Terraform "Invalid value for variable" - Custom Validation Failed in CI

An input value did not satisfy a variable’s declared type or a custom validation block. Terraform stops because the value is outside what the configuration allows.

What this error means

plan/apply fails with "Invalid value for variable" and the custom error message from the validation block, or a type error. It surfaces when CI passes a tfvar/env value that breaks the variable’s constraints.

terraform output

Error: Invalid value for variable

  on variables.tf line 5:
   5: variable "environment" {

The "environment" value must be one of: dev, staging, prod.

This was checked by the validation rule at variables.tf:8,3-13.

Common causes

Value fails a custom validation rule

A validation block’s condition returned false for the supplied value, so Terraform rejects it with the block’s error_message.

Value is the wrong type

Passing a string where a number/bool/list is declared (common with env-var inputs that arrive as strings) fails the variable’s type constraint.

How to fix it

Supply a value that satisfies the rule

Read the validation message and pass an allowed value; for typed inputs, pass the correct type.

variables.tf

# the validation that rejected the input
variable "environment" {
  type = string
  validation {
    condition     = contains(["dev","staging","prod"], var.environment)
    error_message = "The environment value must be one of: dev, staging, prod."
  }
}

Pass correctly-typed values from CI

Confirm the tfvar/env value matches the variable’s declared type.
For numbers/bools coming from env vars, ensure they are not quoted strings where a primitive is expected.
Re-run with a value the validation allows.

How to prevent it

Document allowed values in error_message so CI failures are self-explanatory.
Validate tfvars against the variable types before applying.
Keep CI-provided inputs within the declared constraints.