Overview

The definition of a SLA typically represents a contractual service commitment, describing the minimum performance criteria to meet while delivering a service. In this context the SLA element provides the means to specify low and high limits (defining an acceptable range) for a SLA with a given identifier. Additionally the SLA provides a mechanism to associate a SLA policy handler, which can be used to process policies specific to SLAs as they occur, taking specific actions appropriate for the ServiceBean.

SLA Policy Handlers

The Service Grid provides 3 SLA policy handlers. Additional policy handlers can be created by extending the policy handler class.

When a SeviceBean is instantiated by a GSC, the SLA element's ID is used to match a Watch that has been created by the ServiceBean, or declaratively created. If the SLA ID cannot be matched to a watch, the SLA will not be associated.

Once associated the SLAPolicyHandler will be notified based on the thresholds that have been set.

Sample SLA Declaration

An example SLA declaration follows:

<SLA ID="backlog" Low="100" High="500">
    <PolicyHandler type="scaling" max="10"
                   lowerDampener="3000" upperDampener="3000"/>
</SLA>

This SLA declares that a scaling policy handler be attached to a watch with the name of "backlog", that the number of services scale up to 10. This declaration also inlcudes lowerDampener and upperDampener configuration. The lowerDampener and upperDampener attributes have to do with the avoidance of oscillating around a threshold which is breached. These values behave as a smoothing filter, taking into account the reality that action on a threshold breach may need to be delayed.

Behavior if Type is Relocation or Notify

• If the "type' is either relocation or notify, the max attribute is ignored.
• If the type is notify, the lowerDampener and upperDampener attributes are ignored.

Matching SLA to Watch

The SLA is not always tied to the SLA ID attribute for matching up to a Watch. By declaring the <Monitor> element within the scope of the <SLA> element, a Watch will be dynamically added, using the declared attributes to obtain the information needed to observe the declared SLA thresholds. The SLA will be associated to the name of the <Monitor> (which is a Watch). This is illustrated here:

<SLA ID="backlog" Low="100" High="500">
    <PolicyHandler type="scaling" max="10"
                   lowerDampener="3000" upperDampener="3000"/>
    <Monitor name="collector" property="count" period="5000/
</SLA>

The Monitor declaration tells the Service Grid runtime to create and register a watch with the name of "collector", reading the getCount method every 5 seconds.

If the Watch already exists in the bean's WatchRegistry, the watch will not be added.

Java Bean Getter Method

The bean must declare a Java bean getter method that has as it's return type one of the following:

• Supported primitive types: int.class, long.class, float.class, double.class
• Supported types: Integer.class, Long.class, Lloat.class, Double.class

The read property return type is verified prior to watch creation. For example, given a bean called Foo, which declares a method called getCollector :

public class Foo {
    ...
    public long getCollector() {
        return(value);
    }
    ...
}

Defining Custom SLA Watcher

If you need to create a custom SLA watcher, use the Watch capability from the Rio project. The best way to do this with the M2 release is to use the Rio ServiceBean model.

The next release will allow injection of the ServiceBeanContext to a POJO if desired.

1. Based on the type of item you are watching, create one of the following:
   • A CounterWatch – counts a monotonically-increasing non-negative value of an arbitrary occurance of something over time.
   • A GaugeWatch – records values that can go up and down, and can be positive or negative.
   • A StopWatch – used for capturing elapsed time.
     The following code snippet illustrates this:

     GaugeWatch sampleWatcher = new GaugeWatch("metric");
     watchRegistry.register(sampleWatcher);

2. In the Deployment Descriptor, declare an SLA as follows:

   <ServiceLevelAgreements>
   	<SLA ID="metric" Low="100" High="500" >
   		<Configuration>
   		...
   		</Configuration>
   	</SLA>
   </ServiceLevelAgreements>

RELATED TOPICS

Declaring Elements Globally in Deployment Descriptor

Declaring Service UI in Deployment Descriptor

Deployment Descriptor Codebase Element

Deployment Descriptor DeploymentSchedule Element

Deployment Descriptor Parameters and Configuration Elements

Deployment Descriptor SharedComponent Element

Deployment Descriptor SLA Element

deploy - Service Grid CLI

Fixed and Dynamic ServiceBean ProvisionType

Injecting Deployment Descriptor Properties into POJOs

POJO Lifecycle in Service Grid

Proactive Cache

redeploy - Service Grid CLI

Rio OperationalString

Service Associations

Service Deployment Descriptor

Service Grid ClassLoader Hierarchy

undeploy - Service Grid CLI

Using Service Grid to Deploy Partitioned Space

Using Service Grid to Deploy Partitioned Space with Backup

Using Service Grid to Deploy Replicated Space

Using Service Grid to Deploy Space

Using Service Grid to Deploy Spring Applications

Using System Properties for Deployment Descriptor Element Values