Ensure that the MCS volume service is configured for the region.

There is a subsystem of MCS known as the volume service, which provides a critical piece of functionality when using MCS with AWS. The volume service has some static pre-configuration stored in the database at the site level. When we ship the product, we pre-seed those configurations with all regions that Amazon are operating at the time. But when new ones come along, the configuration has to be added. Since we fully expected Amazon to introduce new regions at any time, and we don’t want customers to need to wait for a new version of XenApp, we added a powershell cmdlet that allows you to introduce or update the volume service configuration for any region of AWS.

The configuration that is required consists of two pieces of data: the region name and the template ID for Amazon Linux in that region.

The region name is simply the shorthand name of the region that you want to use, such as “us-east-1” or “eu-west-2”. See http://docs.aws.amazon.com/general/latest/gr/rande.html#ec2_region for the full set of regions.

The Amazon Linux template ID is a string of the form “ami-xxxxxx”, and needs to be the correct AMI for EBS-backed Amazon Linux x64 (HVM), which you can look up in this table published by Amazon: https://aws.amazon.com/amazon-linux-ami/ 

To add the required configuration to XenDesktop, do the following from Powershell:-

PS> Add-PSSnapin Citrix.Host.Admin.v2
PS> Set-HypVolumeServiceConfiguration –VolumeServiceConfigurationName SiteDefault –ConnectionType AWS –RegionName eu-west-2 –BaseLinuxTemplateId ami-1234abcd

The RegionName and BaseLinuxTemplateId need to be substituted as per the instructions above, the rest of the command can be copied verbatim.

Ensure that MCS will use Signature v4 when making REST calls to the S3 service.

Some new regions only accept REST API calls that are authorized with Signature v4. Recent versions of XenDesktop have code to enforce this, but 7.6 requires it to be applied via a configuration setting as follows:-

On the DDC, open the file C:\Program Files\Citrix\MachineCreation\Service\Citrix.MachineCreation.exe.config.

Add the following setting to the <appSettings> portion of the XML document:

<add key=”AWS.S3.UseSignatureVersion4” value=”true”/>

Save the file and restart Citrix Machine Creation Service from the service control manager.

Update the host connection configuration options

Finally, there are a couple of product defaults for AWS hosting connections that are out of date in 7.6. The defaults have been upgraded in newer versions, but it is necessary to apply those updates manually in 7.6 when using some of the newer regions.

Procedure as follows:-

1. Launch Citrix Studio
2. In the tree control, select Configuration/Hosting
3. In the main central pane, select your AWS hosting connection
4. In the actions tab on the right-hand side, select Edit Connection
5. In the dialog that appears, select the Advanced tab
6. In the Connection options text box, add the text VolumeWorkerInstanceType=t2.small,UseExplicitVpcForVolumeWorkerBootstrap=true 

There is no need to perform any service restarts after making this change.

Note: If you intend to use AWS dedicated instances for your MCS catalog, then the t2.small instance type cannot be used for the volume worker. This is because Amazon do not permit the T2 series instances to run as dedicated instances. If you wish to use dedicated instance, consider an alternative instance type such as m4.large.