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Global Server Load Balancing Support
------------------------------------

CloudStack supports Global Server Load Balancing (GSLB) functionalities
to provide business continuity, and enable seamless resource movement
within a CloudStack environment. CloudStack achieve this by extending
its functionality of integrating with NetScaler Application Delivery
Controller (ADC), which also provides various GSLB capabilities, such as
disaster recovery and load balancing. The DNS redirection technique is
used to achieve GSLB in CloudStack.

In order to support this functionality, region level services and
service provider are introduced. A new service 'GSLB' is introduced as a
region level service. The GSLB service provider is introduced that will
provider the GSLB service. Currently, NetScaler is the supported GSLB
provider in CloudStack. GSLB functionality works in an Active-Active
data center environment.


About Global Server Load Balancing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Global Server Load Balancing (GSLB) is an extension of load balancing
functionality, which is highly efficient in avoiding downtime. Based on
the nature of deployment, GSLB represents a set of technologies that is
used for various purposes, such as load sharing, disaster recovery,
performance, and legal obligations. With GSLB, workloads can be
distributed across multiple data centers situated at geographically
separated locations. GSLB can also provide an alternate location for
accessing a resource in the event of a failure, or to provide a means of
shifting traffic easily to simplify maintenance, or both.


Components of GSLB
^^^^^^^^^^^^^^^^^^

A typical GSLB environment is comprised of the following components:

-  **GSLB Site**: In CloudStack terminology, GSLB sites are represented
   by zones that are mapped to data centers, each of which has various
   network appliances. Each GSLB site is managed by a NetScaler
   appliance that is local to that site. Each of these appliances treats
   its own site as the local site and all other sites, managed by other
   appliances, as remote sites. It is the central entity in a GSLB
   deployment, and is represented by a name and an IP address.

-  **GSLB Services**: A GSLB service is typically represented by a load
   balancing or content switching virtual server. In a GSLB environment,
   you can have a local as well as remote GSLB services. A local GSLB
   service represents a local load balancing or content switching
   virtual server. A remote GSLB service is the one configured at one of
   the other sites in the GSLB setup. At each site in the GSLB setup,
   you can create one local GSLB service and any number of remote GSLB
   services.

-  **GSLB Virtual Servers**: A GSLB virtual server refers to one or more
   GSLB services and balances traffic between traffic across the VMs in
   multiple zones by using the CloudStack functionality. It evaluates
   the configured GSLB methods or algorithms to select a GSLB service to
   which to send the client requests. One or more virtual servers from
   different zones are bound to the GSLB virtual server. GSLB virtual
   server does not have a public IP associated with it, instead it will
   have a FQDN DNS name.

-  **Load Balancing or Content Switching Virtual Servers**: According to
   Citrix NetScaler terminology, a load balancing or content switching
   virtual server represents one or many servers on the local network.
   Clients send their requests to the load balancing or content
   switching virtual server's virtual IP (VIP) address, and the virtual
   server balances the load across the local servers. After a GSLB
   virtual server selects a GSLB service representing either a local or
   a remote load balancing or content switching virtual server, the
   client sends the request to that virtual server's VIP address.

-  **DNS VIPs**: DNS virtual IP represents a load balancing DNS virtual
   server on the GSLB service provider. The DNS requests for domains for
   which the GSLB service provider is authoritative can be sent to a DNS
   VIP.

-  **Authoritative DNS**: ADNS (Authoritative Domain Name Server) is a
   service that provides actual answer to DNS queries, such as web site
   IP address. In a GSLB environment, an ADNS service responds only to
   DNS requests for domains for which the GSLB service provider is
   authoritative. When an ADNS service is configured, the service
   provider owns that IP address and advertises it. When you create an
   ADNS service, the NetScaler responds to DNS queries on the configured
   ADNS service IP and port.


How Does GSLB Works in CloudStack?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Global server load balancing is used to manage the traffic flow to a web
site hosted on two separate zones that ideally are in different
geographic locations. The following is an illustration of how GLSB
functionality is provided in CloudStack: An organization, xyztelco, has
set up a public cloud that spans two zones, Zone-1 and Zone-2, across
geographically separated data centers that are managed by CloudStack.
Tenant-A of the cloud launches a highly available solution by using
xyztelco cloud. For that purpose, they launch two instances each in both
the zones: VM1 and VM2 in Zone-1 and VM5 and VM6 in Zone-2. Tenant-A
acquires a public IP, IP-1 in Zone-1, and configures a load balancer
rule to load balance the traffic between VM1 and VM2 instances.
CloudStack orchestrates setting up a virtual server on the LB service
provider in Zone-1. Virtual server 1 that is set up on the LB service
provider in Zone-1 represents a publicly accessible virtual server that
client reaches at IP-1. The client traffic to virtual server 1 at IP-1
will be load balanced across VM1 and VM2 instances.

Tenant-A acquires another public IP, IP-2 in Zone-2 and sets up a load
balancer rule to load balance the traffic between VM5 and VM6 instances.
Similarly in Zone-2, CloudStack orchestrates setting up a virtual server
on the LB service provider. Virtual server 2 that is setup on the LB
service provider in Zone-2 represents a publicly accessible virtual
server that client reaches at IP-2. The client traffic that reaches
virtual server 2 at IP-2 is load balanced across VM5 and VM6 instances.
At this point Tenant-A has the service enabled in both the zones, but
has no means to set up a disaster recovery plan if one of the zone
fails. Additionally, there is no way for Tenant-A to load balance the
traffic intelligently to one of the zones based on load, proximity and
so on. The cloud administrator of xyztelco provisions a GSLB service
provider to both the zones. A GSLB provider is typically an ADC that has
the ability to act as an ADNS (Authoritative Domain Name Server) and has
the mechanism to monitor health of virtual servers both at local and
remote sites. The cloud admin enables GSLB as a service to the tenants
that use zones 1 and 2.

|gslb.png|

Tenant-A wishes to leverage the GSLB service provided by the xyztelco
cloud. Tenant-A configures a GSLB rule to load balance traffic across
virtual server 1 at Zone-1 and virtual server 2 at Zone-2. The domain
name is provided as A.xyztelco.com. CloudStack orchestrates setting up
GSLB virtual server 1 on the GSLB service provider at Zone-1. CloudStack
binds virtual server 1 of Zone-1 and virtual server 2 of Zone-2 to GLSB
virtual server 1. GSLB virtual server 1 is configured to start
monitoring the health of virtual server 1 and 2 in Zone-1. CloudStack
will also orchestrate setting up GSLB virtual server 2 on GSLB service
provider at Zone-2. CloudStack will bind virtual server 1 of Zone-1 and
virtual server 2 of Zone-2 to GLSB virtual server 2. GSLB virtual server
2 is configured to start monitoring the health of virtual server 1 and
2. CloudStack will bind the domain A.xyztelco.com to both the GSLB
virtual server 1 and 2. At this point, Tenant-A service will be globally
reachable at A.xyztelco.com. The private DNS server for the domain
xyztelcom.com is configured by the admin out-of-band to resolve the
domain A.xyztelco.com to the GSLB providers at both the zones, which are
configured as ADNS for the domain A.xyztelco.com. A client when sends a
DNS request to resolve A.xyztelcom.com, will eventually get DNS
delegation to the address of GSLB providers at zone 1 and 2. A client
DNS request will be received by the GSLB provider. The GSLB provider,
depending on the domain for which it needs to resolve, will pick up the
GSLB virtual server associated with the domain. Depending on the health
of the virtual servers being load balanced, DNS request for the domain
will be resolved to the public IP associated with the selected virtual
server.


Configuring GSLB
~~~~~~~~~~~~~~~~

To configure a GSLB deployment, you must first configure a standard load
balancing setup for each zone. This enables you to balance load across
the different servers in each zone in the region. Then on the NetScaler
side, configure both NetScaler appliances that you plan to add to each
zone as authoritative DNS (ADNS) servers. Next, create a GSLB site for
each zone, configure GSLB virtual servers for each site, create GLSB
services, and bind the GSLB services to the GSLB virtual servers.
Finally, bind the domain to the GSLB virtual servers. The GSLB
configurations on the two appliances at the two different zones are
identical, although each sites load-balancing configuration is specific
to that site.

Perform the following as a cloud administrator. As per the example given
above, the administrator of xyztelco is the one who sets up GSLB:

#. In the cloud.dns.name global parameter, specify the DNS name of your
   tenant's cloud that make use of the GSLB service.

#. On the NetScaler side, configure GSLB as given in `Configuring Global
   Server Load Balancing (GSLB) 
   <http://support.citrix.com/proddocs/topic/netscaler-traffic-management-10-map/ns-gslb-config-con.html>`_:

   #. Configuring a standard load balancing setup.

   #. Configure Authoritative DNS, as explained in `Configuring an
      Authoritative DNS Service 
      <http://support.citrix.com/proddocs/topic/netscaler-traffic-management-10-map/ns-gslb-config-adns-svc-tsk.html>`_.

   #. Configure a GSLB site with site name formed from the domain name
      details.

      Configure a GSLB site with the site name formed from the domain
      name.

      As per the example given above, the site names are A.xyztelco.com
      and B.xyztelco.com.

      For more information, see `Configuring a Basic GSLB Site 
      <http://support.citrix.com/proddocs/topic/netscaler-traffic-management-10-map/ns-gslb-config-basic-site-tsk.html>`_.

   #. Configure a GSLB virtual server.

      For more information, see `Configuring a GSLB Virtual Server 
      <http://support.citrix.com/proddocs/topic/netscaler-traffic-management-10-map/ns-gslb-config-vsvr-tsk.html>`_.

   #. Configure a GSLB service for each virtual server.

      For more information, see `Configuring a GSLB Service 
      <http://support.citrix.com/proddocs/topic/netscaler-traffic-management-10-map/ns-gslb-config-svc-tsk.html>`_.

   #. Bind the GSLB services to the GSLB virtual server.

      For more information, see `Binding GSLB Services to a GSLB Virtual
      Server <http://support.citrix.com/proddocs/topic/netscaler-traffic-management-10-map/ns-gslb-bind-svc-vsvr-tsk.html>`_.

   #. Bind domain name to GSLB virtual server. Domain name is obtained
      from the domain details.

      For more information, see `Binding a Domain to a GSLB Virtual
      Server <http://support.citrix.com/proddocs/topic/netscaler-traffic-management-10-map/ns-gslb-bind-dom-vsvr-tsk.html>`_.

#. In each zone that are participating in GSLB, add GSLB-enabled
   NetScaler device.

   For more information, see :ref:`enabling-gslb-in-ns`.

As a domain administrator/ user perform the following:

#. Add a GSLB rule on both the sites.

   See ":ref:`adding-gslb-rule`".

#. Assign load balancer rules.

   See ":ref:`assigning-lb-rule-gslb`".


Prerequisites and Guidelines
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

-  The GSLB functionality is supported both Basic and Advanced zones.

-  GSLB is added as a new network service.

-  GSLB service provider can be added to a physical network in a zone.

-  The admin is allowed to enable or disable GSLB functionality at
   region level.

-  The admin is allowed to configure a zone as GSLB capable or enabled.

   A zone shall be considered as GSLB capable only if a GSLB service
   provider is provisioned in the zone.

-  When users have VMs deployed in multiple availability zones which are
   GSLB enabled, they can use the GSLB functionality to load balance
   traffic across the VMs in multiple zones.

-  The users can use GSLB to load balance across the VMs across zones in
   a region only if the admin has enabled GSLB in that region.

-  The users can load balance traffic across the availability zones in
   the same region or different regions.

-  The admin can configure DNS name for the entire cloud.

-  The users can specify an unique name across the cloud for a globally
   load balanced service. The provided name is used as the domain name
   under the DNS name associated with the cloud.

   The user-provided name along with the admin-provided DNS name is used
   to produce a globally resolvable FQDN for the globally load balanced
   service of the user. For example, if the admin has configured
   xyztelco.com as the DNS name for the cloud, and user specifies 'foo'
   for the GSLB virtual service, then the FQDN name of the GSLB virtual
   service is foo.xyztelco.com.

-  While setting up GSLB, users can select a load balancing method, such
   as round robin, for using across the zones that are part of GSLB.

-  The user shall be able to set weight to zone-level virtual server.
   Weight shall be considered by the load balancing method for
   distributing the traffic.

-  The GSLB functionality shall support session persistence, where
   series of client requests for particular domain name is sent to a
   virtual server on the same zone.

   Statistics is collected from each GSLB virtual server.


.. _enabling-gslb-in-ns:

Enabling GSLB in NetScaler
^^^^^^^^^^^^^^^^^^^^^^^^^^

In each zone, add GSLB-enabled NetScaler device for load balancing.

#. Log in as administrator to the CloudStack UI.

#. In the left navigation bar, click Infrastructure.

#. In Zones, click View More.

#. Choose the zone you want to work with.

#. Click the Physical Network tab, then click the name of the physical
   network.

#. In the Network Service Providers node of the diagram, click
   Configure.

   You might have to scroll down to see this.

#. Click NetScaler.

#. Click Add NetScaler device and provide the following:

   For NetScaler:

   -  **IP Address**: The IP address of the SDX.

   -  **Username/Password**: The authentication credentials to access
      the device. CloudStack uses these credentials to access the
      device.

   -  **Type**: The type of device that is being added. It could be F5
      Big Ip Load Balancer, NetScaler VPX, NetScaler MPX, or NetScaler
      SDX. For a comparison of the NetScaler types, see the CloudStack
      Administration Guide.

   -  **Public interface**: Interface of device that is configured to be
      part of the public network.

   -  **Private interface**: Interface of device that is configured to
      be part of the private network.

   -  **GSLB service**: Select this option.

   -  **GSLB service Public IP**: The public IP address of the NAT
      translator for a GSLB service that is on a private network.

   -  **GSLB service Private IP**: The private IP of the GSLB service.

   -  **Number of Retries**. Number of times to attempt a command on the
      device before considering the operation failed. Default is 2.

   -  **Capacity**: The number of networks the device can handle.

   -  **Dedicated**: When marked as dedicated, this device will be
      dedicated to a single account. When Dedicated is checked, the
      value in the Capacity field has no significance implicitly, its
      value is 1.

#. Click OK.


.. _adding-gslb-rule:

Adding a GSLB Rule
^^^^^^^^^^^^^^^^^^

#. Log in to the CloudStack UI as a domain administrator or user.

#. In the left navigation pane, click Region.

#. Select the region for which you want to create a GSLB rule.

#. In the Details tab, click View GSLB.

#. Click Add GSLB.

   The Add GSLB page is displayed as follows:

   |gslb-add.png|

#. Specify the following:

   -  **Name**: Name for the GSLB rule.

   -  **Description**: (Optional) A short description of the GSLB rule
      that can be displayed to users.

   -  **GSLB Domain Name**: A preferred domain name for the service.

   -  **Algorithm**: (Optional) The algorithm to use to load balance the
      traffic across the zones. The options are Round Robin, Least
      Connection, and Proximity.

   -  **Service Type**: The transport protocol to use for GSLB. The
      options are TCP and UDP.

   -  **Domain**: (Optional) The domain for which you want to create the
      GSLB rule.

   -  **Account**: (Optional) The account on which you want to apply the
      GSLB rule.

#. Click OK to confirm.


.. _assigning-lb-rule-gslb:

Assigning Load Balancing Rules to GSLB
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

#. Log in to the CloudStack UI as a domain administrator or user.

#. In the left navigation pane, click Region.

#. Select the region for which you want to create a GSLB rule.

#. In the Details tab, click View GSLB.

#. Select the desired GSLB.

#. Click view assigned load balancing.

#. Click assign more load balancing.

#. Select the load balancing rule you have created for the zone.

#. Click OK to confirm.


Known Limitation
~~~~~~~~~~~~~~~~

Currently, CloudStack does not support orchestration of services across
the zones. The notion of services and service providers in region are to
be introduced.


.. |gslb.png| image:: /_static/images/gslb.png
   :alt: GSLB architecture
.. |gslb-add.png| image:: /_static/images/add-gslb.png
   :alt: adding a gslb rule.