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Thursday, June 11, 2015

Citrix and SQL always On Designs.

Image result for pros and consChris Hahn put together a quick PROs & CONs list to using SQL Always On for Citrix instead of SQL mirroring.


A lot of clients have been asking about SQL Always On with new Citrix designs.  A couple points on the PROs / CONs vs. SQL mirroring.

  • Don’t have to set mirror database configuration on clients.
  • Not applicable for Citrix yet, but Always On supports reading the DB from any node of the Availability group.  With SQL Mirroring you can only read from active node.
  • Faster failover than mirroring, if SQL nodes are in single subnet.

  • Requires Enterprise Edition which is much more expensive than the Standard edition required for Mirroring.
  • If you are failing over across sites / subnets, failover times will probably be slower than mirroring.  If the application supports the multi-subnet failover SQL connection string, then both subnet IPs register in DNS and the app attempts connection to all IPs in parallel for the fastest failover times.  Very few apps support this though, so the legacy mode is to not register all IPs in DNS, and have clustering change IP at failover.  Then you have to wait for DNS changes to propagate during a failover.  This is much slower than failover with traditional mirroring.
  • Not all applications support Always On, particularly the multi-subnet failover option.  Mirroring has been around for a long time and has much broader support.

Some additional information related to the subject can be found here:

Multi-Subnet failover connection string can be configured for XenDesktop Databases and there is a handy script to configure this -
http://blogs.citrix.com/2014/10/29/updating-database-connection-strings-in-xendesktop-7-x/

Multi-Subnet failover option is still not supported for PVS -
http://discussions.citrix.com/topic/337030-pvs-7-on-sql-2012-always-on-a-supported-citrix-deployment/

SQL connection timeouts
http://blogs.msdn.com/b/alwaysonpro/archive/2014/06/03/connection-timeouts-in-multi-subnet-availability-group.aspx

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Wednesday, May 20, 2015

Document Starter: Deploying an Application / Desktop

Sometimes you just need a little help creating documents.  Just a starting point to really get the juices going and head start to get the documentation ball rolling.  Aaron Silber has a nice starter document for anyone looking to document their XenApp/XenDesktop groups.

You can download the actual Word Document here: <ShareFile Location Here>


This document will detail the steps necessary to deploy an application or desktop to users via StoreFront or the Receiver. At a high level, the process is broken down into two steps,

  • Creating a Machine Catalog, which is a collection of desktops or physical computers that are managed as a single entity.
  • Once the catalog has been created, the administrator assigns applications from the machine catalog to users via delivery groups.

In the new world of XenApp/XenDesktop v7.x, in order to publish an application, you create and add applications in the Citrix Studio and make them available to Delivery Group Users. Create Delivery Groups for specific teams, departments, or types of users. Delivery groups specify the groups of users who access desktops or applications. Users can be members of multiple delivery groups to enable various access to applications and / or desktops.

Creating a Machine Catalog

Launch the Citrix Studio Console

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Select Machine Catalog

 

Right click and select Create Machine Catalog

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Click Next

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Select Windows Server OS

 

Click Next

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Select Another service or technology

 

Click Next

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Select the computer accounts to be part of this machine catalog.

 

Click Add Computers

 

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Enter in the Computer Name

 

Click Next

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Fill in a Machine Catalog Name and optionally a description for administrators to see.

 

Click Finish

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End of Machine Catalog Creation

Creating Delivery Group

Click on the node called Delivery Groups

 

Right-Click and select Create Delivery Group

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Click Next

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Select a machine Catalog to be used to publish the applications to.

 

Increase the number of machines to the amount of machines that should be made available to this group.

 

Click Next

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Select Desktops and applications

 

Click Next

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Click Add users, to add in users and/or groups

 

Click Next

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XenApp will automatically scan the server for applications and display them for easy publishing.

 

If you want to customize an application, click it and select the Application Properties button for more details.

 

Click Next

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Click Next

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Enter in a Group name and a Display name.

 

Click Finish

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End of Delivery Group Creation

You should now be able to log into a StoreFront server and access the application(s) / Desktop(s) that were just configured.

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Friday, May 15, 2015

PSA: VENOM Exploit on Citrix XenServer

I’ve had some clients ask about a new exploit making it’s way around security desks lately.  It’s called VENOM and it leverages a buffer overrun scenario that has been detected in certain code used to process commands from a Virtual Floppy controller on a VM to gain unauthorized access across the entire HOST and all VMs running within it. VENOM exploits the hypervisors specifically to gain unauthorized access to additional Virtual Machines running on the host platform.

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After some research, it looks as though this is primarily an issue with the QEMU floppy controller code found in some open source Hypervisors including Citrix’s XenServer. 

VMware and Hyper-V are not known to be affected by this exploit.

EDIT: As of this post, Citrix has not issued patches for XenServer but AND has opened up a KB article to track the progress of the exploit.  (http://support.citrix.com/article/CTX201078)

This is also a good time to discuss whether it makes sense to even have Virtual Floppy Drives on VMs.  It’s such a legacy thing and is typically a default configuration setting for new VMs.  It might be worth looking at your templates to see if there are any unnecessary devices that should be removed to avoid future exploits.

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Thursday, April 9, 2015

Come see Sam Jacobs talk StoreFront at Citrix Synergy!

imageIf you have had a Web Interface, Netscaler or Storefront issue and took it to the Citrix Forums, there’s a good chance Sam Jacobs (@WIGuru) has helped you sort it out!  For the second year in a row, Sam has landed a coveted spot at Citrix Synergy to share his deep knowledge on bending Citrix technologies to his will.  ;)  (BTW: Last year was standing room only for BOTH sessions so if you are going to be at Synergy, pre-register for the session to get a seat!)

Here is Sam’s official Promo announcement with all the details:

Making a Splash with Storefront – A Deep Dive!

It’s official! StoreFront is here to stay so let’s ensure StoreFront servers are production-ready through solid documentation. Documentation is essential because is allows you to:

- Clone a StoreFront server group,
- Help troubleshoot any issues with the deployment, and
- Re-create servers after a crash.

Dive deep with me during my session at Citrix Synergy, where you will see how easy it is to automagically generate awesome StoreFront documentation (in MS Word or PDF format) using the StoreFront PowerShell SDK. You will learn which PowerShell cmdlets are used to document a StoreFront server group (there are also complementary cmdlets with which you can create/modify your server group).

Plus, the techniques you will learn in this session are not limited to StoreFront! You will learn how to create an intuitive GUI for your PowerShell scripts that can modify itself based upon variables in the script. You will also learn how to add custom icons and graphics to the forms used in your scripts.

As usual, all source code for the session customizations will be made available to presentation attendees.
[Be sure to subscribe for all updates!]

So join me at Citrix Synergy for SYN417: StoreFront PowerShell documentation deep dive, on Tuesday, May 12 from 4:00-4:45 PM PST in Valencia Ballroom D. Let me show you how to produce awesome StoreFront documentation, and become more proficient in PowerShell in the process. Hope to see you there!

Sam Jacobs is IPM’s Director of Technology Development Services. With more than 25 years of IT consulting, Sam is a Citrix StoreFront, Web Interface and Netscaler customizations and integrations expert. He holds Microsoft MCSD and Citrix Netscaler certifications, is the author of IPM’s TechDev blog and is an active Citrix Forum contributor. A seasoned technical speaker, Sam integrates industry insight with real implementation experience, and has presented customizations at Synergy and BriForum.

Learn more about
IPM or the TechDev practice.
Sam can be reached at:
sjacobs@ipm.com.

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Friday, March 6, 2015

Is your Citrix Netscaler vulnerable to the FREAK Attack?

Man in the MiddleI have heard this asked before and thought it would make a good post to get some information out.

The FREAK (Factoring RSA Export Keys) attack is the latest threat to exploit vulnerabilities in the OpenSSL libraries. You might remember the HeartBleed bug from last year.

FREAK (formally known as CVE-2015-0204) affects versions of OpenSSL prior to 1.0.1i (released January 15, 2015).  It’s a man in the middle type of attack and affects a lot of different devices.  The official description is here and a good editorialized version here.

I searched and searched but couldn't really find anything official from Citrix on the KBs.  I did run across an old Citrix Forum post related to the Heartbleed bug that stated Netscalers do not use OpenSSL on the internet facing side and therefore would not be affected by internet based OpenSSL attacks.  They actually use an internal SSL stack that they privately test against any known SSL threats.  OpenSSL is only used for connections to the management side.  The information is from a Netscaler Product Manager and can be found here.

It’s a good bet that Citrix engineers are busy testing the internal code stack against the new CVE-2015-0204 vulnerability. Once complete, I am sure will release a KB article like they did with Heartbleed but until then, this will have to do. :) 

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