This error occurs when a Terraform resource or module is missing a mandatory argument that the provider or module definition requires. Terraform will tell you exactly which argument is missing and which resource it applies to.
Terraform has detected that a resource block or module call is missing a required argument. Required arguments are inputs that must be provided—they have no default values. This commonly happens when: 1. You're using a resource type and haven't provided all the arguments the provider expects 2. You're calling a module but haven't supplied required input variables 3. You've updated a provider version where previously optional arguments became required 4. You have a typo in the argument name, so Terraform thinks it's missing The error message will specify which argument is missing and the line number where the problem occurs.
The error output will tell you:
- The exact argument name that's missing
- The resource or module type
- The file and line number
Example:
Error: Missing required argument
on main.tf line 5, in resource "aws_instance" "example":
5: resource "aws_instance" "example" {
The argument "ami" is required, but no definition was found.Look up the resource or module you're using in the official documentation:
1. For built-in resources: Visit the Terraform provider documentation (e.g., terraform.io/docs/providers/aws/r/instance)
2. For modules: Check the module's README or source repository
3. Look at the 'Required' or 'Arguments' section
Note the required arguments and their expected types and formats.
Add the missing argument to the resource or module block. Make sure you use the correct argument name and provide a valid value.
Example for a missing ami argument:
resource "aws_instance" "example" {
ami = "ami-12345678" # Add this
instance_type = "t2.micro"
}For module inputs:
module "vpc" {
source = "./modules/vpc"
cidr = "10.0.0.0/16" # Add this
region = "us-east-1"
}Run terraform validate to check your configuration syntax and required arguments:
terraform validateThis will catch missing required arguments without applying changes. Fix any errors and re-run validate until it passes.
If you recently upgraded a provider, some arguments may have become required:
# Check current provider versions
terraform version
# Update to latest provider versions
terraform init -upgradeAfter upgrading, run terraform validate again to see if new required arguments are needed.
Required vs Optional Arguments: In Terraform, arguments are required if they have no default value in the resource definition. Arguments with default values are optional. When you define your own modules, you can control which variables are required by including or omitting default values in the variable block.
For nested blocks (like ingress in security groups), if the block itself is required, you must include at least one instance of it even if all its arguments have defaults.
Use the -json flag with terraform validate for machine-readable error output: terraform validate -json
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