3.2 KiB
Terraform
TL;DR
# init
terraform init
terraform init -reconfigure
# check what would be done
terraform plan
terraform plan -out path/to/file.tfstate -parallelism 50
# make the changes
terraform apply
terraform apply -auto-approve -backup -parallelism 25 path/to/plan.tfstate
# destroy everything
terraform destroy
# check files formatting
terraform fmt
terraform fmt -check -diff -recursive
# validate files
terraform validate
# create a graph
# requires dot from graphviz for image generation
terraform graph
terraform graph | dot -Tsvg > graph.svg
# show a created resource
terraform state show 'packet_device.worker'
terraform state show 'packet_device.worker["example"]'
terraform state show 'module.foo.packet_device.worker'
# recursively update all needed modules
terraform get -update -no-color
Modules
Include a module in the configuration with the module keyword:
module "remote_vpc_module" {
# module settings
source = "terraform-aws-modules/vpc/aws" # required
version = "2.21.0"
# module variables
…
}
module "local_vpc_module" {
# module settings
source = "./modules/aws_vpc" # required
# module variables
…
}
Run terraform init or terraform get to install the modules.
Modules are installed in the .terraform/modules directory inside the configuration's working directory; local modules are symlinked from there.
When terraform processes a module block, that block will inherit the provider from the enclosing configuration.
A module's output can be accessed from the configuration that calls the module through the syntax module.$moduleName.$outputName. Module outputs are read-only attributes.
Gotchas
count vs for_each
count creates an unordered list of objects, while for_each creates a map.
count is sensitive to any changes in the list order and this means that if for some reason order of the list is changed terraform will force the replacement of all resources for which the index in the list has changed:
variable "my_list" {
- default = ["first", "second", "third"]
+ default = ["zeroth", "first", "second", "third"]
}
Terraform will perform the following actions:
# null_resource.default[0] must be replaced
-/+ resource "null_resource" "default" {
~ id = "4074861383382414527" -> (known after apply)
~ triggers = { # forces replacement
"list_index" = "0"
~ "list_value" = "first" -> "zeroth"
}
}
…
# null_resource.default[3] will be created
+ resource "null_resource" "default" {
+ id = (known after apply)
+ triggers = {
+ "list_index" = "3"
+ "list_value" = "third"
}
}