In the first part of this blog series we looked at specific details on Citrix Delivery Center and the Disaster Recovery demonstration for SAP NetWeaver. In this posting we will cover different High Availability solutions also demonstrated at SAP. In addition to this blog series, please refer the Reference Architecture document that provides all the technical details about Citrix and Marathon solutions implemented for SAP.

Getting back to High Availability, Citrix XenServer and Marathon Technologies everRun VM for XenServer provide solutions that covers a broad spectrum of High Availability requirements  ranging from maintenance to complete system-level fault tolerance. Given the breadth of High Availability solutions, IT administrators are bound to find a Citrix XenServer High Availability solution to meet their application availability needs.  

When looking for an HA solution, various factors such as application criticality and business impact must be considered before choosing a particular solution for an application. A more detailed report on determining availability requirements can be found here.  
In our Proof Of Concept environment at SAP, we showcased all levels of High Availability offered by XenServer and everRun VM. First let's look at the out-of-the-box High Availability solutions that XenServer alone delivers:

• XenMotion: XenMotion supports live migration of running virtual machines from one XenServer to another. The primary purpose of XenMotion is to prepare for planned server maintenance.  The end user will not experience any interruption in application performance in XenMotion.
• XenServer High Availability (HA) - Level 1: XenServer HA provides High Availability by automatically restarting failed virtual machines on a different XenServer host within the same resource pool.  The end user will experience an interruption in service as the virtual machine restarts.

In addition, Marathon Technologies everRun VM for XenServer provides High and Continuous Availability for critical virtual machines hosting business applications like SAP NetWeaver Portal:

• everRun VM for XenServer-- Level 2: Marathon Technologies everRun VM Level 2 delivers High Availability from component-level fault tolerance, eliminating downtime caused by I/O component failures and guaranteeing recovery from system failures. The solution identifies faulty I/O pathways before they become a problem and responds to a wide range of I/O and component failures. Active validation of all components on primary and secondary hosts ensures smooth recovery following any primary host component failure.  
• everRun VM for XenServer - Level 3: Marathon Technologies everRun VM Level 3 provides Continuous Availability from system-level fault tolerance, eliminating data loss, downtime and transaction loss. It offers all of the benefits of Level 2 and adds two important attributes:
  a.    Zero downtime, even with complete XenServer host failure.
  b.    Preservation of application and memory states during failure.

The following video features the Marathon everRun VM Level 3 High Availability solution demonstrated at SAP Co-Innovation Labs, Palo Alto. Again, for more technical details on the implementation, please take a look at the Reference Architecture.

When we talk about the Citrix Delivery Center, we are talking about an end-to-end application delivery infrastructure solution. A solution which represents a family of Citrix product lines: Citrix XenServer, Citrix XenApp, Citrix NetScaler and Citrix XenDesktop. It also represents products that add integrated security, management and networking functions, products such as: Citrix Access Gateway, Citrix Branch Repeater and Citrix Desktop Receiver. Overall, the Citrix Delivery Center gives customers the power to adopt virtualization that meets their specific requirements. Customers can choose to optimize delivery of their Web Applications, Windows Applications, Desktop Delivery, Data Center Optimization - individually or in combination. How about all of them?

Now according to a recent Forrester study "49% of enterprises surveyed that are implementing or interested in virtualization solutions indicate that improving disaster recovery/business continuity continues to be a very important motivation for adoption". So what better way to pique their virtualization/business continuity interest than by demonstrating an end-to-end Citrix and Marathon combined solution onsite at the world's largest business software company SAP.
Recently the Citrix Worldwide Consulting Solutions and Business Development teams did just that. We built and demonstrated a Proof of Concept environment that delivered a highly available and virtualized SAP infrastructure using a complete Citrix Delivery Center solution. Within a two week period, the Citrix, Marathon, and SAP teams built and demonstrated a complete Proof of Concept environment. For a quick project overview please refer the data sheet here.

So how did we do it....First we virtualized every Citrix Delivery Center component and the backend SAP NetWeaver application servers using Citrix XenServer. Then we showcased what a remote SAP NetWeaver user would experience accessing the SAP NetWeaver Portal via Citrix Delivery Center while focusing on the high availability/fault tolerant solutions Citrix and Marathon provide. Finally, we simulated a complete failure in the primary site and used the combined NetScaler Global Server Load Balancing feature in conjunction with Marathon's everRun DR product to failover SAP to a secondary data center.

Let's go through the steps that describe the demonstrated user experience:

• Remote SAP NetWeaver Portal user securely connects to the SSL VPN provided by Citrix Access Gateway Enterprise Edition.
• All connections from the remote user client are accelerated using Citrix Branch Repeater Plug-in.
• Remote user is seamlessly presented with the Citrix Web Interface website with on-demand access to virtual desktops, applications, bookmarks and other corporate resources.
• From the Citrix Web Interface page, the remote user launches a virtual Windows XP desktop hosted by Citrix XenDesktop. This desktop is a private virtual image of Windows XP running within a secure data center and maintained from a centralized Windows XP image provisioned dynamically with Citrix Provisioning Server.
• From the secure virtual Windows XP desktop, the remote user launches a published SAP NetWeaver Portal delivered by Citrix XenApp. The published NetWeaver Portal application is separated from the virtual Windows XP Operating System allowing optimal user performance.
• As the remote user navigates the application, all SAP NetWeaver Portal connections pass through a Citrix NetScaler configured to optimize SAP NetWeaver Portal application delivery.

We also demonstrated the following high availability and recoverability solutions provided by Citrix XenServer and Marathon everRun software:

• Level 1: XenServer delivers out-of-the-box high availability, including cost-effective core failover, recovery and restart capabilities for SAP applications running in the virtual environment.
• Level 2: Marathon everRun VM delivers high availability of component-level fault tolerance, eliminating downtime caused by I/O component failures and guaranteeing recovery from system failures.
• Level 3: Marathon everRun VM's Lockstep Technology delivers continuous availability from system-level fault tolerance, eliminating data loss, downtime and transaction loss.
• Disaster Recovery: Marathon everRun DR provides a robust and flexible remote disaster recovery solution providing automated and reliable long-distance protection for critical data and applications, in this case, SAP.

Each piece of the demonstration was broken down into small video segments for this blog. The first video features the Citrix Delivery Center environment for SAP from top to bottom including the remote user login, virtual desktop access, and SAP NetWeaver Portal launch. Then a complete site failure is simulated and the secondary site recovery is shown using Marathon's everRun DR solution with Citrix NetScaler's Global Server Load Balancing feature.

Stay tuned for a detailed reference architecture and video blogs on different High Availability scenarios including everRun VM also demonstrated at SAP Co-Innovation Lab.

Here's the video: