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Auto Scaling ElastiCache for Redis clusters

Prerequisites

ElastiCache for Redis Auto Scaling is limited to the following:

Managing Capacity Automatically with ElastiCache for Redis Auto Scaling

ElastiCache for Redis auto scaling is the ability to increase or decrease the desired shards or replicas in your ElastiCache for Redis service automatically. ElastiCache for Redis 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 for Redis 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 for Redis supports scaling for the following dimensions:

ElastiCache for Redis supports the following types of automatic scaling policies:

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

To understand how ElastiCache for Redis 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 for Redis 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 for Redis Auto Scaling

ElastiCache for Redis Auto Scaling is made possible by a combination of the ElastiCache for Redis, CloudWatch, and Application Auto Scaling APIs. Clusters are created and updated with ElastiCache for Redis, 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 for Redis 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 for Redis auto scaling service also needs permission to describe your clusters and CloudWatch alarms, and permissions to modify your ElastiCache for Redis target capacity on your behalf. If you enable Auto Scaling for your ElastiCache for Redis cluster, it creates a service-linked role named AWSServiceRoleForApplicationAutoScaling_ElastiCacheRG. This service-linked role grants ElastiCache for Redis 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 for Redis auto scaling. For more information, see Service-linked roles for ElastiCache for Redis 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: