What are the steps for having high availability in Xenapp ?
what is the architecture for Xenapp high Availability ?
Describe how we can implement High Availability in Xenapp without using third party software ie. marathon technologies ?
How can we manage 30 citrix server in four different farms? (Hogh Availability)
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High Availability can mean a lot of things and you can also go over board with HA, but that depends on how critical and how much money you're willing to throw at it.
Are you talking Local HA (i.e. making sure each XenApp component in one location can't cause an outage)?
Are you talking about Geographic HA (i.e. making sure if a location completely fails you can bring it up at the second site)?
I'll break it down into components for a single location.
1. Web Interface: I'll assume you're using WI for Web or PNAgent.  You'll need at least 2 WIs.  These servers will need to sit behind a set of load balancers (Netscaler, F5, Cisco)  in Active/Passive mode or Active/Active mode (not sure about Active/Active since I'm not a networking guy).
a. This way if a load balancer fails or if a WI fails it will fail over to the secondary.
2. XML Brokers:  The WIs use these servers to authenticate users, enumerate what applications the user has access to, and direct them to the appropriate server (ex. typically the server with the least load that hosts the application).
a. These servers can be dedicated, your ZDC(s) (If you have dedicated ZDCs and a Most Preferred and Preferred), or servers hosting applications or desktops.
b. As to what option in "a", I  would say with the size of your environment you don't need dedicated XML brokers and can use the ZDC(s).  You'll want to use two obviously for redundancy.
c. You can even load balance the XML brokers with a load balancer, but I would consider this extreme even for a large environment (100's of servers/1000's of users).
3. ZDC servers:  Discussed in "#2", but with an environment your size I would say you specify an Most Preferred and Preferred ZDC.  Now these can be dedicated or they can be servers hosting applications or desktops.  You could probably get away with using servers hosting applications or desktops that have low utilization, but this is hard to say without knowing your environment in detail (server specs, users per server, etc.)
4. Datastore: I would say for an environment your size you do not need to use any SQL redundancy.  If a Datastore goes down, the farm will work indefinitely but while it is down you can't make any changes to the farm.  You could implement SQL HA, but it may be overkill.
5. License Server:  Just one.  Even if your license server goes down you have 30 days to get it back up.
Now you say that you have 4 farms. You'll need to consider "#2" and "#3" for each farm.  As for "4" you could have all the datastores on the same SQL server, but again if you lose that server you can't make any modifications to any farm till it is back online.
Another topic of discussion, but if business requirements allow you could consolidate the servers into one farm.
Carl WebsterCommented:
Do you already have 4 farms?

A lot of the customers I talk to want HA but really don't understand what all that means.  For example, they want multiple Web Interface servers, multiple XenApp servers, a SQL Server cluster, etc.  But then they have 1 switch, 1 firewall, 1 router, 1 Internet connection, 1 telco provider, 1 data center, 1 electrical feed, 1 HVAC unit, etc.

You can have all the HA you want and can afford for your server environment and your HVAC system goes out on a Friday night and your data center shuts down.  Now what did all the server HA buy you?

Citrix provides all the software and hardware you need for your XenApp HA needs (if you can afford the stuff).

Having multiple XenApp servers allows the servers to spread the load and if 1 server goes down the others will handle the load.  BUT the sessions active on the down server or just lost.

You can have multiple Web Interface servers in a Windows NLB configuration but that isn't true HA.  One, or more, Web Interface servers could be running but not functioning and NLB will still send connections to the non-functioning servers because they are still "up and running".  That is where Netscaler and Branch Repeater come in handy.

To answer the rest of what you need, I will echo KrAzY and ask for more info.  How many users do you want to handle?  How many apps will you be serving?  Will those apps be hosted apps, streamed apps, XP VM mode apps, published desktops, content?  If streamed, will they be streamed to the server, the client, or both?  If to the client, will the streamed apps be available offline?

What SQL Server will you be using for your data store?  MS SQL (2000, 2005, 2008), Oracle, DB2?

Will you be using per-user or per-device terminal server (now Remote Desktop Services) mode?

Will you be using or planning to go to VDI in the future?

Will you be using 32-bit or 64-bit server OS?

That is enough for now.

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Carl WebsterCommented:
Oh yeah, one more very important question:  will you be using physical servers, virtual servers or a combination of both?
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