Understanding Amazon EMR node allocation strategy and scenarios - Amazon EMR
Node allocation strategyNode allocation considerations Node allocation scenarios

Understanding Amazon EMR node allocation strategy and scenarios

This section gives an overview of node allocation strategy and common scaling scenarios that you can use with Amazon EMR managed scaling.

Node allocation strategy

Amazon EMR managed scaling allocates core and task nodes based on the following scale-up and scale-down strategies:

Scale-up strategy

  • For Amazon EMR releases 7.2 and higher, managed scaling first adds nodes based on node labels and the application process restriction YARN property.

  • For Amazon EMR releases 7.2 and higher, if you enabled node labels and restricted application processes to CORE nodes, Amazon EMR managed scaling scales up core nodes and task nodes if application process demand increases and executor demand increases. Similarly, if you enabled node labels and restricted application processes to ON_DEMAND nodes, managed scaling scales up on-demand nodes if application process demand increases and scales up spot nodes if executor demand increases.

  • If node labels aren't enabled, application process placement aren't restricted to any node or market type.

  • By using node labels, managed scaling can scale up and scale down different instance groups and instance fleets in the same resize operation. For example, in a scenario in which instance_group1 has ON_DEMAND node and instance_group2 has a SPOT node, and node labels are enabled and application processes are restricted to nodes with the ON_DEMAND label. Managed scaling will scale down instance_group1 and scale up instance_group2 if application process demand decreases and executor demand increases.

  • When Amazon EMR experiences a delay in scale-up with the current instance group, clusters that use managed scaling automatically switch to a different task instance group.

  • If the MaximumCoreCapacityUnits parameter is set, then Amazon EMR scales core nodes until the core units reach the maximum allowed limit. All the remaining capacity is added to task nodes.

  • If the MaximumOnDemandCapacityUnits parameter is set, then Amazon EMR scales the cluster by using the On-Demand Instances until the On-Demand units reach the maximum allowed limit. All the remaining capacity is added using Spot Instances.

  • If both the MaximumCoreCapacityUnits and MaximumOnDemandCapacityUnits parameters are set, Amazon EMR considers both limits during scaling.

    For example, if the MaximumCoreCapacityUnits is less than MaximumOnDemandCapacityUnits, Amazon EMR first scales core nodes until the core capacity limit is reached. For the remaining capacity, Amazon EMR first uses On-Demand Instances to scale task nodes until the On-Demand limit is reached, and then uses Spot Instances for task nodes.

Scale-down strategy

  • Similar to the scale-up strategy, Amazon EMR removes nodes based on node labels. For more information about node labels, see Understand node types: primary, core, and task nodes.

  • If you haven't enabled node labels, managed scaling removes task nodes and then removes core nodes until it achieves the desired scale-down target capacity. Managed scaling never scales down the cluster below the minimum constraints specified in the managed scaling policy.

  • Amazon EMR versions 5.34.0 and higher, and Amazon EMR versions 6.4.0 and higher, support managed scaling that is aware of Spark shuffle data (data that Spark redistributes across partitions to perform specific operations). For more information on shuffle operations, see the Spark Programming Guide. Managed scaling scales-down only instances that are under-utilized and which do not contain actively used shuffle data. This intelligent scaling prevents unintended shuffle data loss, avoiding the need for job re-attempts and recomputation of intermediate data.

  • Managed scaling first removes task nodes and then removes core nodes until it achieves the desired scale-down target capacity. The cluster never scales below the minimum constraints specified in the managed scaling policy.

  • For clusters that are launched with Amazon EMR 5.x releases 5.34.0 and higher, and 6.x releases 6.4.0 and higher, Amazon EMR-managed scaling doesn’t scale down nodes that have ApplicationMaster for Apache Spark running on them. This minimizes job failures and retries, which helps to improve job performance and reduce costs. To confirm which nodes in your cluster are running ApplicationMaster, visit the Spark History Server and filter for the driver under the Executors tab of your Spark application ID.

If the cluster does not have any load, then Amazon EMR cancels the addition of new instances from a previous evaluation and performs scale-down operations. If the cluster has a heavy load, Amazon EMR cancels the removal of instances and performs scale-up operations.

Node allocation considerations

We recommend that you use the On-Demand purchasing option for core nodes to avoid HDFS data loss in case of Spot reclamation. You can use the Spot purchasing option for task nodes to reduce costs and get faster job execution when more Spot Instances are added to task nodes.

Node allocation scenarios

You can create various scaling scenarios based on your needs by setting up the Maximum, Minimum, On-Demand limit, and Maximum core node parameters in different combinations.

Scenario 1: Scale Core Nodes Only

To scale core nodes only, the managed scaling parameters must meet the following requirements:

  • The On-Demand limit is equal to the maximum boundary.

  • The maximum core node is equal to the maximum boundary.

When the On-Demand limit and the maximum core node parameters are not specified, both parameters default to the maximum boundary.

This scenario isn't applicable if you use managed scaling with node labels and restrict your application processes to only run on CORE nodes, because managed scaling scales task nodes to accommodate executor demand.

The following examples demonstrate the scenario of scaling cores nodes only.

Cluster initial state Scaling parameters Scaling behavior

Instance groups

Core: 1 On-Demand

Task: 1 On-Demand and 1 Spot

UnitType: Instances

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 20

MaximumCoreCapacityUnits: 20

Scale between 1 to 20 Instances or instance fleet units on core nodes using On-Demand type. No scaling on task nodes.

When you use managed scaling with node labels and restrict your application proccesses to ON_DEMAND nodes, the cluster will scale 1 to 20 instances or instance fleet units on CORE nodes using the On-Demand or Spot type, depending on the type of demand.

Instance fleets

Core: 1 On-Demand

Task: 1 On-Demand and 1 Spot

UnitType: InstanceFleetUnits

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 20

MaximumCoreCapacityUnits: 20

Scenario 2: Scale task nodes only

To scale task nodes only, the managed scaling parameters must meet the following requirement:

  • The maximum core node must be equal to the minimum boundary.

The following examples demonstrate the scenario of scaling task nodes only.

Cluster initial state Scaling parameters Scaling behavior

Instance groups

Core: 2 On-Demand

Task: 1 Spot

UnitType: Instances

MinimumCapacityUnits: 2

MaximumCapacityUnits: 20

MaximumCoreCapacityUnits: 2

Keep core nodes steady at 2 and only scale task nodes between 0 to 18 instances or instance fleet units. The capacity between minimum and maximum boundaries is added to the task nodes only.

When you use managed scaling with node labels and restrict your application proccesses to ON_DEMAND nodes, the cluster will keep core nodes steady at 2 and only scale task nodes between 0 to 18 instances or instance fleet units that use the On-demand or Spot type, depending on the type of demand.

Instance fleets

Core: 2 On-Demand

Task: 1 Spot

UnitType: InstanceFleetUnits

MinimumCapacityUnits: 2

MaximumCapacityUnits: 20

MaximumCoreCapacityUnits: 2

Scenario 3: Only On-Demand Instances in the cluster

To have On-Demand Instances only, your cluster and the managed scaling parameters must meet the following requirement:

  • The On-Demand limit is equal to the maximum boundary.

    When the On-Demand limit is not specified, the parameter value defaults to the maximum boundary. The default value indicates that Amazon EMR scales On-Demand Instances only.

If the maximum core node is less than the maximum boundary, the maximum core node parameter can be used to split capacity allocation between core and task nodes.

To enable this scenario in a cluster composed of instance groups, all node groups in the cluster must use the On-Demand market type during initial configuration.

This scenario is not applicable if you use managed scaling with node labels and restrict your application processes to only run on ON_DEMAND nodes, because managed scaling scales Spot nodes to accommodate executor demand.

The following examples demonstrate the scenario of having On-Demand Instances in the entire cluster.

Cluster initial state Scaling parameters Scaling behavior

Instance groups

Core: 1 On-Demand

Task: 1 On-Demand

UnitType: Instances

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 20

MaximumCoreCapacityUnits: 12

Scale between 1 to 12 instances or instance fleet units on core nodes using On-Demand type. Scale the remaining capacity using On-Demand on task nodes. No scaling using Spot Instances.

When you use managed scaling with node labels and restrict your application proccesses to CORE nodes, the cluster scales between 1 to 20 instances or instance fleet units on CORE nodes or task nodes using the ON_DEMANDtype, depending on the type of demand. Scaling on core nodes will not exceed 12 instances or instance fleet units.

Instance fleets

Core: 1 On-Demand

Task: 1 On-Demand

UnitType: InstanceFleetUnits

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 20

MaximumCoreCapacityUnits: 12

Scenario 4: Only Spot Instances in the cluster

To have Spot Instances only, the managed scaling parameters must meet the following requirement:

  • On-Demand limit is set to 0.

If the maximum core node is less than the maximum boundary, the maximum core node parameter can be used to split capacity allocation between core and task nodes.

To enable this scenario in a cluster composed of instance groups, the core instance group must use the Spot purchasing option during initial configuration. If there is no Spot Instance in the task instance group, Amazon EMR managed scaling creates a task group using Spot Instances when needed.

This scenario isn't applicable if you use managed scaling with node labels and restrict your application processes to only run on ON_DEMAND nodes, because managed scaling scales ON_DEMAND nodes to accommodate application process demand.

The following examples demonstrate the scenario of having Spot Instances in the entire cluster.

Cluster initial state Scaling parameters Scaling behavior

Instance groups

Core: 1 Spot

Task: 1 Spot

UnitType: Instances

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 0

Scale between 1 to 20 instances or instance fleet units on core nodes using Spot. No scaling using On-Demand type.

When you use managed scaling with node labels and restrict your application proccesses to CORE nodes, the cluster scales between 1 to 20 instances or instance fleet units on CORE or TASK nodes using Spot, depending on the type of demand. Amazon EMR doesn't scale using the ON_DEMAND type.

Instance fleets

Core: 1 Spot

Task: 1 Spot

UnitType: InstanceFleetUnits

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 0

Scenario 5: Scale On-Demand Instances on core nodes and Spot Instances on task nodes

To scale On-Demand Instances on core nodes and Spot Instances on task nodes, the managed scaling parameters must meet the following requirements:

  • The On-Demand limit must be equal to the maximum core node.

  • Both the On-Demand limit and the maximum core node must be less than the maximum boundary.

To enable this scenario in a cluster composed of instance groups, the core node group must use the On-Demand purchasing option.

This scenario isn't applicable if you use managed scaling with node labels and restrict your application processes to only run on ON_DEMAND nodes or CORE nodes.

The following examples demonstrate the scenario of scaling On-Demand Instances on core nodes and Spot Instances on task nodes.

Cluster initial state Scaling parameters Scaling behavior

Instance groups

Core: 1 On-Demand

Task: 1 On-Demand and 1 Spot

UnitType: Instances

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 7

MaximumCoreCapacityUnits: 7

Scale up to 6 On-Demand units on the core node since there is already 1 On-Demand unit on the task node and the maximum limit for On-Demand is 7. Then scale up to 13 Spot units on task nodes.

Instance fleets

Core: 1 On-Demand

Task: 1 On-Demand and 1 Spot

UnitType: InstanceFleetUnits

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 7

MaximumCoreCapacityUnits: 7

Scenario 6: Scale CORE instances for application process demand and TASK instances for executor demand.

This scenario is only applicable if you use managed scaling with node labels and restrict application processes to only run on CORE nodes.

To scale CORE nodes based on application process demand and TASK nodes based on executor demand, you must set the following configurations at cluster launch:

  • yarn.node-labels.enabled:true

  • yarn.node-labels.am.default-node-label-expression: 'CORE'

If you don't specify the ON_DEMAND limit and the maximum CORE node parameters, both parameters default to the maximum boundary.

If the maximum ON_DEMAND node is less than the maximum boundary, managed scaling uses the maximum ON_DEMAND node parameter to split capacity allocation between ON_DEMAND and SPOT nodes. If you set the the maximum CORE node parameter to less than or equal to the minimum capacity parameter, CORE nodes remain static at the maximum core capacity.

The following examples demonstrate the scenario of scaling CORE instances based on application process demand and TASK instances based on executor demand.

Cluster initial state Scaling parameters Scaling behavior

Instance groups

Core: 1 On-Demand

Task: 1 On-Demand

UnitType: Instances

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 10

MaximumCoreCapacityUnits: 20

Scales CORE nodes between 1 and 20 nodes based on the cluster's application process demand using the On-Demand or Spot market type. Scales TASK nodes based on executor demand and remaining available capacity after Amazon EMR allocates CORE nodes.

The sum of requested CORE and TASK nodes won't exceed the maximumCapacity of 20. The sum of requested on-demand core nodes and on-demand task nodes won't exceed the maximumOnDemandCapacity of 10. Additional core or task nodes use the Spot market type.

Instance fleets

Core: 1 On-Demand

Task: 1 On-Demand

UnitType: InstanceFleetUnits

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 10

MaximumCoreCapacityUnits: 20

Scenario 7: Scale ON_DEMAND instances for application process demand and SPOT instances for executor demand.

This scenario is only applicable if you use managed scaling with node labels and restrict application processes to only run on ON_DEMAND nodes.

To scale ON_DEMAND nodes based on application process demand and SPOT nodes based on executor demand, you must set the following configurations at cluster launch:

  • yarn.node-labels.enabled:true

  • yarn.node-labels.am.default-node-label-expression: 'ON_DEMAND'

If you don't specify the ON_DEMAND limit and the maximum CORE node parameters, both parameters default to the maximum boundary.

If the maximum CORE node is less than the maximum boundary, managed scaling uses the maximum CORE node parameter to split capacity allocation between CORE and TASK nodes. If you set the the maximum CORE node parameter to less than or equal to the minimum capacity parameter, CORE nodes remain static at the maximum core capacity.

The following examples demonstrate the scenario of scaling On-Demand Instances based on application process demand and Spot instances based on executor demand.

Cluster initial state Scaling parameters Scaling behavior

Instance groups

Core: 1 On-Demand

Task: 1 On-Demand

UnitType: Instances

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 20

MaximumCoreCapacityUnits: 10

Scales ON_DEMAND nodes between 1 and 20 nodes based on the cluster's application process demand using the CORE or TASK node type. Scales SPOT nodes based on executor demand and remaining available capacity after Amazon EMR allocates ON_DEMAND nodes.

The sum of requested ON_DEMAND and SPOT nodes won't exceed the maximumCapacity of 20. The sum of requested on-demand core nodes and spot core nodes won't exceed the maximumCoreCapacity of 10. Additional on-demand or spot nodes use the TASK node type.

Instance fleets

Core: 1 On-Demand

Task: 1 On-Demand

UnitType: InstanceFleetUnits

MinimumCapacityUnits: 1

MaximumCapacityUnits: 20

MaximumOnDemandCapacityUnits: 20

MaximumCoreCapacityUnits: 10