.. Licensed to the Apache Software Foundation (ASF) under one
   or more contributor license agreements.  See the NOTICE file
   distributed with this work for additional information#
   regarding copyright ownership.  The ASF licenses this file
   to you under the Apache License, Version 2.0 (the
   "License"); you may not use this file except in compliance
   with the License.  You may obtain a copy of the License at
   http://www.apache.org/licenses/LICENSE-2.0
   Unless required by applicable law or agreed to in writing,
   software distributed under the License is distributed on an
   "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   KIND, either express or implied.  See the License for the
   specific language governing permissions and limitations
   under the License.


External Firewalls and Load Balancers
-------------------------------------

CloudStack is capable of replacing its Virtual Router with an external
Juniper SRX device and an optional external NetScaler or F5 load
balancer for gateway and load balancing services. In this case, the VMs
use the SRX as their gateway.


About Using a NetScaler Load Balancer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Citrix NetScaler is supported as an external network element for load
balancing in zones that use isolated networking in advanced zones. Set
up an external load balancer when you want to provide load balancing
through means other than CloudStack's provided virtual router.

.. note::
   In a Basic zone, load balancing service is supported only if
   Elastic IP or Elastic LB services are enabled.

When NetScaler load balancer is used to provide EIP or ELB services in a
Basic zone, ensure that all guest VM traffic must enter and exit through
the NetScaler device. When inbound traffic goes through the NetScaler
device, traffic is routed by using the NAT protocol depending on the
EIP/ELB configured on the public IP to the private IP. The traffic that
is originated from the guest VMs usually goes through the layer 3
router. To ensure that outbound traffic goes through NetScaler device
providing EIP/ELB, layer 3 router must have a policy-based routing. A
policy-based route must be set up so that all traffic originated from
the guest VM's are directed to NetScaler device. This is required to
ensure that the outbound traffic from the guest VM's is routed to a
public IP by using NAT.For more information on Elastic IP, see
`"About Elastic IP" <#about-elastic-ip>`_.

The NetScaler can be set up in direct (outside the firewall) mode. It
must be added before any load balancing rules are deployed on guest VMs
in the zone.

The functional behavior of the NetScaler with CloudStack is the same as
described in the CloudStack documentation for using an F5 external load
balancer. The only exception is that the F5 supports routing domains,
and NetScaler does not. NetScaler can not yet be used as a firewall.

To install and enable an external load balancer for CloudStack
management, see External Guest Load Balancer Integration in the
Installation Guide.

The Citrix NetScaler comes in three varieties. The following
summarizes how these variants are treated in CloudStack.

**MPX**

-  Physical appliance. Capable of deep packet inspection. Can act as
   application firewall and load balancer

-  In advanced zones, load balancer functionality fully supported without
   limitation. In basic zones, static NAT, elastic IP (EIP), and elastic
   load balancing (ELB) are also provided.

**VPX**

-  Virtual appliance. Can run as VM on XenServer, ESXi, and Hyper-V
   hypervisors. Same functionality as MPX

-  Supported on ESXi and XenServer. Same functional support as for MPX.
   CloudStack will treat VPX and MPX as the same device type.

**SDX**

-  Physical appliance. Can create multiple fully isolated VPX instances on
   a single appliance to support multi-tenant usage

-  CloudStack will dynamically provision, configure, and manage the life
   cycle of VPX instances on the SDX. Provisioned instances are added into
   CloudStack automatically - no manual configuration by the administrator
   is required. Once a VPX instance is added into CloudStack, it is treated
   the same as a VPX on an ESXi host.


Configuring SNMP Community String on a RHEL Server
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The SNMP Community string is similar to a user id or password that
provides access to a network device, such as router. This string is sent
along with all SNMP requests. If the community string is correct, the
device responds with the requested information. If the community string
is incorrect, the device discards the request and does not respond.

The NetScaler device uses SNMP to communicate with the VMs. You must
install SNMP and configure SNMP Community string for a secure
communication between the NetScaler device and the RHEL machine.

#. Ensure that you installed SNMP on RedHat. If not, run the following
   command:

   .. code:: bash

      yum install net-snmp-utils

#. Edit the /etc/snmp/snmpd.conf file to allow the SNMP polling from the
   NetScaler device.

   #. Map the community name into a security name (local and mynetwork,
      depending on where the request is coming from):

      .. note::
         Use a strong password instead of public when you edit the
         following table.

      .. code:: bash

         #         sec.name   source        community
         com2sec   local      localhost     public
         com2sec   mynetwork  0.0.0.0       public

      .. note:: Setting to 0.0.0.0 allows all IPs to poll the NetScaler server.

   #. Map the security names into group names:

      .. code:: bash

         #       group.name    sec.model  sec.name
         group   MyRWGroup     v1         local
         group   MyRWGroup     v2c        local
         group   MyROGroup     v1         mynetwork
         group   MyROGroup     v2c        mynetwork

   #. Create a view to allow the groups to have the permission to:

      .. code:: bash

         incl/excl subtree mask view all included .1

   #. Grant access with different write permissions to the two groups to
      the view you created.

      .. code:: bash

         # context     sec.model     sec.level      prefix     read     write    notif
           access      MyROGroup ""  any noauth     exact      all      none     none
           access      MyRWGroup ""  any noauth     exact      all      all      all

#. Unblock SNMP in iptables.

   .. code:: bash

      iptables -A INPUT -p udp --dport 161 -j ACCEPT

#. Start the SNMP service:

   .. code:: bash

      service snmpd start

#. Ensure that the SNMP service is started automatically during the
   system startup:

   .. code:: bash

      chkconfig snmpd on


Initial Setup of External Firewalls and Load Balancers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When the first VM is created for a new account, CloudStack programs the
external firewall and load balancer to work with the VM. The following
objects are created on the firewall:

-  A new logical interface to connect to the account's private VLAN. The
   interface IP is always the first IP of the account's private subnet
   (e.g. 10.1.1.1).

-  A source NAT rule that forwards all outgoing traffic from the
   account's private VLAN to the public Internet, using the account's
   public IP address as the source address

-  A firewall filter counter that measures the number of bytes of
   outgoing traffic for the account

The following objects are created on the load balancer:

-  A new VLAN that matches the account's provisioned Zone VLAN

-  A self IP for the VLAN. This is always the second IP of the account's
   private subnet (e.g. 10.1.1.2).


Ongoing Configuration of External Firewalls and Load Balancers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Additional user actions (e.g. setting a port forward) will cause further
programming of the firewall and load balancer. A user may request
additional public IP addresses and forward traffic received at these IPs
to specific VMs. This is accomplished by enabling static NAT for a
public IP address, assigning the IP to a VM, and specifying a set of
protocols and port ranges to open. When a static NAT rule is created,
CloudStack programs the zone's external firewall with the following
objects:

-  A static NAT rule that maps the public IP address to the private IP
   address of a VM.

-  A security policy that allows traffic within the set of protocols and
   port ranges that are specified.

-  A firewall filter counter that measures the number of bytes of
   incoming traffic to the public IP.

The number of incoming and outgoing bytes through source NAT, static
NAT, and load balancing rules is measured and saved on each external
element. This data is collected on a regular basis and stored in the
CloudStack database.


Load Balancer Rules
~~~~~~~~~~~~~~~~~~~

A CloudStack user or administrator may create load balancing rules that
balance traffic received at a public IP to one or more VMs. A user
creates a rule, specifies an algorithm, and assigns the rule to a set of
VMs.

.. note::
   If you create load balancing rules while using a network service
   offering that includes an external load balancer device such as
   NetScaler, and later change the network service offering to one that
   uses the CloudStack virtual router, you must create a firewall rule on
   the virtual router for each of your existing load balancing rules so
   that they continue to function.


.. _adding-lb-rule:

Adding a Load Balancer Rule
^^^^^^^^^^^^^^^^^^^^^^^^^^^

#. Log in to the CloudStack UI as an administrator or end user.

#. In the left navigation, choose Network.

#. Click the name of the network where you want to load balance the
   traffic.

#. Click Public IP Addresses.

#. Click the IP address for which you want to create the rule.

#. Click the Load Balancing tab.

   In a Basic zone, you can also create a load balancing rule without
   acquiring or selecting an IP address. CloudStack internally assign an
   IP when you create the load balancing rule, which is listed in the IP
   Addresses page when the rule is created.

   To do that, select the name of the network, then click Add Load
   Balancer tab. Continue with #7.

#. Fill in the following:

   -  **Name**: A name for the load balancer rule.

   -  **Public Port**: The port receiving incoming traffic to be
      balanced.

   -  **Private Port**: The port that the VMs will use to receive the
      traffic.

   -  **Algorithm**: Choose the load balancing algorithm you want
      CloudStack to use. CloudStack supports a variety of well-known
      algorithms. If you are not familiar with these choices, you will
      find plenty of information about them on the Internet.

   -  **Stickiness**: (Optional) Click Configure and choose the
      algorithm for the stickiness policy. See Sticky Session Policies
      for Load Balancer Rules.

   -  **AutoScale**: Click Configure and complete the AutoScale
      configuration as explained in :ref:`conf-autoscale`.

   -  **Health Check**: (Optional; NetScaler load balancers only) Click
      Configure and fill in the characteristics of the health check
      policy. See :ref:`health-check`.

      -  **Ping path (Optional)**: Sequence of destinations to which to
         send health check queries. Default: / (all).

      -  **Response time (Optional)**: How long to wait for a response
         from the health check (2 - 60 seconds). Default: 5 seconds.

      -  **Interval time (Optional)**: Amount of time between health
         checks (1 second - 5 minutes). Default value is set in the
         global configuration parameter lbrule\_health
         check\_time\_interval.

      -  **Healthy threshold (Optional)**: Number of consecutive health
         check successes that are required before declaring an instance
         healthy. Default: 2.

      -  **Unhealthy threshold (Optional)**: Number of consecutive
         health check failures that are required before declaring an
         instance unhealthy. Default: 10.

#. Click Add VMs, then select two or more VMs that will divide the load
   of incoming traffic, and click Apply.

   The new load balancer rule appears in the list. You can repeat these
   steps to add more load balancer rules for this IP address.


Sticky Session Policies for Load Balancer Rules
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Sticky sessions are used in Web-based applications to ensure continued
availability of information across the multiple requests in a user's
session. For example, if a shopper is filling a cart, you need to
remember what has been purchased so far. The concept of "stickiness" is
also referred to as persistence or maintaining state.

Any load balancer rule defined in CloudStack can have a stickiness
policy. The policy consists of a name, stickiness method, and
parameters. The parameters are name-value pairs or flags, which are
defined by the load balancer vendor. The stickiness method could be load
balancer-generated cookie, application-generated cookie, or
source-based. In the source-based method, the source IP address is used
to identify the user and locate the user's stored data. In the other
methods, cookies are used. The cookie generated by the load balancer or
application is included in request and response URLs to create
persistence. The cookie name can be specified by the administrator or
automatically generated. A variety of options are provided to control
the exact behavior of cookies, such as how they are generated and
whether they are cached.

For the most up to date list of available stickiness methods, see the
CloudStack UI or call listNetworks and check the
SupportedStickinessMethods capability.


.. _health-check:

Health Checks for Load Balancer Rules
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

(NetScaler load balancer only; requires NetScaler version 10.0)

Health checks are used in load-balanced applications to ensure that
requests are forwarded only to running, available services. When
creating a load balancer rule, you can specify a health check policy.
This is in addition to specifying the stickiness policy, algorithm, and
other load balancer rule options. You can configure one health check
policy per load balancer rule.

Any load balancer rule defined on a NetScaler load balancer in
CloudStack can have a health check policy. The policy consists of a ping
path, thresholds to define "healthy" and "unhealthy" states, health
check frequency, and timeout wait interval.

When a health check policy is in effect, the load balancer will stop
forwarding requests to any resources that are found to be unhealthy. If
the resource later becomes available again, the periodic health check
will discover it, and the resource will once again be added to the pool
of resources that can receive requests from the load balancer. At any
given time, the most recent result of the health check is displayed in
the UI. For any VM that is attached to a load balancer rule with a
health check configured, the state will be shown as UP or DOWN in the UI
depending on the result of the most recent health check.

You can delete or modify existing health check policies.

To configure how often the health check is performed by default, use the
global configuration setting healthcheck.update.interval (default value
is 600 seconds). You can override this value for an individual health
check policy.

For details on how to set a health check policy using the UI, see
:ref:`adding-lb-rule`.


.. _conf-autoscale:

Configuring AutoScale
~~~~~~~~~~~~~~~~~~~~~

AutoScaling allows you to scale your back-end services or application
VMs up or down seamlessly and automatically according to the conditions
you define. With AutoScaling enabled, you can ensure that the number of
VMs you are using seamlessly scale up when demand increases, and
automatically decreases when demand subsides. Thus it helps you save
compute costs by terminating underused VMs automatically and launching
new VMs when you need them, without the need for manual intervention.

NetScaler AutoScaling is designed to seamlessly launch or terminate VMs
based on user-defined conditions. Conditions for triggering a scaleup or
scaledown action can vary from a simple use case like monitoring the CPU
usage of a server to a complex use case of monitoring a combination of
server's responsiveness and its CPU usage. For example, you can
configure AutoScaling to launch an additional VM whenever CPU usage
exceeds 80 percent for 15 minutes, or to remove a VM whenever CPU usage
is less than 20 percent for 30 minutes.

CloudStack uses the NetScaler load balancer to monitor all aspects of a
system's health and work in unison with CloudStack to initiate scale-up
or scale-down actions.

.. note::
   AutoScale is supported on NetScaler Release 10 Build 74.4006.e and beyond.


Prerequisites
^^^^^^^^^^^^^

Before you configure an AutoScale rule, consider the following:

-  Ensure that the necessary template is prepared before configuring
   AutoScale. When a VM is deployed by using a template and when it
   comes up, the application should be up and running.

   .. note::
      If the application is not running, the NetScaler device considers the
      VM as ineffective and continues provisioning the VMs unconditionally
      until the resource limit is exhausted.

-  Deploy the templates you prepared. Ensure that the applications come
   up on the first boot and is ready to take the traffic. Observe the
   time requires to deploy the template. Consider this time when you
   specify the quiet time while configuring AutoScale.

-  The AutoScale feature supports the SNMP counters that can be used to
   define conditions for taking scale up or scale down actions. To
   monitor the SNMP-based counter, ensure that the SNMP agent is
   installed in the template used for creating the AutoScale VMs, and
   the SNMP operations work with the configured SNMP community and port
   by using standard SNMP managers. For example, see
   `"Configuring SNMP Community String on a RHELServer"
   <#configuring-snmp-community-string-on-a-rhel-server>`_
   to configure SNMP on a RHEL machine.

-  Ensure that the endpointe.url parameter present in the Global
   Settings is set to the Management Server API URL. For example,
   ``http://10.102.102.22:8080/client/api``. In a multi-node Management
   Server deployment, use the virtual IP address configured in the load
   balancer for the management server's cluster. Additionally, ensure
   that the NetScaler device has access to this IP address to provide
   AutoScale support.

   If you update the endpointe.url, disable the AutoScale functionality
   of the load balancer rules in the system, then enable them back to
   reflect the changes. For more information see :ref:`update-autoscale`.

-  If the API Key and Secret Key are regenerated for an AutoScale user,
   ensure that the AutoScale functionality of the load balancers that
   the user participates in are disabled and then enabled to reflect the
   configuration changes in the NetScaler.

-  In an advanced Zone, ensure that at least one VM should be present
   before configuring a load balancer rule with AutoScale. Having one VM
   in the network ensures that the network is in implemented state for
   configuring AutoScale.


Configuration
^^^^^^^^^^^^^

Specify the following:

|autoscaleateconfig.png|

-  **Template**: A template consists of a base OS image and application.
   A template is used to provision the new instance of an application on
   a scaleup action. When a VM is deployed from a template, the VM can
   start taking the traffic from the load balancer without any admin
   intervention. For example, if the VM is deployed for a Web service,
   it should have the Web server running, the database connected, and so
   on.

-  **Compute offering**: A predefined set of virtual hardware
   attributes, including CPU speed, number of CPUs, and RAM size, that
   the user can select when creating a new virtual machine instance.
   Choose one of the compute offerings to be used while provisioning a
   VM instance as part of scaleup action.

-  **Min Instance**: The minimum number of active VM instances that is
   assigned to a load balancing rule. The active VM instances are the
   application instances that are up and serving the traffic, and are
   being load balanced. This parameter ensures that a load balancing
   rule has at least the configured number of active VM instances are
   available to serve the traffic.

   .. note::
      If an application, such as SAP, running on a VM instance is down for
      some reason, the VM is then not counted as part of Min Instance
      parameter, and the AutoScale feature initiates a scaleup action if
      the number of active VM instances is below the configured value.
      Similarly, when an application instance comes up from its earlier
      down state, this application instance is counted as part of the
      active instance count and the AutoScale process initiates a scaledown
      action when the active instance count breaches the Max instance
      value.

-  **Max Instance**: Maximum number of active VM instances that **should
   be assigned to**\ a load balancing rule. This parameter defines the
   upper limit of active VM instances that can be assigned to a load
   balancing rule.

   Specifying a large value for the maximum instance parameter might
   result in provisioning large number of VM instances, which in turn
   leads to a single load balancing rule exhausting the VM instances
   limit specified at the account or domain level.

   .. note::
      If an application, such as SAP, running on a VM instance is down for
      some reason, the VM is not counted as part of Max Instance parameter.
      So there may be scenarios where the number of VMs provisioned for a
      scaleup action might be more than the configured Max Instance value.
      Once the application instances in the VMs are up from an earlier down
      state, the AutoScale feature starts aligning to the configured Max
      Instance value.

Specify the following scale-up and scale-down policies:

-  **Duration**: The duration, in seconds, for which the conditions you
   specify must be true to trigger a scaleup action. The conditions
   defined should hold true for the entire duration you specify for an
   AutoScale action to be invoked.

-  **Counter**: The performance counters expose the state of the
   monitored instances. By default, CloudStack offers four performance
   counters: Three SNMP counters and one NetScaler counter. The SNMP
   counters are Linux User CPU, Linux System CPU, and Linux CPU Idle.
   The NetScaler counter is ResponseTime. The root administrator can add
   additional counters into CloudStack by using the CloudStack API.

-  **Operator**: The following five relational operators are supported
   in AutoScale feature: Greater than, Less than, Less than or equal to,
   Greater than or equal to, and Equal to.

-  **Threshold**: Threshold value to be used for the counter. Once the
   counter defined above breaches the threshold value, the AutoScale
   feature initiates a scaleup or scaledown action.

-  **Add**: Click Add to add the condition.

Additionally, if you want to configure the advanced settings, click Show
advanced settings, and specify the following:

-  **Polling interval**: Frequency in which the conditions, combination
   of counter, operator and threshold, are to be evaluated before taking
   a scale up or down action. The default polling interval is 30
   seconds.

-  **Quiet Time**: This is the cool down period after an AutoScale
   action is initiated. The time includes the time taken to complete
   provisioning a VM instance from its template and the time taken by an
   application to be ready to serve traffic. This quiet time allows the
   fleet to come up to a stable state before any action can take place.
   The default is 300 seconds.

-  **Destroy VM Grace Period**: The duration in seconds, after a
   scaledown action is initiated, to wait before the VM is destroyed as
   part of scaledown action. This is to ensure graceful close of any
   pending sessions or transactions being served by the VM marked for
   destroy. The default is 120 seconds.

-  **Security Groups**: Security groups provide a way to isolate traffic
   to the VM instances. A security group is a group of VMs that filter
   their incoming and outgoing traffic according to a set of rules,
   called ingress and egress rules. These rules filter network traffic
   according to the IP address that is attempting to communicate with
   the VM.

-  **Disk Offerings**: A predefined set of disk size for primary data
   storage.

-  **SNMP Community**: The SNMP community string to be used by the
   NetScaler device to query the configured counter value from the
   provisioned VM instances. Default is public.

-  **SNMP Port**: The port number on which the SNMP agent that run on
   the provisioned VMs is listening. Default port is 161.

-  **User**: This is the user that the NetScaler device use to invoke
   scaleup and scaledown API calls to the cloud. If no option is
   specified, the user who configures AutoScaling is applied. Specify
   another user name to override.

-  **Apply**: Click Apply to create the AutoScale configuration.


Disabling and Enabling an AutoScale Configuration
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If you want to perform any maintenance operation on the AutoScale VM
instances, disable the AutoScale configuration. When the AutoScale
configuration is disabled, no scaleup or scaledown action is performed.
You can use this downtime for the maintenance activities. To disable the
AutoScale configuration, click the Disable AutoScale |EnableDisable.png| button.

The button toggles between enable and disable, depending on whether
AutoScale is currently enabled or not. After the maintenance operations
are done, you can enable the AutoScale configuration back. To enable,
open the AutoScale configuration page again, then click the Enable
AutoScale |EnableDisable.png| button.


.. _update-autoscale:

Updating an AutoScale Configuration
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You can update the various parameters and add or delete the conditions
in a scaleup or scaledown rule. Before you update an AutoScale
configuration, ensure that you disable the AutoScale load balancer rule
by clicking the Disable AutoScale button.

After you modify the required AutoScale parameters, click Apply. To
apply the new AutoScale policies, open the AutoScale configuration page
again, then click the Enable AutoScale button.


Runtime Considerations
^^^^^^^^^^^^^^^^^^^^^^

-  An administrator should not assign a VM to a load balancing rule
   which is configured for AutoScale.

-  Before a VM provisioning is completed if NetScaler is shutdown or
   restarted, the provisioned VM cannot be a part of the load balancing
   rule though the intent was to assign it to a load balancing rule. To
   workaround, rename the AutoScale provisioned VMs based on the rule
   name or ID so at any point of time the VMs can be reconciled to its
   load balancing rule.

-  Making API calls outside the context of AutoScale, such as destroyVM,
   on an autoscaled VM leaves the load balancing configuration in an
   inconsistent state. Though VM is destroyed from the load balancer
   rule, NetScaler continues to show the VM as a service assigned to a
   rule.


.. |autoscaleateconfig.png| image:: /_static/images/autoscale-config.png
   :alt: Configuring AutoScale.
.. |EnableDisable.png| image:: /_static/images/enable-disable-autoscale.png
   :alt: button to enable or disable AutoScale.