What is XenServer and how to use it?

What is XenServer and how to use it? post thumbnail image

About XenServer

Citrix XenServer is the complete virtualization platform. XenServer runs directly on server hardware without requiring any Operating System, which results in an efficient and scalable system. XenServer lets us create VMs, take VM disk snapshots and manage VM workloads.  

Benefits of Using XenServer

  • 1. We can build and manage multiple VMs on a single Physical server which reduces the cost of infrastructure.
  • 2. Easy to integrate with existing network and storage infrastructure.
  • 3. Zero time downtime to migrate VMs from one host to another (with Xenmotion).
  • 4. VM availability by configuring High Availability (HA) policies that VM will restart in another host if the current host fails.
  • 5. We can create multiple VMs using templates easily.
  • 6. Can easily schedule a snapshot of VMs.
  • 7. Alarm alerts can help us get a monitor of VMs health. And we can also configure email notifications.
  • 7. To easily Manage XenServer, we can use the XenCenter GUI desktop application.  

CITRIX Hypervisor

XenCenter

XenCenter is a desktop GUI application where we can add/manage our XenServer environment. And deploy new VMs and managing them.  

Connecting host servers and adding them to the list of managed resources in XenCenter.

Creating Storage repositories called SR to provide storage that can be shared between multiple servers.

Manage Servers together using resource pool with shared storage.

Creating new VMs using XenCenter GUI and can build VMs using pre-build templates.

This is the basic GUI of XenCenter desktop application

Manage Servers

We can add, manage, remove our XenServers to XenCenter application and can manage from GUI application.

Server user login credentials are required to add new Server.

Once it is added, we can manage server from this. In this wizard we can configure Storage, Networking, ISO libraries and New VM builds etc.

VM Builds

It is easy to build new VMs with few clicks. For this we required to setup ISO libraries into XenServer where VM will take guest OS image.  

Give a meaningful name for New VM.

Choose ISO image for the VM.

Choose Home server for the new VM. It is require when we have multiple Xenservers added in to XenCenter.

CPU & Memory allocation

Select storage for the VM. We can Add more storage/disk if we think we required.

Choose Network device for the VM.

Review the details you choose and Finish.

Once VM has been created it shows under home server’s list. We can add, change virtual machine’s specifications at anytime.

Note: We can also create and manage VMs through xe CLI.

VM Templates

Template is a master copy of a VM which includes virtual machine’s disks, devices and all VM settings. We can use a single template for multiple times to create new VMs.

Note: We cannot start, stop or login into template once it is created.  

VM Snapshots

VM snapshot is a copy of the state and data of a virtual machine at a specific point of time. We can retrieve a snapshot to virtual machine. XenCenter gives us an option to schedule our snapshots jobs.

We can choose multiple VMs for snapshot schedules.

In addition to save VM’s disk metadata, we can also use Disk and memory snapshot which also save the VM’s memory state (RAM). These snapshots can be useful if we are upgrading or patching software or testing a new application.  

Scheduled Snapshots can set by hourly, daily and weekly basis. The oldest scheduled snapshot will be deleted once the maximum number of snapshots reached.  

We can configure and manage multiple schedule snapshots.

VM Disk Usage and Extension

We will create Volume Groups (VG) for all virtual machines. Volume Groups helps us to increase the storage whenever filesystems utilized maximum space. No down time required for extending filesystem.

Benefits of using LVM

  1.  The main benefit of LVM is that ability to grow the filesystems online.
  2.  No need to move the data from the disk and reformat the storage and then moving back everything for an upgrade.
  3. We can also add new physical storage and then attach with existing Volume Group.
  4. If after extending the partition, you think that space is no more required then we can reduce back to the original size.

Note: We cannot shrink XFS filesystem.

Alarm Alerts

We can set Alarms for CPU, Memory and Network usage in Alerts wizard. It will notify us whenever the resources usage crosses the thresholds. And we can also get these alerts to our Email account by configuring Email Options.

IPTables

We are also planning to implement Iptables in all servers to control network traffic and security. However, this topic is not realted to XenCenter but we can configure iptables in OS level and secure our servers and VMs.

In a simple way, Iptables are a program firewall in Linux that allow users to write specific rules. We can allow, drop and reject the inbound, outbound network and ports.

Benefits:

  1. This is the most reliable software firewall that Linux have.
  2. Versatile control tool for command line.
  3. The concept of this tool is easy to write the rules.

Hosts and Resource Pool

Resource pool enables multiple XenServer hosts bound together into a single managed entity which can host Virtual Machines. When combined with shared storage, a resource pool enables VMs to be started on any XenServer host which has sufficient memory with minimal downtime. If any XenServer host down due to hardware failure then VMs under this host can be restarted in another XenServer host which available in the pool.

If we configure the HA (High Availability) in the resource pool, VMs will automatically move to another XenServer host whenever hardware fails occurs.

Note: Required shared storage to configure HA in resource pool.

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