Description
Placing Memcached nodes in one Availability Zone can leave all of them affected by a zone failure, even with multiple nodes. Use az_mode = "cross-az" to distribute nodes across zones.
Potential impact
A zone failure affecting several cache nodes can reduce cache hit rates and service performance. Distributing nodes across zones does not replicate Memcached data.
Remediation
Set az_mode = "cross-az" for Memcached clusters with at least two nodes. Check that the subnet group and node placement support multiple Availability Zones.
Examples
The examples show only the Memcached node count and Availability Zone settings. Other required settings, such as node type, are omitted.
Before
hcl
resource "aws_elasticache_cluster" "example" {
cluster_id = "cluster-example"
engine = "memcached"
num_cache_nodes = 3
}
After
hcl
resource "aws_elasticache_cluster" "example" {
cluster_id = "cluster-example"
engine = "memcached"
num_cache_nodes = 3
az_mode = "cross-az"
}