Understanding managed scaling metrics

Amazon EMR publishes high-resolution metrics with data at a one-minute granularity when managed scaling is enabled for a cluster. You can view events on every resize initiation and completion controlled by managed scaling with the Amazon EMR console or the Amazon CloudWatch console. CloudWatch metrics are critical for Amazon EMR managed scaling to operate. We recommend that you closely monitor CloudWatch metrics to make sure data is not missing. For more information about how you can configure CloudWatch alarms to detect missing metrics, see Using Amazon CloudWatch alarms. For more information about using CloudWatch events with Amazon EMR, see Monitor CloudWatch events.

The following metrics indicate the current or target capacities of a cluster. These metrics are only available when managed scaling is enabled. For clusters composed of instance fleets, the cluster capacity metrics are measured in Units. For clusters composed of instance groups, the cluster capacity metrics are measured in Nodes or vCPU based on the unit type used in the managed scaling policy.

Metric	Description
TotalUnitsRequested TotalNodesRequested TotalVCPURequested	The target total number of units/nodes/vCPUs in a cluster as determined by managed scaling. Units: Count
TotalUnitsRunning TotalNodesRunning TotalVCPURunning	The current total number of units/nodes/vCPUs available in a running cluster. When a cluster resize is requested, this metric will be updated after the new instances are added or removed from the cluster. Units: Count
CoreUnitsRequested CoreNodesRequested CoreVCPURequested	The target number of CORE units/nodes/vCPUs in a cluster as determined by managed scaling. Units: Count
CoreUnitsRunning CoreNodesRunning CoreVCPURunning	The current number of CORE units/nodes/vCPUs running in a cluster. Units: Count
TaskUnitsRequested TaskNodesRequested TaskVCPURequested	The target number of TASK units/nodes/vCPUs in a cluster as determined by managed scaling. Units: Count
TaskUnitsRunning TaskNodesRunning TaskVCPURunning	The current number of TASK units/nodes/vCPUs running in a cluster. Units: Count

The following metrics indicate the usage status of cluster and applications. These metrics are available for all Amazon EMR features, but are published at a higher resolution with data at a one-minute granularity when managed scaling is enabled for a cluster. You can correlate the following metrics with the cluster capacity metrics in the previous table to understand the managed scaling decisions.

Metric	Description
AppsCompleted	The number of applications submitted to YARN that have completed. Use case: Monitor cluster progress Units: Count
AppsPending	The number of applications submitted to YARN that are in a pending state. Use case: Monitor cluster progress Units: Count
AppsRunning	The number of applications submitted to YARN that are running. Use case: Monitor cluster progress Units: Count
ContainerAllocated	The number of resource containers allocated by the ResourceManager. Use case: Monitor cluster progress Units: Count
ContainerPending	The number of containers in the queue that have not yet been allocated. Use case: Monitor cluster progress Units: Count
ContainerPendingRatio	The ratio of pending containers to containers allocated (ContainerPendingRatio = ContainerPending / ContainerAllocated). If ContainerAllocated = 0, then ContainerPendingRatio = ContainerPending. The value of ContainerPendingRatio represents a number, not a percentage. This value is useful for scaling cluster resources based on container allocation behavior. Units: Count
HDFSUtilization	The percentage of HDFS storage currently used. Use case: Analyze cluster performance Units: Percent
IsIdle	Indicates that a cluster is no longer performing work, but is still alive and accruing charges. It is set to 1 if no tasks are running and no jobs are running, and set to 0 otherwise. This value is checked at five-minute intervals and a value of 1 indicates only that the cluster was idle when checked, not that it was idle for the entire five minutes. To avoid false positives, you should raise an alarm when this value has been 1 for more than one consecutive five-minute check. For example, you might raise an alarm on this value if it has been 1 for thirty minutes or longer. Use case: Monitor cluster performance Units: Boolean
MemoryAvailableMB	The amount of memory available to be allocated. Use case: Monitor cluster progress Units: Count
MRActiveNodes	The number of nodes presently running MapReduce tasks or jobs. Equivalent to YARN metric mapred.resourcemanager.NoOfActiveNodes. Use case: Monitor cluster progress Units: Count
YARNMemoryAvailablePercentage	The percentage of remaining memory available to YARN (YARNMemoryAvailablePercentage = MemoryAvailableMB / MemoryTotalMB). This value is useful for scaling cluster resources based on YARN memory usage. Units: Percent

Graphing managed scaling metrics

You can graph metrics to visualize your cluster's workload patterns and corresponding scaling decisions made by Amazon EMR managed scaling as the following steps demonstrate.

To graph managed scaling metrics in the CloudWatch console

1. Open the CloudWatch console.

2. In the navigation pane, choose Amazon EMR. You can search on the cluster identifier of the cluster to monitor.

3. Scroll down to the metric to graph. Open a metric to display the graph.

4. To graph one or more metrics, select the check box next to each metric.

The following example illustrates the Amazon EMR managed scaling activity of a cluster. The graph shows three automatic scale-down periods, which save costs when there is a less active workload.

All the cluster capacity and usage metrics are published at one-minute intervals. Additional statistical information is also associated with each one-minute data, which allows you to plot various functions such as Percentiles, Min, Max, Sum, Average, SampleCount.

For example, the following graph plots the same YARNMemoryAvailablePercentage metric at different percentiles, P10, P50, P90, P99, along with Sum, Average, Min, SampleCount.