As someone who has passed (and failed) several Red Hat exams, I can tell what it takes to achieve the long yearned (?) certification: lots of
luck practice. Really a lot of practice, and this post goes about getting that practice.
First of all, because of the NDA you sign when you take any Red Hat exam, you cannot speak about specifics of the exam tasks. You can, however, talk about the exam objectives, which in the case of the EX200 and EX300 (the most popular, as they give the RHCSA and RHCE certifications respectively) are available here:
Before you start practicing, find out what is the OS version that the exam is going to be based on. It won’t help you much to practice Network Teaming or Firewalld (RHEL7 features) if at the time of the exam you find out it’s based on RHEL6. The practice environment that I’m going to describe is based on CentOS7, so it’s compatible with a RHEL7 based exam.
In order to execute all of the exam objectives, we’ll be creating the following virtual infrastructure:
So in detail, we are going to:
- Create an internal virtual network to interconnect the practice virtual machines without interfering with the host’s public network, nor having direct internet access.
- Create a server that will automatically provide the following network services:
- DHCP: Will provide IP addresses from 10.11.1.100 to 10.11.1.109 for the “labo” machines.
- DNS: Will provide direct and reverse name resolution for the example.com zone (the VMs mentioned on the previous bullet).
- Kerberos: A master server ready to be used for user and services authentication, such as NFS.
- LDAP: This service will provide pre-configured user and groups information to the “dc=example,dc=com” DN.
- Yum: The iso image that I’m using to install the server will stay mounted and available as a yum repository to install the OS and additional packages on the “labo” servers.
- PXE: And the best of all, the server machine will be configured as a PXE server, so you can build and rebuild the labo machines automatically with an included basic kickstart.
An additional note about the items above. Knowing how to configure a Kerberos, DHCP or LDAP is very valuable, but trust me, if it is not an objective of the exam that you’re taking (and it’s not on the EX200 and EX300), you better stay away from it and concentrate exclusively on the exam objectives. That is why this process will take care of this tasks automatically through the provided kickstart, so that you don’t waste time configuring the basics. Additionally, this process allows you to rebuild the environment as many times as you need, leaving it always on the same starting point.
Note that the requirements to run this environment on the physical host are:
- At least 3GB of memory, one for each vm, one for the host (you won’t actually be using all that, but it’s a good practice)
- A CPU that supports virtualization (look for the VT-x or AMD-V flags on Intel and AMD respectively), and make sure that you have this feature enabled on BIOS. For example, on an Intel machine:
virthost[/root]# lscpu | grep Virtualization Virtualization: VT-x virthost[/root]#
Now, assuming that you’re starting almost from scratch and only have one single CentOS/RHEL 6 or 7 machine, this is the process to get you ready to start practicing:
- Install the virtualization platform:
virthost[/opt/centos7]# yum group install "Virtualization Host"
- Start libvirtd:
virthost[/opt/centos7]# systemctl enable libvirtd ln -s '/usr/lib/systemd/system/libvirtd.service' '/etc/systemd/system/multi-user.target.wants/libvirtd.service' virthost[/opt/centos7]# systemctl enable libvirt-guests ln -s '/usr/lib/systemd/system/libvirt-guests.service' '/etc/systemd/system/multi-user.target.wants/libvirt-guests.service' virthost[/opt/centos7]# systemctl start libvirtd virthost[/opt/centos7]#
Note that libvirtd started, by default, a bridge called virbr0:
virthost[/opt/centos7]# ip addr show virbr0 27: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP link/ether 52:54:00:12:a4:47 brd ff:ff:ff:ff:ff:ff inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0 valid_lft forever preferred_lft forever
This network connects the virtual machines with the host’s public network, so we don’t want to use it on our isolated lab environment.
- Download the CentOS7 image from here, and save it to /opt/centos7
- Download the tar file that contains the kickstart, virtual machines and network definition files from here, and extract to /opt/centos7. When you’re done, you should have these files:
virthost[/opt/centos7]# wget -q -O Example.tgz http://bit.ly/1F4dnkR virthost[/opt/centos7]# tar -xzf Example.tgz virthost[/opt/centos7]# ll total 4209696 -rw-r--r--. 1 root root 4310695936 Apr 20 16:01 CentOS-7-x86_64-DVD-1503-01.iso -rw-r--r--. 1 root root 215 Apr 20 16:00 internal.xml -rw-r--r--. 1 root root 2355 Apr 20 18:59 labo100.xml -rw-r--r--. 1 root root 16360 Apr 23 15:57 server.ks -rw-r--r--. 1 root root 2941 Apr 20 16:13 server.xml virthost[/opt/centos7]#
- Create the internal network, where server.example.com will provide the basic services:
virthost[/opt/centos7]# cat ./internal.xml <network> <name>internal</name> <bridge name='virbr1' stp='on' delay='0' /> <mac address='52:54:00:05:4e:d3'/> <domain name='internal'/> <ip address='10.11.1.1' netmask='255.255.255.0'></ip> </network> virthost[/opt/centos7]# virsh net-define ./internal.xml Network internal defined from ./internal.xml virthost[/opt/centos7]# virsh net-autostart internal Network internal marked as autostarted virthost[/opt/centos7]# virsh net-start internal Network internal started virthost[/opt/centos7]# ip addr show virbr1 72: virbr1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP link/ether 52:54:00:05:4e:d3 brd ff:ff:ff:ff:ff:ff inet 10.11.1.1/24 brd 10.11.1.255 scope global virbr1 valid_lft forever preferred_lft forever
- In the same way, define the server and at least a labo machine from the provided xml files. Then to create other lab environments, you can clone them on virt-manager.
virthost[/opt/centos7]# virsh define ./server.xml Domain server defined from ./server.xml virthost[/opt/centos7]# virsh define ./labo100.xml Domain labo100 defined from ./labo100.xml
- You also have to create the hard drive files of those machines:
virthost[/opt/centos7]# qemu-img create -f raw /var/lib/libvirt/images/server.img 10G Formatting '/var/lib/libvirt/images/server.img', fmt=raw size=10737418240 virthost[/opt/centos7]# qemu-img create -f raw /var/lib/libvirt/images/labo100.img 10G Formatting '/var/lib/libvirt/images/labo100.img', fmt=raw size=10737418240
- Export /opt/centos7, so that Anaconda can use it to install the server through the provided kickstart file:
virthost[/opt/centos7]# cat /etc/exports /opt/centos7 *(ro) virthost[/opt/centos7]# virthost[/opt/centos7]# systemctl start nfs virthost[/opt/centos7]# exportfs -a
- And finally, on virt-manager, power up the server and “Run” the server booting from the iso. At the boot menu, modify the entry that reads “Install CentOS7” so that it points to the kickstart:
Hit enter and let the kickstart do its magic. Few minutes later it will reboot. When you see the prompt, you can start installing lab environments.
- So, to deploy the OS on the previously defined lab machine, do “virsh start” or start it from virt-manager, and let it boot from its network interface. You should get this menu:
That’s all! Now you can practice all of the exam objectives. Remember that to reinstall a lab machine, you just need to boot from the network interface.
To reinstall the server, start from step 9 on this process, or, alternatively, create a snapshot or copy the server’s hard drive, for example, using virt-sparsify (VM needs to be down):
virthost[/opt/centos7]$ virt-sparsify -q /var/lib/libvirt/images/server.img /var/lib/libvirt/images/server_clean.img virthost[/opt/centos7]$ ll -h /var/lib/libvirt/images/server.img /var/lib/libvirt/images/server_clean.img -rw-r--r--. 1 root root 10G May 28 14:39 /var/lib/libvirt/images/server_clean.img -rw-r--r--. 1 qemu qemu 10G May 28 09:06 /var/lib/libvirt/images/server.img virthost[/opt/centos7]$ du -sh /var/lib/libvirt/images/server.img /var/lib/libvirt/images/server_clean.img 1.3G /var/lib/libvirt/images/server.img 1.1G /var/lib/libvirt/images/server_clean.img virthost[/opt/centos7]$
Then when needed, copy the “server_clean.img” as “server.img” and power on the VM again. As simple as that. In case you’re wondering, all of the passwords are provided as clear text on the kickstart files.
Finally, some recommendations on objectives that you should practice on the labo machine:
- Configure a yum repository pointing to http://server.example.com/pub/centos7/repo/
- Add a network card and configure nic teaming/bonding
- Configure user authentication using LDAP y Kerberos
- Restrict access to lab using firewalld (or iptables)
- Share directories from server using NFS and/or Samba y secure them using Kerberos
- And anything else on the exam objectives list!
Good luck on your exams, and let me know if you have any question.