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Chapter 16. Managing Networks and Traffic
162
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, in which the conditions that you specify for a scaleup action to
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,
CloudPlatform 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 CloudPlatform 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: