OpenVZ Interview Questions And Answers

To configure VPN inside a container first the steps to setup the tun/tap device module has to be followed then VPN has to be installed to work with the tun/tap module inside the container. VPN uses other softwares like OpenVpn, Tinc, etc. to be used to start working with the networking module. After configuring VPN setup the host operating system for communication purpose. VPN continer has to configure VETH interface before the use. NAT can be used as interconnection to configure and use the VPN inside a container.

The commands that are required to manage OpenVZ are as follows:
To show a list of all running VPSs we require a command named vzlist that list the containers and its parameters. The command that is used with it is: vzlist -a
the commands can have many parameters like -o that displays only specified parameters with the name.
To calculate the usage for each container's resources a command named vzcalc is used that show all the shared host system resources that is used by a particular container. -v is the parameter that is used to show only the valid containers that are currently in use.

• OpenVZ is not flexible to provide the services that are being provided by other virtualization platforms.
• OpenVZ is partial virtualization and act as a containerization, whereas other virtualization technologies are either type1 or type2 Hypervisors.
• OpenVZ uses kernel patches to run only Linux operating system, whereas other virtualization platforms can run more than one operating systems.
• OpenVZ is fast and efficient compared to other virtualization technologies.

OpenVZ is also known as Open virtualization is an operating system level platform that is based on Linux kernel and can run system that is based on Linux architecture. It can run multiple Linux system instances in what is called as containers. It contains Linux base operating system and gives very high performance compared to standalone servers. OpenVZ is free to use and imply. It provides custom level kernel to provide the support for its containers and user level tools.

The container consists of:
• Files that consist of system libraries and applications that provides programmers to write the code without looking further. It provides virtualized files as well that keeps the virtualization for the user.
• Users and groups: it consists of isolated root user that allow user to group other users and set the permissions individually or either as groups.

• Process tree: consists of processes that contain other processes under it. The level start from init and it goes as the each process is added.

• Network: consists of the configuration for virtual network devices and the entire container to have its own IP addresses for communication with other devices.

• Devices: consists of access permissions that are used to connect it with the real devices like network interfaces, serial ports, parallel ports, etc.

• IPC objects: consists of the files that are used for inter process communication like shared memory, semaphore, etc.

To over-commit the memory in OpenVZ few pages has to be modified like vmguarpages and oomguarpages that provides the resource management configuration files. Out of these vmguarpages provides the maxium memory a container can have and oomguarpages provides the maximum memory that is being consumed by the processes. These are used to set the limit. Limit also has some files like privvmpages that puts an upper limit on container memory. It is also used for non-swappable kernel memory. By using these functions over-commitment of the memory can be done by using OpenVZ.

Veth stands for virtual ethernet device and it is used as an ethernet device in OpenVZ. It is used inside a container and veth consists of MAC address. Veth uses bridged connection configurations with other devices to setup the networking between the two parties for the communication. It includes IPs and gateways to successfully setup the networking interface. This ethernet device contains two ports one is called as CT0 and another is CT. they are connected with each other and they work as interconnected device such that one's input is another's output.

OpenVZ is a operating system level virtualization platform and provides features like:
• Scalability: this consists of configuration related to hardware like CPU, RAM etc.
• Performance: this consists of performance related issues that are very few in OpenVZ and it reduces the overhead that is being associated with other virtualization platforms
• Density: provides the decrease of overhead that is required by the container and doesn't allow the demands to exceed the physical availability of the resources.
• Mass management: provides administrator rights to use the physical server of OpenVZ so that user can see all the processes that are running on the system and the containers that are consisting inside the OpenVZ

OpenVZ uses tun/tap network module to configure a container. To setup the container using tun/tap device:
• Check your system and see that tun/tap module is already being installed. Use the command to find out:
lsmod | grep tun
• If not present then use the command to load the tun module:
modprobe tun
• Edit the modules.conf that is inside /etc/ to allow the tun module to run automatically during the start of the system.
• set the permission for the container to use the tun/tap module
• the following command allows the container to be set with the permission for the use of tun/tap networking module:
vzctl set 101 --devnodes net/tun:rw –save

OpenVZ utilizes the processing power to reduce the overhead by decreasing the load that is given on a system. It provides better methods to improve the handling of peak loads. It also reduces the complexity by providing standardized and centralized management of the server from one place. It provides a way to isolate the servers from the actual hardware. It uses high-end servers by isolating the server from hardware and with the servers bring added advantages like reliability, longer lifespan, etc.

OpenVZ resource management consists of four components: two-level disk quota, fair CPU scheduler, disk I/O scheduler, and user beancounters. These resources can be changed during container run time, eliminating the need to reboot.

Two-level disk quota

Each container can have its own disk quotas, measured in terms of disk blocks and inodes (roughly number of files). Within the container, it is possible to use standard tools to set UNIX per-user and per-group disk quotas.
CPU scheduler

The CPU scheduler in OpenVZ is a two-level implementation of fair-share scheduling strategy.

On the first level, the scheduler decides which container it is to give the CPU time slice to, based on per-container cpuunits values. On the second level the standard Linux scheduler decides which process to run in that container, using standard Linux process priorities.

It is possible to set different values for the CPUs in each container. Real CPU time will be distributed proportionally to these values.

In addition to the above, OpenVZ provides ways to:

set strict CPU limits, such as 10% of a total CPU time
limit number of CPU cores available to container
bind a container to a specific set of CPUs