Explanation
You can optionally define multiple configurations for the same provider, and select which one to use on a
per-resource or per-module basis. The primary reason for this is to support multiple regions for a cloud
platform; other examples include targeting multiple Docker hosts, multiple Consul hosts, etc.
To include multiple configurations for a given provider, include multiple provider blocks with the same
provider name, but set the alias meta-argument to an alias name to use for each additional configuration. For
example:
# The default provider configuration
provider "aws" {
region = "us-east-1"
}
# Additional provider configuration for west coast region
provider "aws" {
alias = "west"
region = "us-west-2"
}
https://www.terraform.io/docs/configuration/providers.html