What goes missing when a cloud region goes down

What does a region hold besides servers?

A running application in one cloud region depends on far more than its virtual machines and databases. It sits in a virtual network with subnets and route tables. Security groups and network ACLs decide what can talk to what. IAM roles and instance profiles let services call each other. DNS records point users at load balancers in that region. Certificates, secrets, queues, Kubernetes clusters and dozens of service settings complete the picture.

A data backup copies the contents of disks, databases and buckets. It does not, by itself, recreate the network, the identity bindings or the DNS that make the data reachable.

What does AWS say you need in the recovery region?

The AWS whitepaper on disaster recovery options in the cloud is direct about it: to recover in another region "you must redeploy the infrastructure, configuration, and application code in the recovery Region". It describes four strategies, from backup and restore to multi-site active/active, that differ mainly in how much of that environment is already running before the incident. The same whitepaper recommends infrastructure as code so the environment can be redeployed consistently.

Which parts are usually missing?

Teams that rehearse a region loss tend to find the same gaps:

• Resources created by hand in the console, which no template describes.
• Identity: roles and policies that exist only in the primary account or region.
• DNS and certificates that point at, or were issued for, the primary region's endpoints.
• Service settings that drifted from the template after it was first applied.

Each of these is cheap to fix before an incident and slow to fix during one.

How do the tools here approach it?

The tools scored on this site approach the problem differently. Firefly documents capturing configuration, networking, identity and DNS and rebuilding them as Terraform in another region or account; its coverage table lists 190 AWS and 86 Azure resource types. Arpio replicates infrastructure and data continuously and fails over across regions and accounts on AWS and across subscriptions on Azure. The rankings score how fully each tool documents this, under rebuild scope and region and account loss.

How does a region loss differ from an account loss?

A region loss leaves your accounts, identities and other regions intact; the job is to stand the environment up somewhere else. An account loss, for example after an attacker takes control of it or deletes its resources, can remove the identity layer as well, and the recovery target must be a different, clean account. Plans that cover only the first case often assume access that the second case removes. Our criterion for this is called region and account loss for that reason.

What should you take from this lesson?

Write down what your application needs in a second region, layer by layer, before you choose a tool. Then ask each vendor which of those layers it brings back, and in what form.