Terraform

TL;DR

# Initialization.
terraform init
terraform init -reconfigure

# Validate files.
terraform validate

# Show 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.
# `destroy` is an alias of `apply -destroy` and is being deprecated.
terraform destroy
terraform apply -destroy

# Format files.
terraform fmt
terraform fmt -check -diff -recursive

# Create a dependency graph.
# Requires `dot` from 'graphviz' for image generation.
terraform graph
terraform graph | dot -Tsvg > graph.svg

# Show an existing 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 modules.
# `get` is being deprecated in favour of `init`
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.

Useful internal variables

Name	Description
`path.root`	filesystem path of the root module of the configuration
`path.module`	filesystem path of the module where the expression is placed
`path.cwd`	filesystem path of the current working directory
`terraform.workspace`	name of the currently selected workspace

Versioning

Troubleshooting

`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"
        }
    }

Sources

for_each vs count

3.9 KiB Raw Blame History