1. High Availability for XenApp
Nikolay Shadrin
Systems Engineer

2. Agenda
Identification number 1
Agenda item
Education
Implementation
Conclusion
© 2007 Citrix Systems, Inc. — All rights reserved 2

3. Where It Fits

4. Determine If There Is A Need
• Break it down into small components
• Server Load Balancing
• Global Server Load Balancing
© 2007 Citrix Systems, Inc. — All rights reserved 4

5. Server Load Balancing - Qualification
• Does the architecture have multiple
• Access Gateway devices
• Web Interface servers
• XML Brokers
• No: Single Point of Failure
• Yes: How are they load balanced
© 2007 Citrix Systems, Inc. — All rights reserved 5

6. Server Load Balancing - Qualification
D
• How are they load balanced N
• DNS Round Robin S
• Hardware or Software Load Balancer
• DNS: Not an intelligent solution
• Hardware or Software:
How does it determine availability
© 2007 Citrix Systems, Inc. — All rights reserved 6

7. Server Load Balancing - Qualification
• Hardware or Software: How does it determine availability
• Server availability: A service could still be offline and the load balancer would
not detect
• Service availability: Identify if the service is online, but could still be non-
functioning
• Service response: Intelligent solution as verifies services are running and
responding correctly
• NetScaler provides service response analysis with
• Web Interface monitor
• XML Broker monitor
© 2007 Citrix Systems, Inc. — All rights reserved 7

8. Global Server Load Balancing - Qualification
• Is the environment spread across
multiple sites?
• No: No need for GSLB but there is a
site failure risk
• Yes
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9. Global Server Load Balancing - Qualification
• How are the sites load balanced?
• Multiple Addresses: Not intelligent and requires users to remember different
access scenarios
• DNS Round Robin: Not intelligent
• Hardware Load Balancer Solution
© 2007 Citrix Systems, Inc. — All rights reserved 9

10. Global Server Load Balancing - Qualification
• How is the harware load balancer monitoring site
availability?
• Server Response: Server could respond, but services not available
• Service Availability: Service could be running but not functioning
• Service Response: Verifies services are responding correctly.
• NetScaler uses service response for XenApp
• NetScaler combines multiple services to determine site
availability
© 2007 Citrix Systems, Inc. — All rights reserved 10

11. © 2007 Citrix Systems, Inc. — All rights reserved 11

12. Terminology

13. Basic Citrix NetScaler LB Concept
Monitor
Service Server
vserver
Service Server
Monitor
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14. What is a vserver?
• Object on NetScaler that Monitor
receives client
connections/requests Service Server
• Distributes client vserver
requests
among bound services
• Can be used for external and internal-only resources Service Server
Monitor
© 2007 Citrix Systems, Inc. — All rights reserved 14

15. What is a Service?
• Network endpoint Monitor
• Server IP
• Server Port Service Server
• Protocol
vserver
• Services bound to a vserver
Service Server
• Service can represent
• A server running Web Interface
• A server running as a XML Broker Monitor
© 2007 Citrix Systems, Inc. — All rights reserved 15

16. What is a Monitor?
• Periodic probe of a server Monitor
or service
Service
• Monitors are bound
Server
to services vserver
• Verifies health of the
Service Server
bound service
• Provides feedback to Monitor
NetScaler kernel
© 2007 Citrix Systems, Inc. — All rights reserved 16

17. Load Balancing Method
• Used to determine appropriate backend system to forward requests
Monitor
to
• Least Connections (default) Service Server
• Round Robin
• Least Response Time vserver
• Least Bandwidth
• Least Packets Service Server
• Token
• Hashing (of URL, Domain name, Source/Destination IP Address)
Monitor
• Round Trip Time (RTT)
• Source/Destination IP Hash
© 2007 Citrix Systems, Inc. — All rights reserved 17

18. Persistence methods
Monitor
• Used to keep clients going to the same server/service
Service Server
• Typical persistance methods:
• Source-IP vserver
• Cookie Insert
Service Server
• SSL Session ID
• URL Passive
• Custom Server ID Monitor
• Rule
© 2007 Citrix Systems, Inc. — All rights reserved 18

19. High Availability
• Deployed in HA for maximum uptime
• Diagrams
• Only show 1 NetScaler for readability
• Assumption is deployment of HA pairs
• Remember
=
© 2007 Citrix Systems, Inc. — All rights reserved 19

20. Terminology Summary
Terminology Definition
vserver Virtual IP address on the NetScaler switch for the load balanced pool
Server Interface IP of a physical server included in a load balanced group
Service The port and protocol being load balanced on a server
Monitor The method used to assess server availability and response time
Load balancing method The method by which traffic is distributed among
the services
Persistence The method used for maintaining client-server affinity
© 2007 Citrix Systems, Inc. — All rights reserved 20

21. Proof of Concept
Walk Through

22. Initial Architecture
User Access Gateway XML Broker
Web Interface
172.16.0.22 172.16.0.53
172.16.0.51
Web Interface XML Broker
Site MSP 172.16.0.52 172.16.0.54
Site FLL
User Access Gateway
Web Interface XML Broker
172.16.0.27
172.16.0.56 172.16.0.57
© 2007 Citrix Systems, Inc. — All rights reserved 22

23. Initial Architecture Challenges
• Possibility of users being denied their applications
• Web Interface: Not load balanced, manual change if primary fails
• Access Gateway Web Interface Site: Can only configure a single Web Interface
• XML Black Hole: Service is available but not functioning
• Site B Failure: Multiple single points of failure
• Configuration challenges
• Similar devices have different configurations
© 2007 Citrix Systems, Inc. — All rights reserved 23

24. Initial Architecture Solution
• Upgrade to NetScaler-Enterprise or Platinum from
• Secure Gateway
• Access Gateway (All Editions)
• NetScaler-Enterprise or Platinum gets you
• Server Load Balancing
• Global Server Load Balancing
• Access Gateway Enterprise SSL-VPN
• Three phased approach:
• Phase I: Server Load Balancing
• Phase II: Farm Reconfiguration
• Phase III: Global Server Load Balancing
© 2007 Citrix Systems, Inc. — All rights reserved 24

25. Phase I:
Server Load Balancing

26. Web Interface and XML Broker Load Balancing
Before
Web Interface XML Broker
172.16.0.51 172.16.0.53
Access Gateway
172.16.0.22
Web Interface XML Broker
172.16.0.52 172.16.0.54
© 2007 Citrix Systems, Inc. — All rights reserved 26

27. Web Interface and XML Broker Load Balancing
After
Web Interface XML Broker
WI VIP: XML VIP: 172.16.0.53
172.16.0.51
Access Gateway 172.16.0.22 172.16.0.23
172.16.0.22
Web Interface XML Broker
172.16.0.52 172.16.0.54
© 2007 Citrix Systems, Inc. — All rights reserved 27

28. Web Interface and XML Broker Load Balancing
Steps
• Prepare the NetScalers
• Server Load Balancing Configuration
© 2007 Citrix Systems, Inc. — All rights reserved 28

29. Server Load Balancing Summary
SLB Service Monitor
172.16.0.53 CTXXML
HTTP 80 Notepad
XML Broker
SLB vserver 172.16.0.53
172.16.0.24
SLB Service Monitor
172.16.0.54 CTXXML
HTTP 80 Notepad
XML Broker
172.16.0.54
NetScaler SLB Service Monitor
172.16.0.21 172.16.0.51 CTXWEB
HTTP 80 Site Path
Web Interface
SLB vserver
172.16.0.51
172.16.0.23
SLB Service Monitor
172.16.0.52 CTXWEB
HTTP 80 Site Path
Web Interface
172.16.0.52
© 2007 Citrix Systems, Inc. — All rights reserved 29

30. Phase II:
Farm Reconfiguration

31. Farm Reconfiguration
Before
Web Interface XML Broker
WI VIP: XML VIP: 172.16.0.53
172.16.0.51
Access Gateway 172.16.0.22 172.16.0.23
172.16.0.22
Web Interface XML Broker
172.16.0.52 172.16.0.54
© 2007 Citrix Systems, Inc. — All rights reserved 31

32. Farm Reconfiguration
After
Web Interface XML Broker
WI VIP: XML VIP: 172.16.0.53
172.16.0.51
172.16.0.22 172.16.0.23
Access Gateway
172.16.0.22
Web Interface XML Broker
172.16.0.52 172.16.0.54
© 2007 Citrix Systems, Inc. — All rights reserved 32

33. Farm Reconfiguration
Steps
• Reconfigure Web Interface
• Reconfigure Access Gateway
• Test
© 2007 Citrix Systems, Inc. — All rights reserved 33

34. STA Load Balancing
• Do not change the Access Gateway STA settings
• Correct STA selected based on STA identifier
• Load balancing breaks this functionality
© 2007 Citrix Systems, Inc. — All rights reserved 34

35. Farm Reconfiguration - Summary
Device Parameter Old Setting New Setting
AG WI Home 172.16.0.51 172.16.0.23
Page
WI1 STA http://172.16.0.53/path http://172.16.0.24/path
& http://172.16.0.54/path
WI2 XML Broker 172.16.0.53 172.16.0.24
172.16.0.54
© 2007 Citrix Systems, Inc. — All rights reserved 35

36. Phase III:
Global Server Load Balancing

37. Intelligent GSLB
• Only send users to sites with complete availability
• If Access Gateway responds, the site could still
be down
• Web Interface disruptions
• XML Broker disruptions
• STA disruptions
• Define and configure GSLB based on layers
© 2007 Citrix Systems, Inc. — All rights reserved 37

38. Global Server Load Balancing Preview
SLB Service Monitor
172.16.0.53 CTXXML
GSLB
HTTP 80 Notepad
Monitor XML Broker
Access Gateway
SLB vserver SSL 172.16.0.53
172.16.0.22
172.16.0.24
SLB Service Monitor
GSLB vserver GSLB Service GSLB 172.16.0.54 CTXXML
SSL 443 172.16.0.22 Monitor HTTP 80 Notepad
agee.company.com SSL 443 HTTP XML Broker
172.16.0.54
SLB Service Monitor
GSLB
172.16.0.51 CTXWEB
Monitor
HTTP 80 Site Path
HTTP Web Interface
SLB vserver
172.16.0.51
172.16.0.23
SLB Service Monitor
172.16.0.52 CTXWEB
HTTP 80 Site Path
Web Interface
172.16.0.52
© 2007 Citrix Systems, Inc. — All rights reserved 38

39. Global Server Load Balancing Configuration
Steps
• Build GSLB Sites
• Build GSLB Monitors
• Build GSLB Services
• Build GSLB Virtual Server
• Update DNS
• Test
© 2007 Citrix Systems, Inc. — All rights reserved 39

40. Global Server Load Balancing Summary
SLB Service Monitor
172.16.0.53 CTXXML
GSLB
HTTP 80 Notepad
Monitor XML Broker
Access Gateway
SLB vserver SSL 172.16.0.53
172.16.0.22
172.16.0.24
SLB Service Monitor
GSLB vserver GSLB Service GSLB 172.16.0.54 CTXXML
SSL 443 172.16.0.22 Monitor HTTP 80 Notepad
agee.company.com SSL 443 HTTP XML Broker
172.16.0.54
SLB Service Monitor
GSLB
172.16.0.51 CTXWEB
Monitor
HTTP 80 Site Path
HTTP Web Interface
SLB vserver
172.16.0.51
172.16.0.23
SLB Service Monitor
172.16.0.52 CTXWEB
HTTP 80 Site Path
Web Interface
172.16.0.52
© 2007 Citrix Systems, Inc. — All rights reserved 40

41. Final Architecture
Web Interface XML Broker
WI VIP: 172.16.0.51 XML VIP: 172.16.0.53
172.16.0.22 172.16.0.23
NetScaler
172.16.0.21
DNS Web Interface XML Broker
Site MSP 172.16.0.52 172.16.0.54
Site FLL
User
WI VIP: XML VIP:
172.16.0.22 172.16.0.23
NetScaler
Web Interface XML Broker
172.16.0.26
172.16.0.56 172.16.0.57
© 2007 Citrix Systems, Inc. — All rights reserved 41

42. © 2007 Citrix Systems, Inc. — All rights reserved 42

43. Summary

44. Global Availability
• XenApp used to deliver critical line-of-business applications
• Integrate global server load balancing and server load balancing for
maximum availabilty
• NetScaler integration with XenApp makes it extremely easy
• XenApp load balancing wizard
• Specialized monitors for Web Interface and XML Broker
© 2007 Citrix Systems, Inc. — All rights reserved 44

45. Available Tools
• GSLB for XenApp:
http://support.citrix.com/
• Reference Architecture
• Design Considerations
• Implementation Guide
• TechTalk Webcasts:
http://www.citrix.com/English/NE/events/byType.asp?etype=1441
© 2007 Citrix Systems, Inc. — All rights reserved 45

46. © 2007 Citrix Systems, Inc. — All rights reserved 46