How readiness checks, resource sets, and readiness scopes work together - Amazon Route 53 Application Recovery Controller
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How readiness checks, resource sets, and readiness scopes work together

Readiness checks always audit groups of resources in resource sets. You create resource sets (separately, or while you're creating a readiness check) to group the resources that are in the cells (Availability Zones or Amazon Regions) in your Route 53 ARC recovery group, so that you can define readiness checks. A resource set is typically a group of same type of resources (like Network Load Balancers) but can also be DNS target resources, for architectural readiness checks.

You typically create one resource set and readiness check for each type of resource in your application. For an architectural readiness check, you create a top level DNS target resource and a global (recovery group level) resource set for it, and then create cell level DNS target resources, for a separate resource set.

The following diagram shows an example of a recovery group with three cells (Availability Zones), each with a Network Load Balancer (NLB) and Auto Scaling group (ASG).

A sample recovery group for Route 53 ARC. It has three cells (AZs), each with one NLB and one EC2 Auto Scaling group.

In this scenario, you would create a resource set and readiness check for the three Network Load Balancers, and a resource set and readiness check for the three Auto Scaling groups. Now you have a readiness check for each set of resources for your recovery group, by resource type.

By creating readiness scopes for resources, you can add readiness check summaries for cells or recovery groups. To specify a readiness scope for a resource, you associate the ARN of the cell or recovery group with each resource in a resource set. You can do this when you're creating a readiness check for a resource set.

For example, when you add a readiness check for a resource set for the Network Load Balancers for this recovery group, you can add readiness scopes to each NLB at the same time. In this case, you would associate the ARN of AZ 1a to the NLB in AZ 1a, the ARN of AZ 1b to the NLB AZ 1b, and the ARN of AZ 1c to the NLB in AZ 1c. When you create a readiness check for the Auto Scaling groups, you would do the same, assigning readiness scopes to each of them when you create the readiness check for the Auto Scaling group resource set.

It’s optional to associate readiness scopes when you create a readiness check, however, we strongly recommend that you set them. Readiness scopes enable Route 53 ARC to show the correct READY or NOT READY readiness status for recovery group summary readiness checks and cell level summary readiness checks. Unless you set readiness scopes, Route 53 ARC can't provide these summaries.

Note that when you add an application-level or a global resource, such as a DNS routing policy, you don't choose a recovery group or cell for the readiness scope. Instead, you choose global resource (no cell).