ESC is capable of elastically scaling the service. It can be configured to do both scale in and scale out automatically. The scaling is achieved using KPI, rules and actions. These are configured during deployment. The KPI define the event name and threshold. The rules define action to trigger scale out and scale in.

Scaling workflow begins after successful deployment of a VNF. VMs are configured to monitor attributes such as CPU load, memory usage, and so on, which form the KPI data in the data model. If for any attributes, KPI reaches its threshold, based on the action defined, scale in and scale out is performed.

• During scale out, if the number of VMs is less than maximum active, a new VM deployment is triggered.

• During scale in, if the number of VMs is greater than the minimum active, the VM will be undeployed.

Note	If the VM is deployed and did not receive the VM alive event, then recovery will be triggered. Any error during undeployment will be notified to the northbound user.

In the scaling section of the datamodel, the minimum and maximum values are configured. The min_active defines the number of VMs deployed. The max_active defines the number of maximum VMs that can be deployed. For example, if a VNF is deployed with a minimum 2 VMs and a maximum of 100 VMs, the below xml will define scaling under each VM group.

If the primary VM was configured using a static IP address, the scaled out VMs must be assigned a static IP address. During deployment, a list of static IP addresses must be specified. The following example explains how to create a static IP pool:

 <scaling>
   <min_active>1</min_active>
   <max_active>2</max_active>
   <elastic>true</elastic>
   <static_ip_address_pool>
      <network>1234-5678-9123</network>
      <gateway>10.86.22.1</gateway>
      <netmask>255.255.255.0</netmask>
      <ip_address>10.86.22.227</ip_address>
      <ip_address>10.86.22.228</ip_address>
   </static_ip_address_pool>
</scaling>

The following example explains the method of detecting the CPU load in the KPI data section.

<kpi>
          <event_name>VM_OVERLOADED</event_name>
          <metric_value>70</metric_value>
          <metric_cond>GT</metric_cond>
          <metric_type>UINT32</metric_type>
            <metric_occurrences_true>2</metric_occurrences_true>
            <metric_occurrences_false>4</metric_occurrences_false>
          <metric_collector>
          <type>CPU_LOAD_1</type>
          <nicid>0</nicid>
          <poll_frequency>3</poll_frequency>
          <polling_unit>seconds</polling_unit>
          <continuous_alarm>false</continuous_alarm>
          </metric_collector>
          </kpi>
        <kpi>
        <event_name>VM_UNDERLOADED</event_name>
        <metric_value>40</metric_value>
        <metric_cond>LT</metric_cond>
        <metric_type>UINT32</metric_type>
 <metric_occurrences_true>2</metric_occurrences_true>
 <metric_occurrences_false>4</metric_occurrences_false>
         <metric_collector>
         <type>CPU_LOAD_1</type>
         <nicid>0</nicid>
         <poll_frequency>3</poll_frequency>
         <polling_unit>seconds</polling_unit>
 	<continuous_alarm>false</continuous_alarm>
        </metric_collector>
        </kpi>

KPI rules are as follows:

<rule>
   <event_name>VM_OVERLOADED</event_name>
   <action>ALWAYS log</action>
   <action>TRUE servicescaleup.sh</action>
</rule>
<rule>
   <event_name>VM_UNDERLOADED</event_name>
   <action>ALWAYS log</action>
   <action>TRUE servicescaledown.sh</action>
</rule>

The scaling notifications are sent to the northbound users. The notification includes status message and other details to identify the service that is undergoing scaling. Below is the list of notifications:

VM_SCALE_OUT_INIT
VM_SCALE_OUT_DEPLOYED
VM_SCALE_OUT_COMPLETE
VM_SCALE_IN_INIT
VM_SCALE_IN_COMPLETE

The following table lists the scaling scenarios and the notifications that are generated:

<type>SERVICE_ALIVE</type>
<status>SUCCESS</status>

<type> VM_SCALE_OUT_INIT</type>
<status>SUCCESS</status>

<type> VM_SCALE_OUT_DEPLOYED</type>
<status>SUCCESS</status>

<type>VM_SCALE_OUT_COMPLETE</type>
 <status>SUCCESS</status>  

<type>SERVICE_ALIVE</type>
<status>SUCCESS</status>

<type> VM_SCALE_IN_INIT</type>
<status>SUCCESS</status>

<type>VM_SCALE_IN_COMPLETE</type> 
<status>SUCCESS</status>

For all the error scenarios, the notification will be sent with FAILURE status. Also status message should have the corresponding failure details.