Readiness check components

A cell defines your application's replicas or independent units of failover. It groups all the Amazon resources that are necessary for your application to run independently within the replica. For example, you might have one set of resources in a primary cell and another set in a standby cell. You determine the boundary of what a cell includes, but cells typically represent an Availability Zone or a Region. You can have multiple cells (nested cells) within a cell, such as AZs within a Region. Each nested cell represents an isolated unit of failover.

Cells are collected into a recovery group. A recovery group represents an application or group of applications that you want to check failover readiness for. It consists of two or more cells, or replicas, that match each other in terms of functionality. For example, if you have a web application that is replicated across us-east-1a and us-east-1b, where us-east-1b is your failover environment, you can represent this application in ARC as a recovery group with two cells: one in us-east-1a and one in us-east-1b. A recovery group can also include a global resource, such as a Route 53 health check.

When you create components for readiness checks in ARC, you specify a resource, such as an Amazon DynamoDB table, a Network Load Balancer, or a DNS target resource, by using a resource identifier. A resource identifier is either the Amazon Resource Name (ARN) for the resource or, for a DNS target resource, the identifier that ARC generates when it creates the resource.

A DNS target resource is the combination of your application's domain name and other DNS information, such as the Amazon resource that the domain points to. Including an Amazon resource is optional but if you provide it, it must be a Route 53 resource record or a Network Load Balancer. When you provide the Amazon resource, you can get more detailed architectural recommendations that can help you improve your application's recovery resiliency. You can create resource sets in ARC for DNS target resources, and then create a readiness check for the resource set so that you can get architecture recommendations for your application. The readiness check also monitors the DNS routing policy for your application, based on the readiness rules for DNS target resources.

A resource set is a set of resources, including Amazon resources or DNS target resources, that span multiple cells. For example, you might have a load balancer in us-east-1a and another one in us-east-1b. To monitor the recovery readiness of the load balancers, you can create a resource set that includes both load balancers, and then create a readiness check for the resource set. ARC will continually check the readiness of the resources in the set. You can also add a readiness scope to associate resources in a resource set with the recovery group that you create for your application.

Readiness rules are audits that ARC performs against a set of resources in a resource set. ARC has a set of readiness rules for each type of resource that it supports readiness checks for. Each rule includes an ID and a description that explains what ARC inspects the resources for.

A readiness check monitors a resource set in your application, such as a set of Amazon Aurora instances, that ARC is auditing recovery readiness for. Readiness checks can include auditing, for example, capacity configurations, Amazon quotas, or routing policies. For example, if you want to audit readiness for your Amazon EC2 Auto Scaling groups across two Availability Zones, you can create a readiness check for a resource set with two resource ARNs, one for each Auto Scaling group. Then, to make sure that each group is scaled equally, ARC continually monitors the instance types and the counts in the two groups.

A readiness scope identifies the grouping of resources that a specific readiness check encompasses. The scope of a readiness check can be a recovery group (that is, global to the whole application) or a cell (that is, a Region or Availability Zone). For a resource that is a global resource for ARC, set the readiness scope at to recovery group or global resource level. For example, a Route 53 health check is a global resource in ARC because it isn't specific to a Region or Availability Zone.