Elasticsearch domains should have at least three data nodes

How to fix it

• Interrupts service: Spreading the domain across more Availability Zones runs a blue/green deployment, so latency and rejected requests can rise while data copies; adding nodes alone does not.

In the console

OpenSearch Service → Domains → the domain → Actions → Edit cluster configuration

Number of nodes

3 or more, a multiple of the Availability Zone count so each zone holds the same number

Availability Zones

3-AZ where the Region has three; a VPC domain needs a subnet in each zone

With the AWS CLI

aws es update-elasticsearch-domain-config --domain-name <domain-name> --elasticsearch-cluster-config '{"InstanceCount":3,"ZoneAwarenessEnabled":true,"ZoneAwarenessConfig":{"AvailabilityZoneCount":3}}' --region <region>

With Terraform

resource "aws_elasticsearch_domain" "this" {
  domain_name = var.domain_name

  cluster_config {
    instance_type          = var.instance_type
    instance_count         = 3
    zone_awareness_enabled = true

    zone_awareness_config {
      availability_zone_count = 3
    }
  }
}