Comment by mediaserf

I generally use hyphens instead of subdomains for SSL certificate purpose and go general-to-specific in the order:

datacenter-application-environment-index.domain.com

example:

ord-web-prod-01.domain.com

For clouds I use the cloud and zone/region:

rs-ord-web-prod-01.domain.com aws-east1-app-stg-01.domain.com