com.netflix.fenzo.plugins

Class BalancedHostAttrConstraint

java.lang.Object

com.netflix.fenzo.plugins.BalancedHostAttrConstraint

All Implemented Interfaces:

ConstraintEvaluator

public class BalancedHostAttrConstraint
extends java.lang.Object
implements ConstraintEvaluator

A balanced host attribute constraint attempts to distribute co-tasks evenly among host types, where their types are determined by the values of particular host attributes.

Nested Class Summary

Nested classes/interfaces inherited from interface com.netflix.fenzo.ConstraintEvaluator

ConstraintEvaluator.Result

Constructor Summary

Constructors

Constructor and Description
BalancedHostAttrConstraint(Func1<java.lang.String,java.util.Set<java.lang.String>> coTasksGetter, java.lang.String hostAttributeName, int expectedValues) Create a constraint evaluator to balance tasks across hosts based on a given host attribute.

Method Summary

Modifier and Type	Method and Description
VMTaskFitnessCalculator	asSoftConstraint() Converts this constraint into a "soft" constraint.
ConstraintEvaluator.Result	evaluate(TaskRequest taskRequest, VirtualMachineCurrentState targetVM, TaskTrackerState taskTrackerState) Inspects a target to decide whether or not it meets the constraints appropriate to a particular task.
java.lang.String	getName() Returns the name of the balanced host attribute constraint, which takes the form of the name of the class (or subclass) followed by a dash followed by the value of hostAttributeName as it was set when the constraint object was created.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BalancedHostAttrConstraint

public BalancedHostAttrConstraint(Func1<java.lang.String,java.util.Set<java.lang.String>> coTasksGetter,
                                  java.lang.String hostAttributeName,
                                  int expectedValues)

Create a constraint evaluator to balance tasks across hosts based on a given host attribute. For example, if ten hosts have three distinct host attribute values between them of A, B, and C, when nine tasks are scheduled, three tasks are assigned to hosts with attribute value A, another three tasks to hosts with attribute B, and so on.

Parameters:

coTasksGetter - a one-argument function that, given a task ID being considered for assignment, returns the set of Task IDs of the tasks that form the group of tasks which need to be balanced

hostAttributeName - the name of the host attribute whose values need to be balanced across the co-tasks

expectedValues - the number of distinct values to expect for hostAttributeName

Method Detail

getName

public java.lang.String getName()

Returns the name of the balanced host attribute constraint, which takes the form of the name of the class (or subclass) followed by a dash followed by the value of hostAttributeName as it was set when the constraint object was created.

Specified by:

getName in interface ConstraintEvaluator

Returns:

the name of the balanced host attribute constraint

evaluate

public ConstraintEvaluator.Result evaluate(TaskRequest taskRequest,
                                           VirtualMachineCurrentState targetVM,
                                           TaskTrackerState taskTrackerState)

Description copied from interface: ConstraintEvaluator

Inspects a target to decide whether or not it meets the constraints appropriate to a particular task.

Specified by:

evaluate in interface ConstraintEvaluator

Parameters:

taskRequest - a description of the task to be assigned

targetVM - a description of the host that is a potential match for the task

taskTrackerState - the current status of tasks and task assignments in the system at large

Returns:

a successful Result if the target meets the constraints enforced by this constraint evaluator, or an unsuccessful Result otherwise

asSoftConstraint

public VMTaskFitnessCalculator asSoftConstraint()

Converts this constraint into a "soft" constraint. By default, a balanced host attribute constraint is a "hard" constraint, which is to say that Fenzo will guarantee that the constraint is applied and will fail to place a task if the only way it can do so is to violate the constraint. This method returns a VMTaskFitnessCalculator that represents this constraint as a "soft" constraint that will permit Fenzo to place a task in violation of the constraint if it cannot do so otherwise.

Returns:

a task fitness calculator that represents the balanced host attribute constraint as a soft constraint