/docker-storage
sudo sh -c "echo 'DOCKER_STORAGE_OPTIONS = --graph=\"${DOCKER_DATA_HOME}\" --storage-driver=${DOCKER_STORAGE_DRVR}' >> ${DOCKER_STORAGE_CFG}"
And then finish up with starting docker service again:
#
echo 5.4 Reload deamon
sudo systemctl daemon-reload
echo 5.5 Start docker again
sudo systemctl start docker
Conclusion
Last week I was at the #PaaSSummerCamp in Lisbon. I did some labs with my docker installation, that resulted in the
permission problem. As mentioned I resolved that and I could run the labs succesfully with docker containers from Oracle. So, I concluded that this script should suffice. You can download the complete script at my
GitHub vagrant repo.
