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Sunday, October 12, 2008

Linux VPS3 - Operating System Level Virtualization Features

The software architecture of operating system-level virtualization is different from traditional virtual machine architecture because it always runs the same operating system (OS) kernel as the host system. It does this while continuing to enable multiple Linux distributions in individual Linux VPS accounts.

This single-kernel implementation technology enables you to run Linux VPS accounts with near-zero overhead. Linux VPS accounts offer an order of magnitude higher efficiency and manageability than traditional virtualization technologies.

Each physical server utilized by Linux VPS is divided into small computational partitions. Each partition operates as a real, physical server. For Unix-like systems, Linux VPS technology is similar to an advanced extension of the standard chroot mechanism.

Operating System-level Virtualization

From the point of view of applications as well as Linux VPS users, each Linux VPS is an independent system. This independence is provided by a virtualization layer in the kernel of the Host OS which is an operating system installed on the Hardware Node (HN), a computer where the Operating System level virtualization is installed for hosting Linux VPS accounts.

Only a small portion of the CPU resources is spent on virtualization (approximately one or two percent). The main features of the virtualization layer implemented in operating system-level virtualization are the following:

Any Linux VPS looks and behaves like a regular Linux system. It has standard startup scripts; software from vendors can run inside a Linux VPS without operating system-level virtualization-specific modifications or adjustment.
A user can change any configuration file and install additional software.
Linux VPS accounts are completely isolated from each other (file system, processes, Inter Process Communication (IPC), sysctl variables).
rocesses belonging to a Linux VPS are scheduled for execution on all available CPUs. Consequently, Linux VPS accounts are not bound to only one CPU and can use all available CPU power.

Network Virtualization

The network virtualization layer isolates Linux VPS accounts from each other and from the physical network:

By default, each Linux VPS has its own IP address. In addition, Linux VPS offers the fee-based option of supporting multiple IP addresses.
At all times, network traffic for one Linux VPS is isolated from the other Linux VPS accounts. In other words, Linux VPS accounts are protected from each other in the way that makes traffic snooping impossible.
Firewalls may be used inside a Linux VPS (the user can create rules limiting access to some services using the canonical iptables tool inside the Linux VPS). In other words, it is possible to set up firewall rules from inside a Linux VPS. In addition, IP tables can offer dynamic Denial of Service (DoS) by means of configurable chain rules
Routing table manipulations and advanced routing features are supported for individual Linux VPS accounts. For example, setting different maximum transmission units (MTUs) for different destinations, specifying different source addresses for different destinations.
IP tables can offer dynamic Denial of Service (DoS) by means of configurable chain rules.

Resource Management

Resource management is important for Linux VPS. Utilization of the resources available on your account is considerably higher than that of typical computer system. Linux VPS resource management controls the amount of resources available to each Linux VPS accounts. The controlled resources include such parameters as CPU power, disk space, and a set of memory-related parameters. Resource management enables your account server to efficiently provide the following functions:

Share available resources among individual accounts.
Maintain a server's part in network Quality of Service (QoS).
Isolate performance and resource isolation.
Protect the server from Denial of Service (DoS) attacks.
Collect usage information for system monitoring.

Skel Package

Technicians pre-configures each Linux VPS account with the following core services residing on the virtual private server account:

Web -- Hypertext Transfer Protocol (HTTP) and HTTPS.
Email -- Simple Mail Transfer Protocol (SMTP), Post Office Protocol (POP), and Internet Message Access Protocol (IMAP).
File Transfer Protocol (FTP)
Shell access tools -- Telnet, Secure Shell (SSH), cron

These core services are managed by support staff, but can be configured by the customer to run according to their specific needs. Our support staff will provide basic instructional support for configuring and using the core services, as well as maintaining the system functionality of these services free of charge. We reserve the right to adjust Linux VPS resources as required to preserve an optimal operating environment for all Linux VPS customers.

By default your new Linux VPS account is pre-configured as a Web and email server. Your account begins as a copy-on-write (COW) image of a technician-tested, basic RHEL installation. However, you can configure your Linux VPS account to provide additional services

Copy-on-Write

Linux VPS fully utilizes the advantages of a Copy-on-Write (COW) file system. As you update and customize the server, Linux VPS continues to use central files maintained by technicians through file system overhead with skel. The COW file system ensures that your server has relatively unfettered access to system resources such as Random Access Memory (RAM). Over time, files which are unique to your own server and configuration can grow in size to suit own your needs.

The COW file system is especially important for virtual memory operating systems; when a process creates a copy of itself, the pages in memory that might be modified by either the process or its copy are then marked copy-on-write. When one process modifies the memory, the operating system's kernel intercepts the operation and copies the memory. It does this so that changes in the memory associated with one process are not visible to any other processes.

The ability to sparsely use memory is an important advantage of the COW file system. This advantage is because the usage of physical memory only increases as data are stored in physical memory. And this enables efficient hash tables to be implemented. The hash tables use only a little more physical memory than necessary to store the objects they contain.

RPM

Your Linux VPS account supports RPM, an open packaging system for Linux and UNIX systems distributed under the terms of the GPL. The package maintains a database of installed packages and their files. This enables you to maintain and upgrade your account configurations and customizations with minimal risk of losing them as you do so.

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