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Auto Scaling ElastiCache (Redis OSS) clusters

Prerequisites

ElastiCache (Redis OSS) Auto Scaling is limited to the following:

Managing Capacity Automatically with ElastiCache (Redis OSS) Auto Scaling

ElastiCache (Redis OSS) auto scaling is the ability to increase or decrease the desired shards or replicas in your ElastiCache (Redis OSS) service automatically. ElastiCache (Redis OSS) leverages the Application Auto Scaling service to provide this functionality. For more information, see Application Auto Scaling. To use automatic scaling, you define and apply a scaling policy that uses CloudWatch metrics and target values that you assign. ElastiCache (Redis OSS) auto scaling uses the policy to increase or decrease the number of instances in response to actual workloads.

You can use the Amazon Web Services Management Console to apply a scaling policy based on a predefined metric. A predefined metric is defined in an enumeration so that you can specify it by name in code or use it in the Amazon Web Services Management Console. Custom metrics are not available for selection using the Amazon Web Services Management Console. Alternatively, you can use either the Amazon CLI or the Application Auto Scaling API to apply a scaling policy based on a predefined or custom metric.

ElastiCache (Redis OSS) supports scaling for the following dimensions:

ElastiCache (Redis OSS) supports the following types of automatic scaling policies:

The following steps summarize the ElastiCache (Redis OSS) auto scaling process as shown in the previous diagram:

To understand how ElastiCache (Redis OSS) Auto Scaling works, suppose that you have a cluster named UsersCluster. By monitoring the CloudWatch metrics for UsersCluster, you determine the Max shards that the cluster requires when traffic is at its peak and Min Shards when traffic is at its lowest point. You also decide a target value for CPU utilization for the UsersCluster cluster. ElastiCache (Redis OSS) auto scaling uses its target tracking algorithm to ensure that the provisioned shards of UsersCluster is adjusted as required so that utilization remains at or near to the target value.

IAM Permissions Required for ElastiCache (Redis OSS) Auto Scaling

ElastiCache (Redis OSS) Auto Scaling is made possible by a combination of the ElastiCache (Redis OSS), CloudWatch, and Application Auto Scaling APIs. Clusters are created and updated with ElastiCache (Redis OSS), alarms are created with CloudWatch, and scaling policies are created with Application Auto Scaling. In addition to the standard IAM permissions for creating and updating clusters, the IAM user that accesses ElastiCache (Redis OSS) Auto Scaling settings must have the appropriate permissions for the services that support dynamic scaling. IAM users must have permissions to use the actions shown in the following example policy:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "application-autoscaling:*",
                "elasticache:DescribeReplicationGroups",
                "elasticache:ModifyReplicationGroupShardConfiguration",
                "elasticache:IncreaseReplicaCount",
                "elasticache:DecreaseReplicaCount",
                "elasticache:DescribeCacheClusters",
                "elasticache:DescribeCacheParameters",
                "cloudwatch:DeleteAlarms",
                "cloudwatch:DescribeAlarmHistory",
                "cloudwatch:DescribeAlarms",
                "cloudwatch:DescribeAlarmsForMetric",
                "cloudwatch:GetMetricStatistics",
                "cloudwatch:ListMetrics",
                "cloudwatch:PutMetricAlarm",
                "cloudwatch:DisableAlarmActions",
                "cloudwatch:EnableAlarmActions",
                "iam:CreateServiceLinkedRole",
                "sns:CreateTopic",
                "sns:Subscribe",
                "sns:Get*",
                "sns:List*"
            ],
            "Resource": "arn:aws:iam::123456789012:role/autoscaling-roles-for-cluster"
        }
    ]
}

Service-linked role

The ElastiCache (Redis OSS) auto scaling service also needs permission to describe your clusters and CloudWatch alarms, and permissions to modify your ElastiCache (Redis OSS) target capacity on your behalf. If you enable Auto Scaling for your ElastiCache (Redis OSS) cluster, it creates a service-linked role named AWSServiceRoleForApplicationAutoScaling_ElastiCacheRG. This service-linked role grants ElastiCache (Redis OSS) auto scaling permission to describe the alarms for your policies, to monitor the current capacity of the fleet, and to modify the capacity of the fleet. The service-linked role is the default role for ElastiCache (Redis OSS) auto scaling. For more information, see Service-linked roles for ElastiCache (Redis OSS) auto scaling in the Application Auto Scaling User Guide.

Auto Scaling Best Practices

Before registering to Auto Scaling, we recommend the following:

After registering to AutoScaling, note the following: