Monitor Network Device Configurations with RANCID on CentOS 7. Next we will want to download ViewVC version is 1.1.23. ViewVC (formerly ViewCVS) is an open source tool for viewing the contents of CVS and SVN repositories using a web browser. It allows looking at specific revisions of files as well as side-by-side diffs of different revisions.
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Kubernetes is an open-source system used for automating the deployment, scaling, and management of containerized applications. Kubernetes is enterprise-ready and can be installed on various platforms. I've already touched on how to get Kubernetes up and running on Ubuntu Server (see 'How to quickly install Kubernetes on Ubuntu'). This time around, I'm going to walk you through the process of setting up a Kubernetes cluster on CentOS 7. This makes for an outstanding one-two punch for your containerized applications.
SEE: Quick glossary: Storage (Tech Pro Research)
What you'll need
I'll be demonstrating with three CentOS 7 servers (at the following IP addresses):
- kubemaster: 192.168.1.99
- kube2: 192.168.1.109
- kube3: 192.168.1.167
Make sure to change the IP addresses to fit your needs. You'll also need root access on all three servers. I do suggest first testing this on virtual machines, before attempting the installation on production servers.
With that said, let's install.
Pre-installation configuration
The first thing you want to do is configure your /etc/hosts file, so that each machine can ping one another via hostname. So on each machine, issue the su command (to change to the root user) and then edit the file with the command nano /etc/hosts. At the end of the file, append the following (again, adjusting the IP addresses to fit your needs):
Save and close that file.
Disable SELinux and swap
Now we need to disable both SELinux and swap. On all three machines, issue the following commands:
Next, disable swap (on all three machines) with the following command:
We must also ensure that swap isn't re-enabled during a reboot on each server. Open up the /etc/fstab and comment out the swap entry like this:
Enable br_netfilter
For our next trick, we'll be enabling the br_netfilter kernel module on all three servers. This is done with the following commands:
Install Docker-ce
It's time to install the necessary Docker tool. On all three machines, install the Docker-ce dependencies with the following command:
Next, add the Docker-ce repository with the command:
Install Docker-ce with the command:
Install Kubernetes
This is also done on all three servers. First we need to create a repository entry for yum. To do this, issue the command nano /etc/yum.repos.d/kubernetes.repo and then add the following contents:
Save and close that file. Install Kubernetes with the command:
Once the installation completes, reboot all three machines. As soon as each machine has rebooted, log back in and su to the root user.
Cgroup changes
Now we need to ensure that both Docker-ce and Kubernetes belong to the same control group (cgroup). By default, Docker should already belong to cgroupfs (you can check this with the command docker info | grep -i cgroup). To add Kubernetes to this, issue the command:
Restart the systemd daemon and the kubelet service with the commands:
Initialize the Kubernetes cluster
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We're now ready to initialize the Kubernetes cluster. This is done on kubemaster (and only on that machine). On kubemaster, issue the command (again, adjusting the IP addresses to fit your needs):
When this completes (it'll take anywhere from 30 seconds to 5 minutes), the output should include the joining command for your nodes (Figure A).
Figure A
Once that completes, head over to kube2 and issue the command (adjusting the IP address to fit your needs):
Where TOKEN and DISCOVERY_TOKEN are the tokens displayed after the initialization command completes.
Configuring Kubernetes
Before Kubernetes can be used, we must take care of a bit of configuration. Issue the following three commands (to create a new .kube configuration directory, copy the necessary configuration file, and give the file the proper ownership):
Deploy flannel network
Now we must deploy the flannel network to the cluster with the command:
Checking your nodes
Once the deploy command completes, you should be able to see both nodes on the master, by issuing the command kubectl get nodes (Figure B).
Figure B
All ready
Congratulations, you now have a Kubernetes cluster ready for pods. I'll be demonstrating how to deploy your first pod when next we visit the Kubernetes topic. Until then, happy clustering!
Also see
- How to deploy NGINX on a Kubernetes cluster (TechRepublic)
- 10 Kubernetes tips for getting the most out of the open source container system (TechRepublic)
- How to use Antsle to quickly deploy a virtual machine (TechRepublic)
- How to easily edit a network connection on a CentOS 7 minimal installation (TechRepublic)
- Red Hat introduces Kubernetes Operators software development toolkit (ZDNet)
The preferred way to install software on your CentOS system is to use the provided package management tools. CentOS uses the Red Hat Package Management (RPM) system and YUM as a front end to it. YUM is the preferred tool for installing software on your system. Online documentation for YUM is available here:
http://www.centos.org/docs/6/html/yum/ Links currently broken.
(Meanwhile see http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/ch-yum.html)
YUM is a command line tool and, despite being extremely powerful, is very easy to use so users new to Linux need not be afraid of it. To use YUM to install software on your system you will need to be root. In it's basic form, YUM uses the following syntax:
So if we wanted to install Firefox, we would do:
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Note that package names are case sensitive and trying to install the package 'Firefox' would result in the message 'Nothing to do'. To find the correct spelling or capitalization, we can use the yum list command to list all matching packages:and you can use YUM to automatically update your system to the latest versions by simply doing:
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Note that if you install software with YUM it will always install the latest version so you do not need to do an update after installing a new package.Using YUM really is that easy.
There is a page with some rather nifty RPM and YUM tips & tricks here:
http://wiki.centos.org/TipsAndTricks/YumAndRPM
See also:
http://wiki.centos.org/PackageManagement/Yum
Groups
Another powerful feature of YUM is the concept of groups of software. This is software related to a task grouped together. For example, suppose you chose not to install support for printing or any office-based software when you installed CentOS. Having to find and install packages we need individually could be time consuming so we can simply choose to install the whole software group.
To see a list of groups, we can do:
(I won't list all the available groups - I'll leave that as an exercise for the reader to try)
and to install a software group, we would do:
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orand we can use groupinfo to return information about packages that make up a particular group:
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RepositoriesAll of the above works fine for installing software that is provided as part of the CentOS system, but what about if you want to install a software package that isn't provided by CentOS? This is where 3rd party repositories come in. A vast amount of software has been packaged and is maintained by the packagers and placed into 3rd party software repositories such that it can be installed using YUM. Please read the Wiki page on repositories here:
http://wiki.centos.org/AdditionalResources/Repositories
RPMForge and ATrpms were two of the larger 3rd party repositories that provided software packages for CentOS. However, rpmforge has been largely unmaintained for about 3 or 4 years at the time of writing (late 2016) and is no longer recommended for use. There have been no security updates published for rpmforge packages in several years and what exists may contain unfixed security vulnerabilities. The situation with ATRpms is similar although with this repo, the mirrors that contain the content are often offline so it's tricky to install anything at all and probably lucky that you cannot since it too suffers the same problems as rpmforge - late or missing updates.
The EPEL repository is generally safe and is now easily installable on all supported CentOS versions by running yum --enablerepo=extras install epel-release as the epel-release package is now in the CentOS 'extras' repo to make life easier.
Other third party yum repositories include, nux-dextop which is the current best source for multimedia packages on CentOS and ELRepo which provides hardware support such as display and network drivers.
However, we need to be careful when enabling 3rd party repositories so that they don't conflict with CentOS packages. For example, they may contain newer versions of software packages that may break your system. For this reason we strongly advise not to update packages provided by CentOS with versions from 3rd party repositories as this may break things. Remember - if you break your system, you get to keep the pieces.
To get around this problem we can use a plugin for YUM called 'priorities'. Priorities allows us to rank repositories from 1 to 99 such that packages installed from a repository with a lower number (higher ranking) will never be overwritten or upgraded by a package from a repository with a higher number (lower ranking). For example, if the CentOS base and updates repositories have a priority of 1 and EPEL has a priority of 10, a package from EPEL will never be able to replace a package from CentOS base or updates.
If you are going to enable 3rd party repositories then it is highly recommended
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that you also install and configure the priorities plugin to manage them.http://wiki.centos.org/PackageManagement/Yum/Priorities
How To Install Viewvc On Centos 7
What if you can't find an RPM package for CentOS / RHELHow To Install Viewvc On Centos 7 1
Are you absolutely sure you've looked everywhere? If you're absolutely sure that an RPM for the software package you want to install doesn't exist then you have a number of options:
1) If there is a Fedora RPM package, then attempting to rebuild the corresponding source RPM package on your CentOS system may be a way to create a working binary RPM package.
2) Consider building your own RPM package. If you package the software yourself then it makes it far easier to handle updates.
3) As an absolute last resort you could compile the package from source. In an rpm-based distribution like CentOS you should avoid compiling from source whenever possible because doing so may break your system and it is highly recommended that you do NOT follow this route. Please read this Wiki article for an explanation as to why: