Cyclic dependency terraform

Question

I have a cyclic dependency problem with terraform. I have a user pool user_pool which invokes a lambda user_signup_lambda as a trigger when a user signs up. This lambda also needs the user pool's Id as an environment variable.

My terraform looks like this

resource "aws_lambda_function" "user_signup_lambda" {
  function_name = "user_signup_lambda"
  filename = var.file_name
  source_code_hash = filebase64sha256(var.file_name)
  handler = var.handler
  runtime = var.runtime
  memory_size = var.memory_size
  timeout = var.timeout
  role = var.iam_role_arn

  environment {
    variables = aws_cognito_user_pool.user_pool.id
  }
}

resource "aws_cognito_user_pool" "user_pool" {
  name = "some-user-pool"

  ....other config

  lambda_config {
     post_confirmation = module.user_signup_lambda.arn
  }

This results in the following error:

Error: Cycle: module.user_signup_lambda.var.environment_variables, module.user_signup_lambda.aws_lambda_function.lambda_function, module.user_signup_lambda.output.arn, aws_cognito_user_pool.user_pool

Is there anyway around this other than hardcoding the user pool id?

user_1667822 · Answer

We had the exact same issue. We ended up passing a variable containing the UserPool Name to Both UserPool and Lambda trigger resources.

The lambda then fetches the Cognito user pool info from it's name.

This way there is no cycle dependency between those 2 resources.

# Module containing Cognito userPool
resource "aws_cognito_user_pool" "default" {

 ...
  # Triggers
  lambda_config {
    post_confirmation = module.cognito_post_confirmation.lambda_post_confirmation.arn
  }
  name = var.cognito_identity_pool_name
} 


module "cognito_post_confirmation" {
  source                     = "./triggers/post-confirmation"
  cognito_identity_pool_name = var.cognito_identity_pool_name
  ...
}

Cyclic dependency terraform

1 Answers