What is Podman?

Docker bases all its operation on a process (daemon) that manages the containers. This process is getting bigger and bigger over time and this can be a problem. So Podman uses the fork/exec model that allows it to run using a smaller amount of resources.

The main driver of the project is Red Hat that has seen how in this distribution and the derivatives like CentOS have been replaced Docker with Podman. However, the images and many commands are compatible which reduces the learning curve.

One of the main differences is the path where Podman saves the images.

So in short, Podman is a container integration engine. It allows you to manage them in much the same way as Docker. So it’s a simple transition.

Installing Podman on OpenSUSE 15.1

Podman has strong documentation where they explain, among other things, how to install it from the source code. However, let’s do a search within the official OpenSUSE repositories to see.

So, open a terminal session or connect to your server using SSH.

:~$ sudo zypper search podman
Loading repository data…
 Reading installed packages…
 S | Name              | Summary                                                               | Type   
 --+-------------------+-----------------------------------------------------------------------+--------
   | podman            | Daemon-less container engine for managing containers, pods and images | package
   | podman-cni-config | Basic CNI configuration for podman                                    | packageLoading repository data…
 Reading installed packages…
 S | Name              | Summary                                                               | Type   
 --+-------------------+-----------------------------------------------------------------------+--------
   | podman            | Daemon-less container engine for managing containers, pods and images | package
   | podman-cni-config | Basic CNI configuration for podman                                    | package

As we can see in the image and in the standard output, Podman is in the official OpenSUSE 15.1 repositories, so it is best to install it from there as there are no external pre-compiled binaries.

To do this, just use the following command:

:~$ sudo zypper in podman
Loading repository data…
 Reading installed packages…
 Resolving package dependencies…
 The following 16 NEW packages are going to be installed:
   catatonit cni cni-plugins criu libcontainers-common libnet9 libostree-1-1 libprotobuf-c1 libpython2_7-1_0 podman podman-cni-config python2-ipaddr python2-protobuf
   python-base runc slirp4netns
 The following 3 recommended packages were automatically selected:
   cni-plugins criu podman-cni-config
 16 new packages to install.
 Overall download size: 36,1 MiB. Already cached: 0 B. After the operation, additional 138,7 MiB will be used.
 Continue? y/n/v/…? shows all options:

At the end of the installation, Podman will be ready for work.

Testing Podman on OpenSUSE 15.1

The installation has been completed but we are going to test the operation.

To do so, I will download the image of Alpine. It is light and simple and will help us to test the operation of Podman.

:~$ sudo podman pull alpine
Trying to pull docker.io/alpine:latest…Getting image source signatures
 Copying blob c9b1b535fdd9: 2.67 MiB / 2.67 MiB [============================] 8s
 Copying config e7d92cdc71fe: 1.48 KiB / 1.48 KiB [==========================] 0s
 Writing manifest to image destination
 Storing signatures
 e7d92cdc71feacf90708cb59182d0df1b911f8ae022d29e8e95d75ca6a99776a

To check all the images that are downloaded to the system, execute the following command:

:~$ sudo podman images 
REPOSITORY                 TAG      IMAGE ID       CREATED       SIZE
 docker.io/library/alpine   latest   e7d92cdc71fe   5 weeks ago   5.86 MB

And finally, run Alpine’s image. Once inside the image, run a command to prove we’re at Alpine:

:~$ sudo podman run -it --rm docker.io/library/alpine /bin/sh
/ # cat /etc/os-release 
NAME="Alpine Linux"
ID=alpine
VERSION_ID=3.11.3
PRETTY_NAME="Alpine Linux v3.11"
HOME_URL="https://alpinelinux.org/"
BUG_REPORT_URL="https://bugs.alpinelinux.org/"
/ #

So, Podman is ready for the job.

Conclusion

Podman emerges as an alternative to Docker. As I always say, the competition only benefits the user and if Podman improves on the already excellent one made by Docker then it is welcome. So we’ll keep track of the project and now you know how to install it in OpenSUSE 15.1

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In short, Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications. The most important factor that sets Kubernetes apart from other cloud computing solutions is that it was built to work with Docker. That’s why it’s the most used tool to deploy Dockers applications.

Now, I will show you how to install it on CentOS 7.

0. Prerequisites

The installation is not as complicated as it seems, however, you should have a little knowledge about Terminal and commands. Also required is a computer that will serve as a server and another that will serve as a node. The central idea is to add them in a cluster.

Both computers run CentOS 7 and it’s on a local network. Let’s start.

1. Install Kubernetes on the server

As I said before the idea is to make a cluster, for it, first we must configure the server where you will run Kubernetes. First, you have to disable SELinux and apply various rules in the Firewall for everything to work well. Note: all commands must be run as root user.

:~# hostnamectl set-hostname osradar
:~# exec bash
:~# setenforce 0
:~# sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux

Next, set the firewall rules:

:~# firewall-cmd --permanent --add-port=6443/tcp
:~# firewall-cmd --permanent --add-port=2379-2380/tcp
:~# firewall-cmd --permanent --add-port=10250/tcp
:~# firewall-cmd --permanent --add-port=10251/tcp
:~# firewall-cmd --permanent --add-port=10252/tcp
:~# firewall-cmd --permanent --add-port=10255/tcp
:~# firewall-cmd --reload
:~# modprobe br_netfilter
:~# echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables

In case you don’t have a DNS server configured. Edit the file /etc/hosts and add the information of your node and server.

:~# nano /etc/hosts

And add the following:

192.168.1.8 osradar
192.168.1.9 node1

Of course, replace the configuration with yours depending on the IP addresses and hostname chosen.

2. Install Kubernetes

In order to install Kubernetes on CentOS 7, you must add its repository. With this, the installation will be quick and easy. Run

:~# nano /etc/yum.repos.d/kubernetes.repo

And put the following:

[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
enabled=1
gpgcheck=1
repo_gpgcheck=1
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg
https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg

Then, you can install it. Also, you have to install docker:

:~# yum install kubeadm docker

Then, start and enable both docker and kubectl services:

:~# systemctl enable docker
:~# systemctl start docker
:~# systemctl enable kubelet
:~# systemctl start kubelet

3. Initialize Kubernetes in CentOS 7

Now you can start Kubernetes with the next command:

.~# kubeadm init

If you see something like this, everything is OK.

As you can see from the image, you must now execute these commands:

:~# mkdir -p $HOME/.kube
:~# cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
:~# chown $(id -u):$(id -g) $HOME/.kube/config

The next step is to check the status of the clusters and pods

:~# kubectl get nodes
:~# kubectl get pods --all-namespaces

To ensure that there is communication between the nodes of the cluster, you have to run the following:

:~# export kubever=$(kubectl version | base64 | tr -d '\n')
:~# kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$kubever"

Now, re-run the command to show all the pods.

:~# kubectl get pods --all-namespaces

Everything is going OK.

4.- Working on the node or nodes

In this step, you must work on the number of nodes you want to configure. In this case, it will be only one, but remember that they can be more.

At each node, run the following. First, change the hostname and set the firewall rules:

:~# setenforce 0
:~# sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux
:~# firewall-cmd --permanent --add-port=10250/tcp
:~# firewall-cmd --permanent --add-port=10255/tcp
:~# firewall-cmd --permanent --add-port=30000-32767/tcp
:~# firewall-cmd --permanent --add-port=6783/tcp
:~# firewall-cmd  --reload

Next, install Kubernetes.

:~# cat <<EOF > /etc/yum.repos.d/kubernetes.repo

And add the following:

> [kubernetes]
> name=Kubernetes
> baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
> enabled=1
> gpgcheck=1
> repo_gpgcheck=1
> gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg
>         https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
> EOF

Next, install it:

:~# yum install kubeadm docker

Then, enable and start the services:

:~# systemctl enable docker
:~# systemctl start docker
:~# systemctl enable kubelet
:~# systemctl start kubelet

Finally, join to the master node.

:~# kubeadm join --token xnxlx4.k6qupcvb9g7tq2ti 192.168.1.8

Conclusion

As you can see, the process of installing Kubernetes on CentOS 7 is simple and we are talking about a very powerful tool in the Linux world.

We want to know about you, have you used Kubernetes? do you use Docker?

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Docker is an open source project that automates the deployment of applications within software containers, providing an additional layer of Virtualization abstraction and automation at the operating system level in Linux. The work of system administrators is made easier because the software is implemented in the same way it was tested.

Containers vs. Virtual Machines

When we read the concept of containers, it is highly probable that we relate it to that of virtual machines, however, they are different things.

Docker containers share resources with the operating system on which they run. While virtual machines isolate themselves from the host system and communicate with Hypervisor.

But the most relevant difference between these two concepts is that virtual machines focus on the virtualization of the operating system and the containers in the Application and their portability.

These containers have some main characteristics:

• The container can be extended on any system that supports the technology
• It’s light. It takes up far less space than any other virtualization system
• Containers running on the same machine share the same Operating System

Installing Docker CE on CentOS 7

Adding the official Docker repository

There are several versions of docker, such as the enterprise version aimed specifically at companies. And another version that is communal focused to the tests and to enthusiasts who want to know the technology

Docker’s official documentation indicates that there are 3 ways to install it on our Server with CentOS 7. The first one is downloading the packages and then installing them manually; the second one is through automated scripts that download and install Docker automatically; the third one is adding the stable repository and installing it with Yum from the terminal, this is the way it will be installed.

First we must update the system to get the latest version of the necessary packages. With root user privileges, we proceed to execute:

            yum update

Once the system is updated, we proceed to install some packages necessary to have a smooth installation.

              yum install yum-utils device-mapper-persistent-data lvm2

And now we can add the desired repository:

             yum-config-manager –add-repo https://download.docker.com/linux/centos/docker-ce.repo

We check that the repository has been added with:

             yum repolist

The repository was correctly added as we can see in the previous image. We can continue with the installation.

Docker installation

To install Docker, we proceed to execute the following command:

                  yum install docker-ce

Now, we must start your service with the command:

             systemctl start docker

The repository was correctly added as we can see in the previous image

Now we can test the installation. Run the command:

              docker run hello-world

We can say then, that Docker has been installed correctly.

Getting started

One of the first things we can do is to search for a container related to a distribution or an application, we can do it with the following command:

             docker search ubuntu

Where ubuntu is the search criteria and will show you all the ubuntu related containers that are available

And for example, to load the debian container, we run:

            docker pull i383/debian

Now, we checked the images we have in the system:

            docker images

Next we must enter the container or image and we can do it in two ways: through the formula repository+tag; or with the image id.

In this case it could be:

              docker run -i -t 6ed200f7bf1c /bin/bash

or:

               docker run -i -t i386/debian:lastest

And to exit we have two options: the first is to press CTRL+D but this stops the execution of the container and in many cases it is not convenient to do this; the other option is to press CTRL and without releasing press P and then Q successively.

Obviously with this we have not become a Docker expert but at least it gives us an idea of what the technology is like.

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