Metadata

Id: terraform-aws-elasticache-nodes-not-created-across-multi-az

Provider: AWS

Platform: Terraform

Severity: Medium

Category: Availability

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Description

When configuring AWS ElastiCache clusters with multiple nodes, it is important to distribute nodes across multiple Availability Zones (AZs) by setting the az_mode attribute to "cross-az". Failing to do so—such as by omitting the az_mode attribute or explicitly setting it to "single-az"—means all nodes run in a single AZ, increasing the risk of service disruption if that AZ experiences an outage. For example, a secure Terraform configuration explicitly sets the following:

resource "aws_elasticache_cluster" "example" {
  cluster_id    = "cluster-example"
  engine        = "memcached"
  num_cache_nodes = 3
  az_mode       = "cross-az"
}

Distributing cache nodes across multiple AZs increases fault tolerance and availability for ElastiCache clusters.

Compliant Code Examples

resource "aws_elasticache_cluster" "negative1" {
  cluster_id           = "cluster-example"
  engine = "memcached"

  num_cache_nodes = 3

  az_mode = "cross-az"
}

Non-Compliant Code Examples

resource "aws_elasticache_cluster" "positive1" {
  cluster_id = "cluster-example"
  engine = "memcached"
  num_cache_nodes = 3
}

resource "aws_elasticache_cluster" "positive2" {
  cluster_id = "cluster-example"
  engine = "memcached"
  num_cache_nodes = 3

  az_mode = "single-az"
}