Description

Scale your AWS Elastic MapReduce Cluster by automatically adding or removing Task Instances. Every 5 minutes an AWS Cloudwatch Rule triggers an AWS Lambda Function which checks AWS Cloudwatch Metrics to decide whether to scale up or down.

Scaling Rules

Scaling is only initiated when no scaling is currently in progress. In addition downscaling is not performed during office hours. Apart from that the following rules are used to decide whether to scale or not.

• scaling up
  • at least 1 YARN container has been pending during the past 5 minutes
  • at least 1 task instance group is not running its maximum of configured instances
• scaling down
  • average memory consumption by YARN is below a given threshold for the last hour
  • at least 1 task instance group is running above its minimum of configured instances
  • the current time is not in office hours on a week day

Instance Group Selection

Currently only task instance groups are eligible for scaling and only those with a spot bid price. If the cluster has more than one task instance group it sorts all groups by their bid price in descending order and then selects the first eligible group for scaling.

Build

This project is built using Make. To setup your build environment simply do the following:

make setup-environment

To perform tests, execute

make test

To perform a build, i.e. execute unit tests and package the zip file for AWS Lambda:

make package

If you are getting an error in build due AWS region like this:

autoscaling/venv/lib/python3.9/site-packages/botocore/regions.py", line 148, in _endpoint_for_partition
    raise NoRegionError()
botocore.exceptions.NoRegionError: You must specify a region.

Please, configure a default region for your AWS CLI using the command aws configure and follow the steps. Currently, the default region is eu-west-1.

Deployment to AWS

Committing changes triggers a Jenkins build

Link to the Jenkins build

Parameters

The Function takes 2 sets of parameters:

Mandatory Parameters

• emrJobFlowId
  • ID of the EMR cluster which is to be scaled

Optional Parameters

• emrDownScalingMemoryAllocationThreshold
  • when the average memory consumption by YARN drops below this value a downscaling is triggered
  • floating point in range [0.0, 1.0]
  • defaults to 0.6
• emrScalingMinInstances
  • minimum number of instances that has to be kept for each task instance group
  • integer >= 0
  • defaults to 0
• emrScalingMaxInstances
  • maximum number of instances that is allowed for each task instance group
  • integer >= 0
  • defaults to 20
• officeHoursStart
  • begin of office hour range during which no downscaling will be initiated
  • integer between 0 and 24
  • defaults to 8
• officeHoursEnd
  • end of office hour range during which no downscaling will be initiated
  • integer between 0 and 24
  • defaults to 18