In this blog, we will share an overview of OpenVZ Virtualization.
What is OpenVZ Virtualization ?
OpenVZ Virtualization is an operating-system level server technology that’s actually based on the Linux kernel and OS.
OS level virtualization means many basic components exist once on the machine, and are used by all guests (like the identical kernel). That means that each container shares the same underlying OS but still operates as secure, isolated Linux container.
Each container performs and executes exactly like a stand-alone server; a container can be rebooted independently and have root access, users, IP addresses, memory, processes, files, applications, system libraries and configuration files. This way you use the resources more efficient
OpenVz is is a linux based virtualization platform, it can only run linux based operating systems such as Centos, Fedora, Debian…etc
One disadvantage of OpenVZ Virtualization is, users are not able to do any kernel modifications. All virtual servers have to get along with the kernel version the host runs on.
It is actually requires both the host and guest OS to be running Linux. Because OpenVZ uses a single patche Linux kernel, but since it doesn’t have the overhead accompanied with legitimate hypervisors it’s super-fast and extremely efficient.
However because it doesn’t have the overhead of a true hypervisor it is very fast and efficient.
Pros
* Container style virtualization, shared kernel with the host-Better pricing since provider can oversell
* A little bit better performance to KVM, since there is no additional virtualization layer between the host and your VPS,which means that there is basically no overhead on assigned CPU, memory and disk resources
* A very low memory footprint, since the OS shares the kernel with the OS. This makes OpenVZ a great choice for VPSes with a low amount of memory
* OpenVZ is usually a good choice for anyone that don’t have special requirements-Less overhead
Cons
* OS templates only, there is no option to manual install your OS
* Not complete virtualization; all operating systems share one kernel.
* Not all kernel modules available.
* As with all virtualization techniques, the CPU and network port are shared, which are shared among all VPSes on this node.
Basic operations in OpenVZ environment
Here CTID representing the ID of a container (VPS – Virtual Private Server).
1. Command to list the running VPSs in a node
#vzlist
Example:-
# vzlist
CTID NPROC STATUS IP_ADDR HOSTNAME
116 114 running xx.xx.xx.xx serverx.test.com
127 46 running xx.xx.xx.xx servery.test.com
138 83 running xx.xx.xx.xx serverz.test.com
129 86 running xx.xx.xx.xx serverq.test.com
2. Command to list running and stopped VPSs in an node
#vzlist -a
Example:-
#vzlist -a
CTID NPROC STATUS IP_ADDR HOSTNAME
116 114 running xx.xx.xx.xx serverx.test1.com
127 46 running xx.xx.xx.xx servery.test2.com
138 83 running xx.xx.xx.xx serverz.test3.com
129 86 running xx.xx.xx.xx serverp.test4.com
110 – stopped xx.xx.xx.xx serverq.test5.com
3. To start a VPS
# vzctl start CTID
Example:-
# vzctl start 120
4. To stop or shutdown a VPS
# vzctl stop CTID
Example:-
# vzctl stop 120
5. To view the status of a VPS
# vzctl status CTID
Example:-
# vzctl status 120
CTID 116 exist unmounted down
6. To restart a VPS
# vzctl restart CTID
Example:-
# vzctl restart 120
7. Creating a container in node
# vzctl create CTID –ostemplate osname
# vzctl set CTID –ipadd x.x.x.x –save
Here CTID is the numeric ID for the container; osname is the name of the OS template for the container , x.x.x.x is the IP address to be assigned to the container.
8.To enter a VPS
# vzctl enter CTID
Example:-
# vzctl enter 126
entered into CT 126
9. Delete a container
# vzctl destroy CTID
10. Suspending a container
# vzctl suspend CTID
11. Set hostname for a Server
# vzctl set CTID –hostname New_hostname –save
12. Add new IP to VPS
# vzctl set CTID –ipadd xx.xx.xx.xx –save
13. Delete IP from VPS
# vzctl set CTID –ipdel xx.xx.xx.xx –save
14. Reset root password of a VPS
#vzctl set CTID –userpasswd root:new_password –save
15. To add NameServer IPs to VPS
#vzctl set CTID –nameserver xx.xx.xx.xx –save
16. Executes commands for a container from node
# vzctl exec CTID command
Example:-
# vzctl exec 120 df -h
# vzctl exec 131 df -h
Filesystem Size Used Avail Use% Mounted on
/dev/simfs 120G 70G 50G 78% /
none 8.0G 4.0K 8.0G 1% /dev
none 8.0G 0 8.0G 0% /dev/shm
17. To check the resource usages
# vzcalc -v CTID
Example:-
# vzcalc -v 110
# vzcalc -v 121
Resource Current(%) Promised(%) Max(%)
Low Mem 1.28 17897827062.42 182706895112.42
Total RAM 33.79 n/a n/a
Mem + Swap 1.73 38695649865149.61 n/a
Alloc. Mem 2.95 38695649865149.61 38695649865149.61
Num. Proc 0.07 n/a 2395786836523892.00
——————————————–
Memory 35.79 38695649865149.61 2395786836523892.00
