Error: Either number_cache_clusters or cluster_mode must be set when both are

[alepeltier]

Terraform Version

Terraform v0.12.10

Terraform Configuration Files

resource "aws_elasticache_replication_group" "shared_microservice_cache" {
  engine                = "redis"
  node_type             = var.elasticache_instance_type
  port                  = 6379
 number_cache_clusters = 3

  // Time is in UTC
  maintenance_window = "sun:03:00-sun:06:00"

  snapshot_retention_limit = var.elasticache_snapshot_rentention_limit
  snapshot_window          = "00:00-02:00"

  subnet_group_name  = aws_elasticache_subnet_group.default.name
  security_group_ids = [module.security_group.id]

  automatic_failover_enabled = true

  replication_group_description = format("%s %s %s",
    "A redis cache which can be used by any microservice in the",
    var.environment,
    "environment"
  )

  replication_group_id = format("%s-%s",
    "microservice",
    var.environment
  )

  at_rest_encryption_enabled = true
  transit_encryption_enabled = true
  auth_token                 = random_password.redis_password.result

  cluster_mode {
    replicas_per_node_group = var.elasticache_replicas_per_node_group
    num_node_groups         = var.elasticache_num_node_groups
  }
}

Expected Behavior

According to the documentation, I should be able to make a clustered Redis cache by setting either cluster_mode or number_cache_clusters. I have both set in the above code however when I run an apply Terraform throws an error saying I need to have them set. I've had this issue multiple times and don't think it is the expected behaviour unless I'm doing something wrong.

Actual Behavior

I get the following error

Error: Either `number_cache_clusters` or `cluster_mode` must be set

  on main.tf line 82, in resource "aws_elasticache_replication_group" "shared_microservice_cache":
  82: resource "aws_elasticache_replication_group" "shared_microservice_cache" {

Steps to Reproduce

1: Run terraform apply

[ghost]

This issue has been automatically migrated to hashicorp/terraform-provider-aws#10458 because it looks like an issue with that provider. If you believe this is not an issue with the provider, please reply to hashicorp/terraform-provider-aws#10458.

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