1. Deploying Global Server Load Balancing
Using Persistent Methods
Sam Cohoon
May 21, 2013

2. Global Server Load Balancing
In this session you will learn about:
General deployment scenarios and simple configuration of GSLB
Discuss popular load balancing methods
Methods of ensuring users have persistent connections
How to troubleshoot problems
We will describe a basic setup and how to ensure users connect to the optimal site, including troubleshooting.

3. Global Server Load Balancing
Old Technology
Multiple sites are now cheap enough that the technology is more widely implemented

4. Global Server Load Balancing
Common to see sites in US, Europe and Asia

5. What is GSLB?
Global Server Load Balancing (GSLB) describes a range of technologies to distribute resources around the Internet
for various purposes.
Critical Applications, multiple Geos
Intelligently balance traffic
Disaster Recovery
Load sharing
Performance, including proximity

6. DNS
The Citrix NetScaler implementation of Global Server Load Balancing GSLB is Domain Name System (DNS) based.
Citrix Netscaler implementation of GSLB is DNS-based

7. DNS
Citrix Netscaler implementation of GSLB is DNS-based

8. GSLB Typical Setup -Typical setup with two geographical locations.
Active-active data center setup.
Active-standby data center setup.
Proximity setup.
-The Netscalers are DNS servers share information using Metric Exchange Protocol
Metric Exchange Protocol (MEP)
MEP is a proprietary protocol used by the NetScaler to exchange site information to other sites participating in GSLB
The communication process is on TCP port 3011 (or 3009 for secure communication) and must be open on firewalls
Site to site monitoring
Distributes site metrics, network metrics, persistence information

9. Global Server Load Balancing Components
GSLB Components

10. Components Diagram of GSLB – Flow
Requests come in from client about domain
Site (DNS server) checks with
GSLB Vserver, which looks at
GSLB Services > linked to Vservers>Services
GSLB domain: Publicly resolvable domain (zone) that the GSLB deployment responds to
GSLB site: Top level entity for linking remote sites, sharing monitoring data.
GSLB vserver
GSLB service

11. How it works - Summary DNS and MEP
Components: GSLB domain, GSLB site, GSLB vserver, GSLB service
Summary:
*GSLB enables distribution of traffic across multiple sites, manages disaster recovery, and ensures that applications are consistently accessible.
*MEP & DNS
*Components
***GSLB domain, GSLB site, GSLB vserver, GSLB service

12. Global Server Load Balancing Configuration
Configuring GSLB

13. GSLB Configuration
Where do I start?
Where do I start? Wizard

14. GSLB Wizard Configuring GSLB vServer
A GSLB virtual server is an entity that represents one or more GSLB services and balances traffic between them.
It evaluates the configured GSLB methods or algorithms to select a GSLB service to which to send the client request.
To make a NetScaler appliance the authoritative DNS server for a domain, you must bind the domain to the GSLB virtual server.
When you bind a domain to a GSLB virtual server, the NetScaler adds an address record for the domain, containing the name of the GSLB virtual server.

15. GSLB DNS DOMAIN Note: this is a dynamic record , we do not see IP.
GSLB responds to DNS with the IP addresses of the services, as determined by the configured GSLB method.

16. GSLB Methods
GSLB methods are algorithms that the GSLB virtual server uses to select the best-performing GSLB service.

17. GSLB Methods
GSLB methods are algorithms that the GSLB virtual server uses to select the best-performing GSLB service.
Default Method – Least Connection
GSLB methods:
Round Robin, Least Connection, Least Response Time, Least Bandwidth, Least Packets, Source IP Hash, Custom Load, Round Trip Time (RTT)
&
Static Proximity

18. GSLB Methods
GSLB Methods – Source IP Persistence

19. GSLB Sites -A GSLB site is a representation of a data center.
-logical grouping of GSLB virtual servers, services, and other network entities.
-All sites must be configured the same.
-at each site, you configure the local GSLB site and each remote GSLB site.

20. GSLB Sites -All sites must be configured the same.
-at each site, you configure the local GSLB site and all remote sites.

21. GSLB Sites
When we click the next button we get reminded to add service on this site

22. GSLB Service A GSLB service represents LB or CS Vservers.
This is where we configure Site Persistence.

23. Configuration Summary
Configuration Summary Page

24. Configuring Authoritative DNS - ADNS
An ADNS service can be used for global server load balancing.
When you create an ADNS service, the NetScaler responds to DNS queries on the configured ADNS service IP and port.
Note: For the NetScaler to be authoritative, you must also create SOA and NS records.
Note: You can configure the ADNS service to use MIP, SNIP, or any new IP address.
**Also possible to use a DNS VIP.

25. GSLB Visualizer
Viewing and Configuring a GSLB Setup by Using the GSLB Visualizer
-The visualizer displays all configured GSLB domains, GSLB services, GSLB sites, ADNS services, and any monitors that are bound to the services.
-It also displays all the load balancing, content switching, cache redirection, and Access Gateway virtual servers that the GSLB services represent.
Note: If you want to view the configurations of remote GSLB sites, you must configure the sites with public IP addresses and enable management access for each of them.

26. Synchronizing Configuration
Each Netscaler needs one Local GSLB site and all the other Remote sites.
All sites need the same configuration.
There is a GSLB configuration synchronization option.
SYNCHRONIZATION
-Each Netscaler needs one Local GSLB site and all the other Remote sites.
-All sites need the same configuration.
-To have the same configuration on all the GSLB sites, you can use the NetScaler’ configuration synchronization option.

27. Customizing your GSLB Configuration

28. GSLB Load Balancing methods
The NetScaler GSLB methods: Round Trip Time (RTT) Static Proximity
GSLB METHOD
RTT
Static Proximity

29. Local DNS IP (LDNS)
IP address that is being tested against is not an actual client IP address it is the nameserver that is resolving the IP address on behalf of the client. We refer to this as the “LDNS” IP address for the client’s local DNS IP address.
-LDNS
-IP address that is being tested against is not an actual client IP address
- it is the nameserver that is resolving the IP address on behalf of the client.
-We refer to this as the “LDNS” for the client’s local DNS IP address.

30. IP-address based static proximity database is a UNIX-based ASCII file.
GSLB Static Proximity
IP-address based static proximity database is a UNIX-based ASCII file.
-The static proximity method for GSLB uses an IP-address based database to determine the proximity between the client’s local DNS server and the GSLB sites.
-The NetScaler appliance responds with the IP address of a site that best matches the proximity criteria.
-set locationParameter
-Use DNS Policies to override the static proximity method with preferred locations
-Third party vendor, various formats

31. GSLB Static Proximity Troubleshooting
nsmap -t –d
nsmap -t -d
Enter IP address to to test (dot notation) or q to exit:
To perform a static proximity-based decision, the NetScaler appliance compares the location attributes (qualifiers) derived from the IP address of the local DNS server resolver with the location attributes of the participating sites.
Set locationParameter
Nsmap –t –d
Nmap can also be used to convert database file formats

32. GSLB Static Proximity Troubleshooting
> show locationparameter
Static Proximity
Database mode: Not applicable
Flushing: Idle; Loading: Idle
Context: geographic
Qualifier 1 label: Continent
Qualifier 2 label: Country
Qualifier 3 label: Region
Qualifier 4 label: City
Qualifier 5 label: ISP
Qualifier 6 label: Organization
Location file (format: Not applicable):
Not loaded
Lines: 0 Warnings: 0 Errors: 0
Current static entries: 0 Current custom entries: 0
Done
Show Location Parameter
-Only one location file can be loaded on a NetScaler appliance. Adding a new location file overrides the existing file.
-In an HA pair, the file must be loaded in the same location on both netscalers

33. GSLB Dynamic RTT
Dynamic RTT : measure from each “site” NetScaler to the remote LDNS
Three Monitors:
Ping of IP address (LDNS-PING)
DNS TCP probe
DNS UDP query
Dynamic RTT load balancing makes use of direct measurements from each “site” NetScaler to the remote LDNS IP address to find the site closest to the user’s LDNS.
As a result of this, RTT can reduce maintenance on the
configurations versus the static table method of proximity, and in theory provide more accurate locations for users.
To measure the performance, three monitors are activated on the remote IP address in the following order:
First, Ping of IP address (LDNS-PING), if that fails; then
A DNS TCP probe (the syn-ack response time is used
A DNS UDP query for the domain “.” (LDNS-DNS).
>Show ldns

34. Global Server Load Balancing Persistence
Customizing your GSLB Configuration

35. Persistence Based on Source IP
The GSLB virtual server is responsible for DNS-based site persistence, and it controls the site persistence Persistence Table All sites must use the same set of persistence identifiers on the GSLB virtual servers.
-Source-IP Persistence
-persistence table check first
-same set of persistence identifiers must be configured on the GSLB virtual servers in all data centers.
-A persistence identifier is a number used by the data centers to identify a particular GSLB virtual server.

36. GSLB Persistence – Source IP Troubleshooting
SourceIP Persistence Setup on the GSLB VServer

37. GSLB Persistence – Source IP Troubleshooting
Show Persistent Sessions
This persistence information is share between sites.

38. Global Server Load Balancing HTTP Cookie Persistence
Customizing your GSLB Configuration - HTTP Cookie Persistence

39. Persistence Based on HTTP Cookies
HTTP-request level
Connection proxy
HTTP redirect.
-Persistence at the HTTP-request level by using connection proxy and HTTP redirect. --The NetScaler inserts the site cookie in the first HTTP response.
-Site cookie contains info about GSLB Service that has the persistent connection.

40. HTTP Connection Proxy If the client gets sent to the wrong site:
The other site creates a connection to the GSLB site that inserted the site cookie, and proxies the client request
- If wrong site, that site creates a connection to the GSLB site that inserted the site cookie, proxies the client request to the original site, receives a response from the original GSLB site, relays that response back to the client, and closes the connection.

41. HTTP Connection Proxy
Troubleshooting: this slide shows a network trace of connection proxy in action

42. HTTP Redirect Persistence
Redirect persistence can be used only: For HTTP or HTTPS protocols. If the domain name in the request is a GSLB Domain When a backup VIP or a GSLB local service is DOWN
Redirect persistence can be used only:
For HTTP or HTTPS protocols.
If the domain name is present in the request (either in the URL or in the HOST header), and the domain is a GSLB domain.
When the request is received on a backup VIP or a GSLB local service that is in the DOWN state.

43. GSLB Persistence – HTTPRedirect
HTTP Redirect GUI Slide
Site Prefix SiteA is prepended

44. GSLB Persistence – HTTP Redirect
siteawww.example.com

45. Global Server Load Balancing Troubleshooting
GSLB Troubleshooting

46. GSLB Troubleshooting
> sh gslb site
1) _siteB ( ) Site Type: LOCAL
Metric exchange: ENABLED Public IP:
Network metric exchange: ENABLED Persistence session exchange: ENABLED
Trigger Monitors: ALWAYS
2) _siteA ( ) Site Type: REMOTE
Metric exchange: ENABLED Site Metric MEP Status: DOWN Public IP:
sh GSLB site
-MEP
-Network metric exchange
-Persistence session exchange

47. GSLB Troubleshooting sh GSLB Vserver -State -Lb Method
> sh gslb vserver 1) - HTTP State: UP DNS Record Type: A Last state change was at Thu Apr 11 22:17: Time since last state change: 11 days, 23:01: Configured Method: LEASTCONNECTION Current Method: Round Robin Reason: Bound service's state changed to UP BackupMethod: ROUNDROBIN No. of Bound Services : 2 (Total) 1 (Active) Persistence: SOURCEIP Persistence Mask: Persistence v6MaskLength: 128 Persistence Timeout: 2 min Persistence ID: 2 Disable Primary Vserver on Down: DISABLED Site Persistence: ConnectionProxy
sh GSLB Vserver
-State
-Lb Method
-Current Method :
-Backup method RR
-No of services
Persistence:
Persistence mask and timeout.
Site persistence: Connection Proxy

48. GSLB Troubleshooting sh GSLB Service -Local and Remote
1) _80_gslbsvc ( : 80)- HTTP Server: State: UP
Effective State: UP
Max Conn: Max Bandwidth: 0 kbits
PublicIP: PublicPort: 80
Type: LOCAL Site Name: _siteB
Site Prefix: SiteB Site Persistence: ConnectionProxy
Threshold: BELOW Monitor Threshold : 0
2) _80_gslbsvc ( : 80)- HTTP Server: State: DOWN
Effective State: DOWN
PublicIP: PublicPort: 80
Type: REMOTE Site Name: _siteA
Site Prefix: SiteA Client IP: DISABLED
Down state flush: DISABLED
Site Persistence: ConnectionProxy
sh GSLB Service
-Local and Remote

49. GSLB Troubleshooting
nsconmsg -K newnslog -d stats | grep gslb nsconmsg -g glsb -d current -s disptime=1
Nsconmsg –d stats | grep glsb -g

50. Resources
SYNCHRONIZATION
-Each Netscaler needs one Local GSLB site and all the other Remote sites.
-All sites need the same configuration.
-To have the same configuration on all the GSLB sites, you can use the NetScaler’ configuration synchronization option.

51. Global Server Load Balancing
Jump In

52. Before you leave…
Conference surveys are available online at starting Friday, May 24 at 9:00 a.m. PT
Provide your feedback by 4:00 p.m. PT that day and you’ll receive a $30 Amazon.com gift card via
Download presentations starting Monday, June 3, from your My Conference Planning tool located within the My Account section