Big Data

Disaster recovery considerations with Amazon EMR on Amazon EC2 for Spark workloads | Amazon Web Services

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Amazon EMR is a cloud big data platform for running large-scale distributed data processing jobs, interactive SQL queries, and machine learning (ML) applications using open-source analytics frameworks such as Apache Spark, Apache Hive, and Presto. Amazon EMR launches all nodes for a given cluster in the same Amazon Elastic Compute Cloud (Amazon EC2) Availability Zone to improve performance. During an Availability Zone failure or due to any unexpected interruption, Amazon EMR may not be accessible, and we need a disaster recovery (DR) strategy to mitigate this problem.

Part of architecting a resilient, highly available Amazon EMR solution is the consideration that failures do occur. These unexpected interruptions can be caused by natural disasters, technical failures, and human interactions resulting in an Availability Zone outage. The EMR cluster could also become unreachable due to failure of critical services running on the EMR master node, network issues, or other issues.

In this post, we show you how to architect your Amazon EMR environment for disaster recovery to maintain business continuity with minimum Recovery Time Objective (RTO) during Availability Zone failure or when your EMR cluster is inoperable.

Although various disaster recovery strategies are available in the cloud, we discuss active-active and active-passive DR strategies for Amazon EMR in this post. We focus on a use case for Spark batch workloads where persistent storage is decoupled from Amazon EMR and the EMR cluster is running with a single master node. If the EMR cluster is used for persistent storage, it requires an additional strategy to replicate data from the EMR cluster, which we will cover in subsequent posts.

Prerequisites

To follow along with this post, you should have a knowledge of Amazon Managed Workflows for Apache Airflow (Amazon MWAA) and an understanding of Network Load Balancers.

Solution overview

The following diagram illustrates the solution architecture.

Customers often use Amazon MWAA to submit Spark jobs to an EMR cluster using an Apache Livy REST interface. We can configure Apache Livy to use a Network Load Balancer hostname instead of an Amazon EMR master hostname, so that we don’t need to update Livy connections from Amazon MWAA whenever a new cluster is created or stopped. You can register Network Load Balancer target groups with multiple EMR cluster master nodes for an active-active setup. In the case of an active-passive setup, we can create a new EMR cluster when a failure is detected and register the new EMR master with the Network Load Balancer target group. The Network Load Balancer automatically performs health checks and distributes requests to healthy targets. With this solution, we can maintain business continuity when an EMR cluster isn’t reachable due to Availability Zone failure or when the cluster is unhealthy due to any other reason.

Active-active DR strategy

An active-active DR setup focuses on running two EMR clusters with identical configuration in two different Availability Zones. To reduce the running costs of two active EMR clusters, we can launch both clusters with minimum capacity, and managed scaling automatically scales the cluster based on the workload. EMR managed scaling only launches instances when there is demand for resources and stops the unneeded instances when the work is finished. With this strategy, we can reduce our recovery time to near zero with optimal cost. This active-active DR strategy is suitable when businesses want to have near-zero downtime with automatic failover for your analytics workloads.

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In the following section, we walk through the steps to implement the solution and provide references to related resources that provide more detailed guidance.

Create EMR clusters

We create two EMR clusters in different Availability Zones within the same Region of your choice. Use the following AWS Command Line Interface (AWS CLI) command and modify or add required configurations as per your needs:

aws emr create-cluster 
  --name "<emr-cluster-az-a>" 
  --release-label emr-6.4.0 
  --log-uri "s3://<your-log-bucket>" 
  --applications Name=Spark Name=Livy 
  --ec2-attributes "KeyName=<your-key-name>,SubnetId=<private-subnet-in-az-a>" 
  --instance-groups InstanceGroupType=MASTER,InstanceCount=1,InstanceType=m4.large InstanceGroupType=CORE,InstanceCount=1,InstanceType=m4.large 
  --use-default-roles

We can create the cluster with EMR managed scaling, which lets you automatically increase or decrease the number of instances or units in your cluster based on workload. Amazon EMR continuously evaluates cluster metrics to make scaling decisions that optimize your clusters for cost and speed.

Create and configure a Network Load Balancer

You can create a Network Load Balancer using the AWS CLI (see Create a Network Load Balancer using the AWS CLI) or the AWS Management Console (see Create a Network Load Balancer). For this post, we do so on the console.

  • Create a target group (emr-livy-dr) and register both EMR clusters’ master IP addresses in the target group.

  • Create an internal Network Load Balancer in the same VPC or Region as your EMR clusters, and choose two different Availability Zones and select the private subnets.
    These subnets don’t need to be in the same subnets as the EMR clusters, but the clusters must allow the traffic from the Network Load Balancer, which is discussed in next steps.

  • Create a TCP listener on port 8998 (the default EMR cluster Livy port) to forward requests to the target group you created.

  • Modify the EMR clusters’ master security groups to allow the Network Load Balancer’s private IP addresses to access port 8998.

You can find the Network Load Balancer’s private IP address by searching the elastic network interfaces for the Network Load Balancer’s name. For access control instructions, refer to How do I attach a security group to my Elastic Load Balancer.

When the target groups become healthy, the Network Load Balancer forwards requests to registered targets when it receives requests on Livy port 8998.

  • Get the DNS name of the Network Load Balancer.

We can also use an Amazon Route 53 alias record to use our own domain name to route traffic to the Network Load Balancer DNS name. We use this DNS name in our Amazon MWAA Livy connection.

Create and configure Amazon MWAA

Complete the following steps:

  • Make sure the execution role you’re using with Amazon MWAA has proper access to EMR clusters and other required services.
  • Update the Amazon MWAA Livy connection (livy_default) host with the Network Load Balancer hostname you created.
  • Create a new Livy connection ID if it’s not already available.

  • Use the following sample DAG to submit a sample Spark application using LivyOperator. We assign the livy_default connection to the livy_conn_id in the DAG code.
  • Enable the DAG and verify if the Spark application is successful on one of the EMR clusters.
from datetime import timedelta, datetime
from airflow.utils.dates import days_ago
from airflow import DAG
from airflow.providers.apache.livy.operators.livy import LivyOperator

default_args = 
    'owner': 'airflow',
    "retries": 1,
    "retry_delay": timedelta(minutes=5),


dag_name = "livy_spark_dag"
# Replace S3 bucket name
# You can use sample spark jar from EMR cluster master node
# /usr/lib/spark/examples/jars/spark-examples.jar
s3_bucket = "artifacts-bucket"
jar_location = "s3:///spark-examples.jar".format(s3_bucket)

dag = DAG(
    dag_id = dag_name,
    default_args=default_args,
    schedule_interval="@once",
    start_date = days_ago(1),
    catchup=False,
    tags=['emr', 'spark', 'livy']
)

livy_spark = LivyOperator(
    file=jar_location,
    class_name="org.apache.spark.examples.SparkPi",
    driver_memory="1g",
    driver_cores=1,
    executor_memory="1g",
    executor_cores=2,
    num_executors=1,
    task_id="livy_spark",
    conf=
    "spark.submit.deployMode": "cluster",
    "spark.app.name": dag_name
    ,
    livy_conn_id="livy_default",
    dag=dag,
)

livy_spark

Test the DR plan

We can test our DR plan by creating scenarios that could be caused by real disasters. Perform the following steps to validate if our DR strategy works automatically during a disaster:

  1. Run the sample DAG multiple times and verify if Spark applications are randomly submitted to the registered EMR clusters.
  2. Stop one of the clusters and verify if jobs are automatically submitted to the other cluster in a different Availability Zone without any issues.
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Active-passive DR strategy

Although the active-active DR strategy has benefits of maintaining near-zero recovery time, it’s complex to maintain two environments because both environments require patching and constant monitoring. In cases where Recovery Time Objective (RTO) and Recovery Point Objective (RPO) aren’t critical for your workloads, we can adopt an active-passive strategy. This approach offers a more economical and operationally less complex approach.

In this approach, we use a single EMR cluster as an active cluster and in case of disaster (due to Availability Zone failures or any other reason the EMR cluster is unhealthy), we launch a second EMR cluster in a different Availability Zone and redirect all our workloads to the newly launched cluster. End-users may notice some delay because launching a second EMR cluster takes time.

The high-level architecture of the active-passive DR solution is shown in the following diagram.

Complete the following steps to implement this solution:

  • Create an EMR cluster in a single Availability Zone.
  • Create target groups and register the EMR cluster master node IP address. Create target group for Resource Manager(8088), Name Node(9870) and Livy(8998) services. Change the port numbers if services are running on different ports.

  • Create a Network Load Balancer and add TCP listeners and forward requests to the respective target groups.

  • Create an Amazon MWAA environment with proper access to the EMR cluster in the same Region.
  • Edit the Amazon MWAA Livy connection to use the Network Load Balancer DNS name.
  • Use the updated Livy connection in Amazon MWAA DAGs to submit Spark applications.
  • Validate if we can successfully submit Spark applications via Livy to the EMR cluster.
  • Set up a DAG on Amazon MWAA or similar scheduling tool that continuously monitors the existing EMR cluster health.
  • Monitor the following key services running on the Amazon EMR master host using REST APIs or commands provided by each service. Add more health checks as required.
  • If the health check process detects a failure of the first EMR cluster, create a new EMR cluster in a different Availability Zone.
  • Automatically register the newly created EMR cluster master IP address to the Network Load Balancer target groups.
  • When the Network Load Balancer health checks are successful with the new EMR cluster master IP, delete the unhealthy EMR cluster master IP address from the target group and stop the old EMR cluster.
  • Validate the DR plan.

Follow the steps mentioned in the active-active DR strategy to create the following resources:

  • Amazon EMR
  • Amazon MWAA
  • Network Load Balancer

The following sample script provides the functionality described in this section. Use this as reference and modify it accordingly to fit your use case.

#!/bin/bash

usage() 
	cat <<EOF
   Usage: ./dr_health_check.sh j-2NPQWXK1U4E6G

   This script takes current EMR cluster id as argument and monitors the cluster health and
   creates new EMR cluster in different AZ if existing cluster is unhealthy/unreachable

EOF
	exit 1


[[ $# -lt 1 ]] && 
	echo Specify cluster id as argument to the script
	usage


#Set NLB DNS name and region
hostname="emr-ap-ae4ffe5g23fd9245.elb.us-west-2.amazonaws.com"
region="us-west-2"
cluster_id=$1
cluster_status=""

export AWS_DEFAULT_REGION=$region

#Depending on the use case perform below health checks for more than one time in a loop and if cluster state is still unhealthy then only perform remaining steps
#Ports and SSL properties for curl command may differ depending on how services are set up
rm_state=$(curl -s --connect-timeout 5 --max-time 10 http://$hostname:8088/ws/v1/cluster | jq -r .clusterInfo.state)
if [[ $? -ne 0 || "$rm_state" != "STARTED" ]]; then
	echo "ResourceManager port not reachable or service not running"
	cluster_status="unhealthy"
fi

nn_state=$(curl -s --connect-timeout 5 --max-time 10 http://$hostname:9870/jmx?qry=Hadoop:service=NameNode,name=NameNodeStatus | jq -r .beans[0].State)
if [[ $? -ne 0 || "$nn_state" != "active" ]]; then
	echo "NameNode port not reachable or service not running"
	cluster_status="unhealthy"
fi

livy_state=$(curl -s --connect-timeout 5 --max-time 10 http://$hostname:8998/sessions)
if [[ $? -ne 0 ]]; then
	echo "Livy port not reachable"
	cluster_status="unhealthy"
fi

cluster_name=$(aws emr describe-cluster --cluster-id $cluster_id | jq -r ".Cluster.Name")

update_target_groups() 
	new_master_ip=$1
	current_master_ip=$2
	current_az=$3

	nlb_arn=$(aws elbv2 describe-load-balancers --query "LoadBalancers[?DNSName==`$hostname`].[LoadBalancerArn]" --output text)
	target_groups=$(aws elbv2 describe-target-groups --load-balancer-arn $nlb_arn --query "TargetGroups[*].TargetGroupArn" --output text)
	IFS=" " read -a tg_array <<<$target_groups
	for tg in "$tg_array[@]"; do
		echo "Registering new EMR master IP with target group $tg"
		aws elbv2 register-targets --target-group-arn $tg --targets Id=$new_master_ip,AvailabilityZone=all

		echo "De-registering old/unhealthy EMR master IP from target group $tg"
		aws elbv2 deregister-targets --target-group-arn $tg --targets Id=$current_master_ip,AvailabilityZone=all
	done


if [[ $cluster_status == "unhealthy" ]]; then
	echo "Cluster status is $cluster_status, creating new EMR cluster"
	current_az=$(aws emr describe-cluster --cluster-id $cluster_id | jq -r ".Cluster.Ec2InstanceAttributes.Ec2AvailabilityZone")
	new_az=$(aws ec2 describe-availability-zones --output json --filters "Name=region-name,Values=$region" --query "AvailabilityZones[?ZoneName!=`$current_az`].ZoneName|[0]" --output=text)
	current_master_ip=$(aws emr list-instances --cluster-id $cluster_id --instance-group-types MASTER --query "Instances[*].PrivateIpAddress" --output text)
	echo "Current/unhealthy cluster id $cluster_id, cluster name $cluster_name,AZ $current_az, Master private ip $current_master_ip"

	echo "Creating new EMR cluster in $new_az"
	emr_op=$(aws emr create-cluster 
		--name "$cluster_name-$new_az" 
		--release-label emr-6.4.0 
		--applications Name=Spark Name=Livy 
		--ec2-attributes "AvailabilityZone=$new_az" 
		--instance-groups InstanceGroupType=MASTER,InstanceCount=1,InstanceType=m4.large InstanceGroupType=CORE,InstanceCount=1,InstanceType=m4.large 
		--use-default-role 
		--region $region)

	new_cluster_id=$(echo $emr_op | jq -r ".ClusterId")

	#wait for cluster provisioning to get master ip address
	sleep 2m

	new_master_ip=$(aws emr list-instances --cluster-id $new_cluster_id --instance-group-types MASTER --query "Instances[*].PrivateIpAddress" --output text)
	echo "New EMR cluster id $new_cluster_id and Master node IP $new_master_ip"

	echo "Terminating unhealthy cluster $cluster_id/$cluster_name in $current_az"
	aws emr modify-cluster-attributes --cluster-id $cluster_id --no-termination-protected
	aws emr terminate-clusters --cluster-ids $cluster_id

	echo "Register new EMR master IP address with NLB target groups and de-register unhealthy EMR master"
	update_target_groups $new_master_ip $current_master_ip $current_az
else
	echo "Current cluster $cluster_id/$cluster_name is healthy"
fi

Summary

In this post, we shared some solutions and considerations to improve DR implementation using Amazon EMR on Amazon EC2, Network Load Balancer, and Amazon MWAA. Based on your use case, you can determine the type of DR strategy you want to deploy. We have provided the steps required to create the necessary environments and set up a successful DR strategy.

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For more details about the systems and processes described in this post, refer to the following:


About the Author

Bharat Gamini is a Data Architect focused on Big Data & Analytics at Amazon Web Services. He helps customers architect and build highly scalable, robust and secure cloud-based analytical solutions on AWS.

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