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

[ghost]

This issue was originally opened by @alepeltier as hashicorp/terraform#23044. It was migrated here as a result of the provider split. The original body of the issue is below.

---

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

[pauliuspetka]

I think You can solve this by adding cluster_mode to condition:

`    dynamic "cluster_mode" {
        for_each = "${var.cacheClusterMode == 0 ? [] : var.eCaches}"
         content { 
                 replicas_per_node_group = "${cluster_mode.value.replicas_per_node_group}"
                 num_node_groups         = "${cluster_mode.value.num_node_groups}"
         }
        }`

[alepeltier]

@pauliuspetka

Thanks for your reply. I'm struggling to see how a dynamic block will help in this situation though. The cluster block always has populated variables and I always want it to be enabled. Dynamic blocks are usually used if you want to dynamically render some code which I'm not particularly interested in doing.

For me, if cluster_mode {} is set the code should automatically create a clustered instance. Have I missed something here I'd be interested in hearing how you go round this issue?

[syntastical]

The ElastiCache Terraform is very confusing and in my opinion needs to be revamped and updated. However, you should either specify number_cache_clusters or cluster_mode, not both. The official documentation states the follow "number_cache_clusters - (Required for Cluster Mode Disabled) ".

[gdavison]

As mentioned above, only one of cluster_mode or number_cache_clusters. More recent versions give a better error message.

We have also opened #14959 to address the design of the ElastiCache resources

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!