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Virtual Machine and Application Support



Zynstra Cloud Managed Servers include core IT services, delivered as ‘Curated Virtual Machines’ and the ability to deploy additional applications in to ‘Custom Virtual Machines’.

This document explains how these types of VM differ, in terms of configuration options and the support received as part of the Zynstra managed service. It also considers the types of application that can be deployed in to Custom VMs.

Curated VMs

Curated VMs include the core IT services installed on all Zynstra servers and a number of optional add-on applications. Each server comprises nearly twenty Curated VMs running network, security, monitoring, remote management, and file server functions.

A short list of example Curated VMs include the following (with system host names shown in brackets):

  • Microsoft Active Directory (ZDC)
  • Firewall and Web Filtering (ZNETMGR)
  • User and Group File Share (ZFILEMGR)
  • Microsoft Remote Desktop Services Broker (ZRDP)
  • Monitoring (ZMONITOR)
  • Security (ZSECURITY)
  • Backup Processes (ZBKMGR)

In all cases, the Curated VM is purchased and installed as part of the Zynstra solution.

Curated VMs are carefully selected to meet the requirements of all Zynstra customers, and are fully verified, performance-tuned and integrated in to the solution’s system architecture.

The VM, operating system and installation are therefore pre-configured to ensure a simple and consistent deployment of the server. The VM and operating system configurations and the service installation cannot therefore be modified by the IT service provider.

The service configuration, such as firewall rules, file share permissions, and domain controller policies are of course configurable by the IT service provider to meet the unique needs of end-users.

Occasionally, use of a Curated VM may result in a need to modify the host VM’s compute or storage resources. The Zynstra Support Team are able to assist in allocating additional resources to Curated VMs when necessary.

Custom VMs

Custom VMs provide a host running a Linux or Windows Server operating system (OS) image provided as optional add-ons to the Zynstra solution. They are intended to run custom applications such as line-of-business software, databases, and point of sale software.

Custom VM hosts are part of the Zynstra architecture, benefiting from the solution’s hardware virtualization, resilient storage, backup processes and security.

The Custom VM’s operating system is supplied with the Zynstra solution. Unlimited Linux OS licenses are included, while Windows Server licenses are supplied as add-ons to the service.

The Zynstra Support Team will create, modify and delete Custom VMs at the request of the IT service provider.

While the virtualization layer that hosts custom VMs is fully monitored and managed as part of the Zynstra service, the IT service provider manages the payload including installing applications, monitoring applications, updating applications, and updating the OS (to ensure OS patches are compatible with their applications).

Comparing Curated and Custom VM Support   

An important distinction between Curated and Custom VMs is the level of support they receive as part of Zynstra’s managed service.

The following table compares the responsibilities of the Zynstra service and the IT service provider delivering a solution to end users. From the virtualization layer up to the application being hosted, the following roles and responsibilities are assigned:

  • Supplier refers to the party that provides the software image along with any necessary licenses and is responsible for installation on the server.
  • Configuration refers to the operation of the software, such as configuring it to work to meet specific end-user requirements.
  • Management refers to the party that patches, updates and monitors the software on an on-going basis.


System Component

Curated VM

Custom VM

Virtualization Supplier



Virtualization Configuration (CPU/RAM/HDD)



Virtualization Management



OS Supplier



OS Configuration


IT Service Provider

OS Management


IT Service Provider

Application Supplier


IT Service Provider

Application Configuration

IT Service Provider

IT Service Provider

Application Management


IT Service Provider

Applications for Custom VMs

Custom VMs are intended to host business applications and software. Zynstra servers have been shown to offer good performance for a range of different workloads including those biased towards either computation or data processing.

Examples of applications commonly hosted in Custom VMs include:

  • Database systems
  • Accountancy software
  • HR and employee portals
  • Point-of-sale software

Custom VMs are not designed to host infrastructure or network functions, particularly where that function replicates core IT services already delivered as a Curated VM. This is because these sorts of application need to integrate with the other infrastructure and network functions of the Zynstra server which are pre-configured for ease of deployment and reliability.

If you have a requirement to deploy infrastructure or network functions, the Zynstra Support Team should first be contacted so that they can advise you on compatibility.

Examples of infrastructure or network functions that should be discussed with the Zynstra Support Team before deploying in to Custom VMs include:

  • Virtual firewall or web filters (external firewalls and web-filters can be supported)
  • Virtual switches
  • Virtual routers or other broadband termination functions
  • WAN optimisation or other traffic manipulation functions

Virtualization Platform

When deciding how to deploy applications on to a Zynstra server, it can be helpful to have an understanding of the underlying virtualization layers – the hypervisor that host Custom VMs and the file system that ensures storage resilience and performance.

A basic understanding of these components can help ensure application compatibility and assist with the correct sizing of the Custom VM.


The Zynstra hypervisor is based on the Xen Project hypervisor, which is also used widely by cloud-scale, enterprise-grade services such as Amazon EC2, Oracle VM and Citrix XenServer.

The broad adoption of Xen, estimated at over 10 million active users, means the hypervisor it is both widely supported by application vendors and benefits from the testing and improvements contributed by its 2000 commercial partners.

Disk Volume Manager

All VMs hosted by the Xen hypervisor make use of virtualized storage via a Xen disk driver domain. This in turn uses ZFS as the volume manager, virtualizing the server’s physical drives while ensuring data resilience and performance.

ZFS was originally developed by Sun Microsystems for use in their enterprise server range and now is used widely in enterprise-grade storage devices.

By using ZFS as the volume manager, all disk access, including Custom VMs using their own native file systems, benefit from ZFS features:

  • Checksums ensure data written to disk remains correct, avoiding issues caused by ‘bit rot’ and data corruption on disk.
  • Data write-batching and caching mechanisms take advantage of extra system RAM, SSDs and multiple HDDs, accelerating I/O performance.

When considering the resource requirement for a Custom VM, it should be noted that the Zynstra disk volume manager is already allocated system RAM for data caching purposes. Therefore you may find that it is not necessary to assign individual Custom VMs large amounts of RAM to achieve good application performance, if that RAM is used mainly to accelerate disk performance.

Virtual Switch

The Xen hypervisor’s network driver domain uses Open vSwitch (OvS) to support network virtualization.

Open vSwitch is designed to enable massive network automation through programmatic extension, while supporting standard management interfaces and protocols.

Open vSwitch can support numerous network architectures, while the standard features used by all Zynstra servers include support for NIC bridging, dual-node high-availability interconnects, and 802.1Q VLANs.

Its VLAN capabilities provide the option to deploy Custom VMs on to multiple, separate VLANs and also to segregate different types of traffic on the physical LAN, such as separating guest WiFi from the main office network. Custom network architectures should be discussed with the Zynstra Support Team to assist with configuration.


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