# Pattern: Active Data Guard HA/DR
# Composable architecture block for Oracle Database high availability

pattern:
  name: "Active Data Guard"
  id: active_data_guard
  category: database-ha
  applies_to: [adb_s, adb_d, dbcs, exacs]

description: |
  Oracle Active Data Guard provides real-time data protection with a standby database
  that can be used for read-only queries, reporting, and backups while maintaining
  synchronous or asynchronous replication from the primary.

variants:
  - id: adg_same_region
    name: "Same-Region ADG (HA)"
    topology: "Primary + Standby in same region, different ADs or FDs"
    rpo: "0 (synchronous)"
    rto: "< 30 seconds (automatic failover with FSFO)"
    use_when:
      - "99.99% SLA requirement"
      - "Zero RPO mandatory"
      - "Read-only offload needed"

  - id: adg_cross_region
    name: "Cross-Region ADG (DR)"
    topology: "Primary in Region A, Standby in Region B"
    rpo: "> 0 (asynchronous, typically seconds to minutes)"
    rto: "Minutes to 1 hour depending on automation"
    use_when:
      - "Regional disaster recovery required"
      - "RPO of seconds acceptable"
      - "Regulatory requirement for geo-separation"

  - id: adg_hybrid
    name: "Same-Region HA + Cross-Region DR"
    topology: "Primary + Local Standby (sync) + Remote Standby (async)"
    rpo: "0 local, seconds remote"
    rto: "< 30s local, minutes remote"
    use_when:
      - "Maximum protection: HA + DR"
      - "Mission-critical workloads"

preconditions:
  - "Oracle Database Enterprise Edition with Active Data Guard option"
  - "BYOL: customer must have ADG license or ULA"
  - "License Included: ADG included with ADB-S, ExaCS EE-HP/EE-EP"
  - "For ADB-S: Autonomous Data Guard (managed, no manual config)"

implied_services:
  - service: data_guard
  - service: dns_traffic_management
    reason: "DNS failover for application connection string update"
    when: "cross_region"
  - service: oci_notifications
    reason: "Alert on failover events"

conflicts:
  - pattern: "backup_restore_only"
    reason: "ADG provides real-time replication; backup-restore is a subset"

cost_impact:
  - "Standby database incurs full compute + storage cost"
  - "For ADB-S: standby OCPUs billed at same rate"
  - "Cross-region: additional network egress for redo transport"
  - "BYOL: ADG license required (included in EE-EP)"

sizing_rules:
  - "Standby must be same shape/OCPU as primary for failover"
  - "For read-only offload: standby can handle ~80% of primary read capacity"
  - "Network bandwidth for redo: estimate 10-50 Mbps per 10K TPS (varies by workload)"

references:
  - "https://docs.oracle.com/en/cloud/paas/autonomous-database/adbsa/autonomous-data-guard.html"
  - "https://docs.oracle.com/en/database/oracle/oracle-database/19/sbydb/"