Terraform CLI Tutorials Flashcards
(44 cards)
Terraform Variables vs Conventional Programming Language Variables
Terraform’s input variables don’t change values during a Terraform run such as plan, apply, or destroy.
Instead, they allow users to more safely customize their infrastructure by assigning different values to the variables before execution begins.
Terraform Variables can be defined where…
Anywhere in a configuration file (not recommended)
In separate variables.tf file (recommended)
A Variable Blocks three optional args
Description: A short description to document the purpose of the variable.
Type: The type of data contained in the variable.
Default: The default value.
e.g.,
variable "aws_region" {
description = "AWS region"
type = string
default = "us-west-2"
}
Referencing a variable in Terraform configuration file
var. variable_name
e. g.,
provider “aws” {
region = var.aws_region
}
Terraform simple variable types
string, int, bool
Terraform collection variable types
List: A sequence of values of the same type.
Map: A lookup table, matching keys to values, all of the same type.
Set: An unordered collection of unique values, all of the same type.
Defining a List Type variable
e.g.,
variable "public_subnet_cidr_blocks" {
description = "Available cidr blocks for public subnets."
type = list(string)
default = [
"10.0.1.0/24",
"10.0.2.0/24",
"10.0.3.0/24",
"10.0.4.0/24",
"10.0.5.0/24",
"10.0.6.0/24",
"10.0.7.0/24",
"10.0.8.0/24",
]
}
Accessing multiple items in a list
slice() function
slice(list_object, start_index, end_index)
[‘a’, ‘b’] = slice([‘a’, ‘b’, ‘c’, ‘d’], 0, 2)
Defining a Map Type variable
map(Type)
e.g. map(string) -> a map of strings. Keys are always strings.
Note: A map is like a python dict
You will be prompted to assign a value to variable if…
there is no default value defined
Variable string interpolation
“The value of the variable is ${var.var_name}”
Variable string interpolation
“The value of the variable is ${var.var_name}”
Variable validation
Use a validation block within the variable block to perform validation on the values provided for a variable.
Validation block contains a condition and an error message (string)
variable "example"{
...
...
validation{
condition = length(var.example) < 10
error_message = "Example is too long"
}
}
terraform init
Command to initialize your terraform configuration.
Terraform lock file
.terraform.lock.hcl
A file that records the versions and hashes of the providers used in this run. It ensures consistent Terraform runs in different environments.
.terraform directory
an artifact of terraform init
Stores the providers and modules defined in the project.
terraform plan
provides a preview of the actions Terraform would take to modify your infrastructure.
Plan ( .configuration object )
is a snapshot of your configuration at the time of the terraform plan.
This configuration snapshot captures the versions of the providers recorded in your .terraform.lock.hcl
Plan ( .resource_changes object )
action field= action taken for this resource
before field=resource state prior to this run
after field=state to define for the resource
after_unknown field=the list of values that will be computed or determined through the operation
before_sensitive and after_sensitive fields = list of any values marked sensitive
Plan ( .planned_values object)
another view of the differences between the “before” and “after” values of your resources, showing you the planned outcome for a run that would use this plan file.
Steps taken by Terraform when running terraform apply
- Lock the Projects State.
- ______
- ______
- ______
- ______
- Print out report of the changes made
1 Lock Projects state 2 Create a plan (same as terraform plan) and prompt your approval 3 Execute the steps defined in the plan 4 Update state file 5 Unlock the state file 6 Print out report of the changes made
What does Terraform do when there are errors during terraform apply (4 events)
1 Errors are logged and reported to the console
2 Updates the state file with any changes to resources
3 Unlocks the state file
4 Exits
State of infrastructure after a partially completed apply step (i.e. errors during terraform apply)
Infrastructure may be in an invalid state.
You must resolve the error then apply the config again to update your infrastructure to the desired state
terraform apply -replace
when a resource has become unhealthy or stops working in ways that are outside of Terraform’s control.
You want to instruct Terraform to reprovision the resource using the same configuration.
The -replace argument requires a resource address. List the resources in your configuration with terraform state list.
