Thursday, 16 October 2014

Cloudstack Overview


What is Apache CloudStack?

Apache CloudStack is an open source Infrastructure-as-a-Service platform that manages and orchestrates pools of storage, network, and computer resources to build a public or private IaaS compute cloud.
With CloudStack you can:
  • Set up an on-demand elastic cloud computing service.
  • Allow end-users to provision resources

Cloud Infrastructure Overview

Resources within the cloud are managed as follows:
  • Regions: A collection of one or more geographically proximate zones managed by one or more management servers.
  • Zones: Typically, a zone is equivalent to a single datacenter. A zone consists of one or more pods and secondary storage.
  • Pods: A pod is usually a rack, or row of racks that includes a layer-2 switch and one or more clusters.
  • Clusters: A cluster consists of one or more homogenous hosts and primary storage.
  • Host: A single compute node within a cluster; often a hypervisor.
  • Primary Storage: A storage resource typically provided to a single cluster for the actual running of instance disk images. (Zone-wide primary storage is an option, though not typically used.)
  • Secondary Storage: A zone-wide resource which stores disk templates, ISO images, and snapshots.

About Primary Storage

Primary storage is associated with a cluster or (in KVM and VMware) a zone, and it stores the disk volumes for all the VMs running on hosts.
You can add multiple primary storage servers to a cluster or zone.

About Secondary Storage

Secondary storage stores the following:
  • Templates — OS images that can be used to boot VMs and can include additional configuration information, such as installed applications
  • ISO images — disc images containing data or bootable media for operating systems
  • Disk volume snapshots — saved copies of VM data which can be used for data recovery or to create new templates
The items in secondary storage are available to all hosts in the scope of the secondary storage, which may be defined as per zone or per region.

Networking:-[Ip address allocation]

 When basic networking is used, CloudStack will assign IP addresses based in the CIDR of the pod to the guests in that pod. The administrator must add a Direct IP range on the pod for this purpose. These IPs are in the same VLAN as the hosts.


Thursday, 2 October 2014

Virtualization Hardware drivers and devices

Emulated devices
Emulated devices, sometimes referred to as virtual devices, exist entirely in software. Emulated device drivers are a translation layer between the operating system running on the host (which manages the source device) and the operating systems running on the guests. T he device level instructions directed to and from the emulated device are intercepted and translated by the
hypervisor. Any device of the same type as that being emulated and recognized by the Linux kernel is able to be used as the backing source device for the emulated drivers. 

Para-virtualized Devices
Para-virtualized devices require the installation of device drivers on the guest operating system providing it with an interface to communicate with the hypervisor on the host machine. T his interface is used to allow traditionally intensive tasks such as disk I/O to be performed outside of the virtualized environment. Lowering the overhead inherent in virtualization in this manner is
intended to allow guest operating system performance closer to that expected when running directly on physical hardware.

Physically shared devices
Certain hardware platforms allow virtualized guests to directly access various hardware devices and components. T his process in virtualization is known as passthrough or device assignment. Passthrough allows devices to appear and behave as if they were physically attached to the guest operating system.

Wednesday, 1 October 2014

Vlan Concepts

A VLAN (Virtual LAN) is an attribute that can be applied to network packets. Network packets can be "tagged" into a numbered VLAN. A VLAN is a security feature used to completely isolate network traffic at the switch level. VLANs are completely separate and mutually exclusive. T he Red Hat Enterprise
Virtualization Manager is VLAN aware and able to tag and redirect VLAN traffic, however VLAN implementation requires a switch that supports VLANs.
At the switch level, ports are assigned a VLAN designation.

A switch applies a VLAN tag to traffic originating from a particular port, marking the traffic as part of a VLAN, and ensures that responses carry
the same VLAN tag. A VLAN can extend across multiple switches. VLAN tagged network traffic on a switch is completely undetectable except by machines connected to a port designated with the correct VLAN. A given port can be tagged into multiple VLANs, which allows traffic from multiple VLANs to be sent
to a single port, to be deciphered using software on the machine that receives the traffic.