Creating custom parameter group in AWS Elasticache based on default groups

Question

I am trying to create custom parameter group in AWS Elasticache.

I'd like to use a default parameter group as a base (group named default.redis5.0.cluster.on, as there is everything else I need but just one property I'd like to change), see https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/ParameterGroups.Redis.html for more details about default parameter groups

My basic assumption would be that I'd need to copy the default parameter group values to a Terraform resource and then just modify the only parameter I need to change. However, this would produce huge list of parameters and wouldn't seem the simplest way to do this.

If I need to do copy parameters in the default.redis5.0.cluster.on parameter group, then I'd need to have those in Terraform. Is there a way to import a default resource group as Terraform configuration?

Answer 1

It's possible to create parameter group with family = redis5.0 that has got almost identical parameters with the default parameter group default.redis5.0.cluster.on.

I ended up doing JSON diff for the properties in the two parameter groups: default.redis5.0and default.redis5.0.cluster.onand there was just one parameter difference. First, get the parameter groups as JSON:

aws elasticache describe-cache-parameters --cache-parameter-group-name default.redis5.0.cluster.on > default.redis5.0.cluster.on.json
aws elasticache describe-cache-parameters --cache-parameter-group-name default.redis5.0 > default.redis5.0.json

Then do a JSON diff for the two files to obtain parameters that are different. There was only one, cluster-enabled so after that it was trivial to do a custom resource group that had same parameter values as default.redis5.0.cluster.on this way:

resource "aws_elasticache_parameter_group" "aws_elasticache_parameter_group" {
  name        = "cache-params"
  family      = "redis5.0"
  description = "The parameter group has same values as default parameter group default.redis5.0.cluster.on"

  parameter {
    name  = "cluster-enabled"
    value = "yes"
  }
}