Controls/EDCA-RES-014.json

{
  "id": "EDCA-RES-014",
  "title": "DAG member distribution is symmetrical across sites",
  "description": "Each site-resilient DAG SHOULD have symmetrical member distribution across its Active Directory sites. Symmetry improves failover behavior by distributing load and activation capacity evenly across failure domains.",
  "verify": true,
  "subject": "Organization",
  "category": "Resilience",
  "severity": "Medium",
  "severityWeight": 6,
  "frameworks": [
    "Best Practice"
  ],
  "references": [
    {
      "name": "Exchange Server Preferred Architecture: DAG configuration",
      "url": "https://learn.microsoft.com/en-us/exchange/plan-and-deploy/deployment-ref/preferred-architecture"
    },
    {
      "name": "Database availability groups (DAGs)",
      "url": "https://learn.microsoft.com/en-us/exchange/high-availability/database-availability-groups/database-availability-groups"
    }
  ],
  "remediation": {
    "automatable": false,
    "description": "Rebalance DAG membership so each participating site hosts an equal number of DAG members.",
    "scriptTemplate": "# Diagnose: Show DAG member counts by site\nGet-ExchangeServer | Where-Object { $_.MemberOfDAG } | Group-Object MemberOfDAG, Site | Select-Object Name, Count | Sort-Object Name | Format-Table -AutoSize"
  },
  "considerations": "If no DAG is deployed, this control is not applicable and should report Skipped. This control validates symmetry for DAGs that span two or more sites; single-site DAGs are treated as non-compliant with site-resilient symmetry guidance.",
  "roles": [
    "Mailbox"
  ]
}