Explanation
Version
When using modules installed from a module registry, we recommend explicitly constraining the acceptable
version numbers to avoid unexpected or unwanted changes.
Use the version argument in the module block to specify versions:
module "consul" {
source = "hashicorp/consul/aws"
version = "0.0.5"
servers = 3
}
Reference: https://www.terraform.io/docs/language/modules/sources.html

Explanation
https://www.phillipsj.net/posts/introduction-to-terraform-provisioners/
As you continue learning about Terraform, you will start hearing about provisioners. Terraform provisioners
can be created on any resource and provide a way to execute actions on local or remote machines.
https://www.terraform.io/language/resources/provisioners/local-exec

Explanation
"The terraform plan command creates an execution plan, which lets you preview the changes that Terraform
plans to make to your infrastructure. By default, when Terraform creates a plan it:
Reads the current state of any already-existing remote objects to make sure that the Terraform state is
up-to-date.
Compares the current configuration to the prior state and noting any differences.
Proposes a set of change actions that should, if applied, make the remote objects match the configuration."
"The plan command alone will not actually carry out the proposed changes, and so you can use this command
to check whether the proposed changes match what you expected before you apply the changes or share your
changes with your team for broader review.
If Terraform detects that no changes are needed to resource instances or to root module output values,
terraform plan will report that no actions need to be taken."
https://www.terraform.io/cli/commands/plan