Redis | Terraform | Creates every time freshly after execution of terraform apply - redis

Question

I am creating Redis in AWS using Terraform. But When I execute terraform apply command for first time it creates without issues. But If I re-run Terraform apply below TF code destroys the Redis and starts re-creating it instead it should tell me that it already exists start focusing on other newly added resources .
Is it expected behaviour of Redis?
Adding terraform plan in the question:
-/+ resource "aws_elasticache_replication_group" "redis" {
apply_immediately = true
at_rest_encryption_enabled = true
auto_minor_version_upgrade = false
automatic_failover_enabled = true
+ configuration_endpoint_address = (known after apply)
engine = "redis"
engine_version = "5.0.4"
~ id = "dev-af-redis" -> (known after apply)
maintenance_window = "sun:06:00-sun:07:00"
~ member_clusters = [
- "ca-cng-dev-af-redis-001",
- "ca-cng-dev-af-redis-002",
] -> (known after apply)
node_type = "cache.t2.medium"
~ number_cache_clusters = 2 -> (known after apply)
parameter_group_name = "default.redis5.0"
port = 6379
~ primary_endpoint_address = "master.dev-af-redis.qxyj8a.euc1.cache.amazonaws.com" -> (known after apply)
replication_group_description = "Airflow Cluster"
replication_group_id = "dev-af-redis"
security_group_ids = [
"sg-094175ad3062da04d",
]
~ security_group_names = [] -> (known after apply)
- snapshot_retention_limit = 0 -> null
~ snapshot_window = "02:30-03:30" -> (known after apply)
subnet_group_name = "dev-subnet-group-airflow"
tags = {
"Application" = "project"
"BusinessUnit" = "subproject"
"Classification" = "private"
"Environment" = "development"
"Name" = "dev-airflow-redis"
"TechnicalOwner" = "ops"
"Tier" = "orchestration"
}
transit_encryption_enabled = true
+ cluster_mode {
+ num_node_groups = 1
+ replicas_per_node_group = 1 # forces replacement
}
}
Plan: 1 to add, 0 to change, 1 to destroy.
TF code which used to create Redis:-
resource "aws_elasticache_replication_group" "cng_redis" {
replication_group_description = "Cluster"
replication_group_id = "dev-af-redis"
engine = "redis"
engine_version = "5.0.4"
node_type = "cache.t2.medium "
port = 6379
subnet_group_name = "dev-subnet-group-airflow"
security_group_ids = ["${aws_security_group.airflow_sg.id}"]
parameter_group_name = "default.redis5.0"
at_rest_encryption_enabled = true
transit_encryption_enabled = true
maintenance_window = "sun:06:00-sun:07:00"
auto_minor_version_upgrade = false
apply_immediately = true
automatic_failover_enabled = true
cluster_mode {
num_node_groups = "1"
replicas_per_node_group = "1"
}
tags = merge(
var.common_tags,
map("Classification", "private"),
map("Name", "airflow-redis")
)
}

Answer 1

Here is a solution ("this is not a bug, it's a feature" case, I suppose ;) ): https://github.com/terraform-providers/terraform-provider-aws/issues/4817#issuecomment-463993424
I tested it and it works.
You have to add parameter group with cluster-enabled set to yes.
I'm using Redis 5.0.5, so to my aws_elasticache_replication_group I added:
resource "aws_elasticache_replication_group" "elc-rep-group" {
...
automatic_failover_enabled = true #this is required, when cluster-enabled parameter is on
parameter_group_name = "default.redis5.0.cluster.on"
...
}