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Azure Availability Zones with MCS Catalog


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It's worth distinguishing which components you'd want in an Availability Zone:

 

Cloud Connectors / Storefront / NetScalers

These are all persistent servers and within an appropriate Azure region (e.g. West Europe) you can duplicate the services using Availability Zones

Cloud Connector in Zone 0, Cloud Connector in Zone 1, SF in Zone 0, SF in Zone 1, VPX in Zone 0, VPX in Zone 1

So you now have HA of service - if Zone 0 in West Europe falls over, Zone 1 keeps the infra alive

 

So what about the VDAs?

If you have persistent VDAs, then they can be allocated to Zones - tick

If you have non-persistent VDAs then consider the components

 

Master Image VDA (managed or unmanged disk) - the disk can only exist in Local Redundant Storage - therefore it's tied to a zone - you don't know which zone within the region it is located - that zone is susceptible to failure - however you're unlikely to be performing vdisk updates in a DR situation - make sure the Master VM (and assocaited storage is backed up)

 

Managed and Unmanaged disks can only exist in Local Redundant Storage - this is the main limitation

 

The VDAs

The master image VHD is copied to a snapshot - this is LRS, and therefore can only exist in one zone in the region - if that zone goes down, none of the VDAs (even if they are in another Zone can access the snapshot)

 

The VDA identity disks are stored in an LRS storage account - again only in one zone so not regionally redundant

 

The VDA Virtual Machines get deleted at shutdown and restart, so even if you could add them to an Availability Zone - they'd just keep dissapearing from the AZ at shutdown and restart - and of course all the VDAs are dependent on the snapshot which is rooted in a single Zone

 

You'd like to think that you could create multiple catalogs in the region and then aggregate via a Delivery Group - makes sense, however as you cannot choose a Zone within a region when creating a catalog, sod's law tells me that even with a 1 in 3 chance, the two catalogs would probably end up in the same zone

 

If CItrix could sort out AZ options when creating a catalog, we should be able to deploy an HA environment within a single Azure Region usin two catalogs. I'd be happy with two catalogs in two zones, or ideally tag the VDA to a Zone at creation - the second option would still be limited tho' by the single zone LRS placement of the snapshot

 

All the above still hasn't considered profile storage, redirected folders, user data, team data etc

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38 minutes ago, D Gibbs said:

If CItrix could sort out AZ options when creating a catalog, we should be able to deploy an HA environment within a single Azure Region usin two catalogs. I'd be happy with two catalogs in two zones, or ideally tag the VDA to a Zone at creation - the second option would still be limited tho' by the single zone LRS placement of the snapshot

 

All the above still hasn't considered profile storage, redirected folders, user data, team data etc

 

That is my exact ask / want.  I would like to be able to create a MCS catalog that is AZ aware and aggregate via a Delivery Group.  I thought that is what they were announcing in their blog post, but apparently not so much because I cannot find the "preview" of the feature and it is not available yet as of the latest 1912. 

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As James pointed out, the Citrix Article was written in June 2018 when Availability Zones were an Azure Tech Preview feature - not a Citrix Tech Preview feature

 

In terms of VDAs being in availability Zones, Azure VM disks cannot be hosted on Zone Redundant Storage, only Local Redundant Storage, so the MCS snapshot and identity disks are presumably tied to one Zone / local DC within the region (replicated three times)

 

The chances of an Azure Zone/Local DC going down are fairly slim - Microsoft offer 99.95 SLA on LRS storage - they offer 99.99 on ZRS - so on paper we're worring about a tiny probability - probably smaller odds than winning the lottery

 

Only way to get past 99.95% would be a second catalog in a second region - this would still be a 99.99% SLA tho' 

 

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