[Enhancement]: Allow to set preferred_cache_cluster_azs for ElastiCache Redis Сluster

[everythings-gonna-be-alright]

Description

For now, on the AWS web interface, users can choose which available zones they prefer for primary and replica Redis Cluster nodes.
But you can't choose preferred available zones when you create an ElastiCache Redis Cluster as code using Terraform.
As a result, one of the shards is always created in a different zone than your main available zone. This leads to additional traffic transfers and a bad connection time.
Please add the ability to choose preferred_cache_cluster_azs for the Redis Сluster.

Affected Resource(s) and/or Data Source(s)

No response

Potential Terraform Configuration

No response

References

No response

Would you like to implement a fix?

None

[github-actions]

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[acwwat]

Just adding some research notes here.

aws_elasticache_replication_group already has a preferred_cache_cluster_azs argument. This argument is applicable to cluster with cluster mode disabled (per the UI selection).

But perhaps you are referring to the case where cluster mode is enabled. From the CloudTrail event for creating one such cluster, I can see that it doesn't use preferredCacheCluasterAzs but instead use nodeGroupConfiguration:

...
    "requestParameters": {
        "replicationGroupId": "test",
        "replicationGroupDescription": "",
        "automaticFailoverEnabled": true,
        "multiAZEnabled": true,
        "numNodeGroups": 3,
        "replicasPerNodeGroup": 1,
        "nodeGroupConfiguration": [
            {
                "primaryAvailabilityZone": "us-east-1a",
                "replicaAvailabilityZones": [
                    "us-east-1b"
                ]
            },
            {
                "primaryAvailabilityZone": "us-east-1a",
                "replicaAvailabilityZones": [
                    "us-east-1b"
                ]
            },
            {
                "primaryAvailabilityZone": "us-east-1a",
                "replicaAvailabilityZones": [
                    "us-east-1b"
                ]
            }
        ],
...

aws_elasticache_replication_group doesn't seem to support a node_group_configuration block so I think that's what needs to be added to address the requirement.