# Multi-Region Deployment Strategy

## Executive Summary

This document outlines the comprehensive multi-region deployment architecture for Mahavishnu, designed to achieve 99.99% availability across global regions while maintaining data sovereignty compliance and optimizing costs.

**Key Objectives:**
- 99.99% availability SLA across all regions
- <5 minute RTO (Recovery Time Objective)
- <1 minute RPO (Recovery Point Objective)
- GDPR, HIPAA, and SOC2 compliance
- 30%+ cost optimization through regional arbitrage
- Zero data loss with multi-master replication

## Architecture Overview

### Deployment Pattern: Active-Active Multi-Region

Mahavishnu uses an **active-active** deployment pattern where all regions serve traffic simultaneously, providing:

- **Zero downtime** during regional failures
- **Low latency** for global users
- **Load distribution** across regions
- **Graceful degradation** during partial outages

### Primary Regions

| Region | Provider | Location | Role | Services |
|--------|----------|----------|------|----------|
| **us-east-1** | AWS | N. Virginia | Primary | All services, master databases |
| **eu-west-1** | AWS | Ireland | Primary | GDPR compliance, European traffic |
| **ap-southeast-1** | AWS | Singapore | Primary | Asia-Pacific traffic |
| **us-central1** | GCP | Iowa | Backup | Disaster recovery, analytics |
| **europe-west1** | GCP | Belgium | Backup | European DR, compliance backup |
| **asia-southeast1** | GCP | Singapore | Backup | Asia-Pacific DR |
| **eastus** | Azure | Virginia | Multi-cloud | Hybrid scenarios, backup |
| **westeurope** | Azure | Netherlands | Multi-cloud | European hybrid |
| **southeastasia** | Azure | Singapore | Multi-cloud | Asia-Pacific hybrid |

## 1. Cross-Region Data Replication

### 1.1 Database Replication Strategy

#### PostgreSQL Multi-Master (Active-Active)

**Technology:** PostgreSQL with Bi-Directional Replication (BDR) or Citus

```
us-east-1 (Primary) ←→ eu-west-1 (Primary) ←→ ap-southeast-1 (Primary)
        ↓                     ↓                        ↓
   us-central1 (Read Replica)  europe-west1 (Read)  asia-southeast1 (Read)
```

**Configuration:**

```yaml
database:
  postgresql:
    mode: multi_master
    primary_regions:
      - region: us-east-1
        endpoint: postgres-primary-us.aws.example.com:5432
        role: writer
      - region: eu-west-1
        endpoint: postgres-primary-eu.aws.example.com:5432
        role: writer
      - region: ap-southeast-1
        endpoint: postgres-primary-ap.aws.example.com:5432
        role: writer
    replication:
      method: logical
      slots: 10
      lag_tolerance_ms: 100
      conflict_resolution: last_write_wins
    backup:
      retention_days: 30
      point_in_time_recovery: true
      cross_region_copy: true
```

**Replication Topology:**

1. **Write Path:** Application writes to local region primary
2. **Replication:** Changes streamed to other primaries within 100ms
3. **Conflict Resolution:** Last-write-wins with timestamp ordering
4. **Read Path:** Applications read from local region (low latency)

#### Conflict Resolution Strategies

```python
# mahavishnu/core/replication/conflict_resolver.py

from enum import Enum
from datetime import datetime
from typing import Any, Dict

class ConflictResolutionStrategy(Enum):
    LAST_WRITE_WINS = "last_write_wins"
    FIRST_WRITE_WINS = "first_write_wins"
    CUSTOM = "custom"

class MultiMasterConflictResolver:
    """Resolves conflicts in multi-master database replication."""

    def __init__(
        self,
        strategy: ConflictResolutionStrategy = ConflictResolutionStrategy.LAST_WRITE_WINS,
        custom_resolver: callable = None,
    ):
        self.strategy = strategy
        self.custom_resolver = custom_resolver

    def resolve(
        self,
        record_id: str,
        conflicting_versions: list[Dict[str, Any]]
    ) -> Dict[str, Any]:
        """Resolve conflicting record versions.

        Args:
            record_id: Unique record identifier
            conflicting_versions: List of conflicting record versions with metadata

        Returns:
            Resolved record version
        """
        if self.strategy == ConflictResolutionStrategy.LAST_WRITE_WINS:
            return self._last_write_wins(conflicting_versions)
        elif self.strategy == ConflictResolutionStrategy.FIRST_WRITE_WINS:
            return self._first_write_wins(conflicting_versions)
        elif self.strategy == ConflictResolutionStrategy.CUSTOM:
            return self.custom_resolver(conflicting_versions)
        else:
            raise ValueError(f"Unknown strategy: {self.strategy}")

    def _last_write_wins(self, versions: list[Dict]) -> Dict:
        """Select version with latest timestamp."""
        return max(versions, key=lambda v: v.get("updated_at", datetime.min))

    def _first_write_wins(self, versions: list[Dict]) -> Dict:
        """Select version with earliest timestamp."""
        return min(versions, key=lambda v: v.get("created_at", datetime.max))
```

### 1.2 Cache Replication

#### Redis Cluster with Cross-Region Replication

**Architecture:**

```
us-east-1: Redis Cluster (3 master + 3 replica)
    ↓ (cross-region replication)
eu-west-1: Redis Cluster (3 master + 3 replica)
    ↓ (cross-region replication)
ap-southeast-1: Redis Cluster (3 master + 3 replica)
```

**Configuration:**

```yaml
cache:
  redis:
    mode: cluster
    cross_region_replication: true
    replication_lag_ms: 50
    eviction_policy: allkeys-lru
    persistence:
      enabled: true
      rdb_enabled: true
      aof_enabled: true
      snapshot_interval: 900  # 15 minutes
    tls: true
    auth: true
```

**Replication Strategy:**

1. **Write:** Write to local Redis cluster
2. **Async Replication:** Replicate to other regions within 50ms
3. **Read:** Read from local cluster
4. **Failover:** Promote replica if master fails

#### Cache Invalidation Strategy

```python
# mahavishnu/core/cache/invalidation.py

from typing import List, Set
from dataclasses import dataclass
import asyncio

@dataclass
class CacheInvalidationEvent:
    """Cache invalidation event."""
    key: str
    region: str
    timestamp: float
    version: int

class CrossRegionCacheInvalidator:
    """Invalidates cache across all regions."""

    def __init__(self, regions: List[str], message_bus):
        self.regions = regions
        self.message_bus = message_bus

    async def invalidate(self, key: str, source_region: str):
        """Invalidate cache key across all regions."""
        event = CacheInvalidationEvent(
            key=key,
            region=source_region,
            timestamp=asyncio.get_event_loop().time(),
            version=1,
        )

        # Publish invalidation event to all regions
        await self.message_bus.publish(
            topic="cache_invalidation",
            message=event,
            regions=self.regions,
        )

    async def subscribe(self, region: str):
        """Subscribe to cache invalidation events."""
        await self.message_bus.subscribe(
            topic="cache_invalidation",
            handler=self._handle_invalidation,
            region=region,
        )

    async def _handle_invalidation(self, event: CacheInvalidationEvent):
        """Handle cache invalidation from another region."""
        # Delete local cache entry
        await self._delete_local(event.key)
```

### 1.3 File Storage Replication

#### S3 Cross-Region Replication (CRR)

**Configuration:**

```yaml
storage:
  s3:
    buckets:
      primary:
        region: us-east-1
        name: mahavishnu-primary-us
      eu:
        region: eu-west-1
        name: mahavishnu-primary-eu
      ap:
        region: ap-southeast-1
        name: mahavishnu-primary-ap
    replication:
      enabled: true
      rules:
        - source: mahavishnu-primary-us
          destinations:
            - mahavishnu-primary-eu
            - mahavishnu-primary-ap
          storage_class: STANDARD
          replication_time: 15 minutes
        - source: mahavishnu-primary-eu
          destinations:
            - mahavishnu-primary-us
            - mahavishnu-primary-ap
          storage_class: STANDARD
          replication_time: 15 minutes
        - source: mahavishnu-primary-ap
          destinations:
            - mahavishnu-primary-us
            - mahavishnu-primary-eu
          storage_class: STANDARD
          replication_time: 15 minutes
    lifecycle:
      transition_to_ia_days: 30
      transition_to_glacier_days: 90
      expiration_days: 365
```

**Replication Rules:**

1. **Immediate Replication:** Critical files replicated within 15 minutes
2. **Event-Driven:** Replication triggered on PUT/POST/DELETE
3. **Versioning:** All versions replicated for point-in-time recovery
4. **Checksum Validation:** MD5/SHA256 verification on replication

### 1.4 Search Index Replication

#### OpenSearch Cross-Cluster Replication (CCR)

**Architecture:**

```
us-east-1: OpenSearch Leader Cluster
    ↓ (cross-cluster replication)
eu-west-1: OpenSearch Follower Cluster
ap-southeast-1: OpenSearch Follower Cluster
```

**Configuration:**

```yaml
opensearch:
  mode: cross_cluster_replication
  leader_cluster:
    region: us-east-1
    endpoint: https://opensearch-leader.aws.example.com:9200
    nodes: 6
  follower_clusters:
    - region: eu-west-1
      endpoint: https://opensearch-follower-eu.aws.example.com:9200
      nodes: 3
      replication_type: push
    - region: ap-southeast-1
      endpoint: https://opensearch-follower-ap.aws.example.com:9200
      nodes: 3
      replication_type: push
  indexes:
    - name: mahavishnu_code
      replication_enabled: true
      read_only_followers: true
    - name: mahavishnu_sessions
      replication_enabled: true
      read_only_followers: false
```

**Replication Strategy:**

1. **Write:** Write to leader cluster (us-east-1)
2. **Replication:** Changes pushed to followers within 1 minute
3. **Read:** Local region reads from follower cluster
4. **Failover:** Promote follower to leader if primary fails

### 1.5 Real-Time Data Synchronization

#### Message Bus with Multi-Region Topics

**Architecture:** Apache Kafka or Google Cloud Pub/Sub with multi-region replication

```yaml
messaging:
  kafka:
    mode: multi_region
    regions:
      - us-east-1
      - eu-west-1
      - ap-southeast-1
    replication_factor: 3
    cross_region_replication: true
    topics:
      - name: workflow_events
        partitions: 12
        replication_factor: 3
        retention_ms: 604800000  # 7 days
      - name: cache_invalidation
        partitions: 6
        replication_factor: 3
        retention_ms: 86400000  # 1 day
      - name: replication_events
        partitions: 6
        replication_factor: 3
        retention_ms: 604800000
    mirror_maker:
      enabled: true
      topics:
        - workflow_events
        - cache_invalidation
        - replication_events
```

**Synchronization Flow:**

1. **Producer:** Publish to local region Kafka cluster
2. **MirrorMaker:** Replicate topics to other regions
3. **Consumer:** Consume from local region (low latency)
4. **Ordering:** Per-partition ordering maintained

## 2. Global Load Balancing

### 2.1 DNS Load Balancing Strategy

#### Multi-Tier DNS Architecture

```
User
  ↓
CloudFlare Enterprise DNS (Global anycast)
  ↓
Route53 Latency-Based Routing (AWS)
  ↓
Regional Load Balancers (ALB/NLB)
  ↓
Kubernetes Ingress (NGINX/Traefik)
  ↓
Application Pods
```

### 2.2 CloudFlare DNS Configuration

**Configuration:**

```yaml
dns:
  cloudflare:
    zone: example.com
    records:
      - name: api
        type: CNAME
        proxied: true
        ttl: 1
        load_balancing: true
        pools:
          - name: us-east
            regions:
              - US
              - CA
              - MX
            origins:
              - name: us-east-1
                address: alb-us-east-1.aws.example.com
                health_check: true
          - name: eu-west
            regions:
              - EU
              - AF
            origins:
              - name: eu-west-1
                address: alb-eu-west-1.aws.example.com
                health_check: true
          - name: ap-southeast
            regions:
              - APAC
              - OCEANIA
            origins:
              - name: ap-southeast-1
                address: alb-ap-southeast-1.aws.example.com
                health_check: true
        steering_policy: latency
        fallback_pool: us-east
```

**Load Balancing Algorithms:**

1. **Latency-Based:** Route to region with lowest latency
2. **Geographic:** Route based on user location
3. **Proximity:** Route to nearest region
4. **Weighted:** Distribute traffic by percentage
5. **Failover:** Automatic failover on health check failure

### 2.3 AWS Route53 Configuration

**Health Checks:**

```yaml
route53:
  health_checks:
    - id: hc-us-east-1
      type: HTTPS
      resource_path: /health
      port: 443
      interval_seconds: 30
      timeout_seconds: 5
      failure_threshold: 3
      regions:
        - us-east-1
    - id: hc-eu-west-1
      type: HTTPS
      resource_path: /health
      port: 443
      interval_seconds: 30
      timeout_seconds: 5
      failure_threshold: 3
      regions:
        - eu-west-1
    - id: hc-ap-southeast-1
      type: HTTPS
      resource_path: /health
      port: 443
      interval_seconds: 30
      timeout_seconds: 5
      failure_threshold: 3
      regions:
        - ap-southeast-1
  records:
    - name: api.example.com
      type: CNAME
      routing_policy: latency
      set_identifier: us-east-1
      alias_target:
        dns_name: alb-us-east-1.aws.example.com
        health_check_id: hc-us-east-1
      region: us-east-1
    - name: api.example.com
      type: CNAME
      routing_policy: latency
      set_identifier: eu-west-1
      alias_target:
        dns_name: alb-eu-west-1.aws.example.com
        health_check_id: hc-eu-west-1
      region: eu-west-1
```

### 2.4 Regional Load Balancers

#### AWS Application Load Balancer (ALB)

**Configuration:**

```yaml
load_balancer:
  type: application
  scheme: internet-facing
  ip_address_type: ipv4
  subnets:
    - subnet-public-us-east-1a
    - subnet-public-us-east-1b
    - subnet-public-us-east-1c
  security_groups:
    - sg-alb
  attributes:
    idle_timeout_seconds: 300
    deletion_protection: true
    http2_enabled: true
    routing_http2_enabled: true
    http_drop_invalid_header_fields: true
    http_drop_invalid_header_fields_enabled: true
  listeners:
    - port: 443
      protocol: HTTPS
      certificates:
        - arn: arn:aws:acm:us-east-1:123456789:certificate/abc123
      default_actions:
        - type: forward
          target_group: tg-mahavishnu
  target_groups:
    - name: tg-mahavishnu
      port: 8080
      protocol: HTTP
      health_check:
        path: /health
        interval_seconds: 30
        timeout_seconds: 5
        healthy_threshold: 2
        unhealthy_threshold: 3
        matcher:
          http_code: "200"
```

### 2.5 Session Affinity

#### Sticky Session Configuration

```yaml
session_affinity:
  enabled: true
  type: application_cookie
  cookie_name: MAHAVISHNU_SESSION
  cookie_duration_seconds: 3600
  fallback: round_robin

load_balancer:
  stickiness:
    enabled: true
    type: app_cookie
    cookie_name: MAHAVISHNU_AFFINITY
    duration_seconds: 3600
```

**Session Replication:**

1. **Session Store:** Redis with cross-region replication
2. **Affinity:** Sticky sessions to same region/pod
3. **Failover:** Session data available in all regions
4. **Consistency:** Strong consistency for session reads

## 3. Data Sovereignty Compliance

### 3.1 GDPR Compliance (EU Data Residency)

#### EU Data Isolation Strategy

```yaml
data_sovereignty:
  gdpr:
    enabled: true
    eu_only_data:
      - user_profiles
      - personal_identifiable_information
      - consent_records
      - analytics_eu_only
    storage_policy:
      eu_data_stored_in:
        - eu-west-1
        - europe-west1
        - westeurope
      replication_allowed: false
      cross_border_transfer: false
    compliance:
      right_to_access: true
      right_to_erasure: true
      right_to_portability: true
      right_to_rectification: true
      data_protection_impact_assessment: true
```

**Implementation:**

```python
# mahavishnu/core/compliance/gdpr_router.py

from enum import Enum
from typing import Optional, List

class DataRegion(Enum):
    US = "us"
    EU = "eu"
    APAC = "apac"
    GLOBAL = "global"

class GDPRCompliantRouter:
    """Routes data requests based on GDPR compliance."""

    EU_REGIONS = ["eu-west-1", "europe-west1", "westeurope"]
    EU_DATA_TYPES = ["user_profiles", "pii", "consent_records"]

    def __init__(self, current_region: str):
        self.current_region = current_region

    def get_storage_region(self, data_type: str, user_region: str) -> str:
        """Determine appropriate storage region for data.

        Args:
            data_type: Type of data being stored
            user_region: User's home region

        Returns:
            Region where data should be stored
        """
        # EU data must stay in EU
        if data_type in self.EU_DATA_TYPES and user_region == "eu":
            return "eu-west-1"

        # Non-EU data can use local region
        return self.current_region

    def can_replicate(self, data_type: str, source_region: str, dest_region: str) -> bool:
        """Check if data replication is compliant with GDPR.

        Args:
            data_type: Type of data being replicated
            source_region: Source region
            dest_region: Destination region

        Returns:
            True if replication is allowed
        """
        # EU data cannot be replicated outside EU
        if data_type in self.EU_DATA_TYPES:
            if source_region in self.EU_REGIONS and dest_region not in self.EU_REGIONS:
                return False

        return True

    def handle_right_to_erasure(self, user_id: str) -> dict:
        """Handle GDPR right to erasure (right to be forgotten).

        Args:
            user_id: User ID to erase

        Returns:
            Erasure results from all regions
        """
        results = {}

        # Erase from all regions
        for region in self.EU_REGIONS:
            results[region] = self._erase_user_data(user_id, region)

        return results

    def _erase_user_data(self, user_id: str, region: str) -> bool:
        """Erase user data from specific region."""
        # Implementation depends on storage backend
        pass
```

### 3.2 Data Localization Requirements

#### Country-Specific Data Residency

```yaml
data_localization:
  countries:
    germany:
      data_residency: eu
      regions_allowed:
        - eu-west-1
        - eu-central-1
      encryption_required: true
      retention_years: 10
    france:
      data_residency: eu
      regions_allowed:
        - eu-west-1
        - eu-south-1
      encryption_required: true
      retention_years: 10
    china:
      data_residency: china
      regions_allowed:
        - cn-north-1
      encryption_required: true
      retention_years: 7
      cross_border_transfer: false
    russia:
      data_residency: russia
      regions_allowed:
        - ru-msk
      encryption_required: true
      retention_years: 5
      localization_required: true
```

### 3.3 Cross-Border Data Transfer Controls

#### Data Transfer Mechanisms

```yaml
data_transfer:
  cross_border:
    enabled: false  # Default: no cross-border transfers
    exceptions:
      - type: explicit_consent
        require_user_consent: true
        consent_language: "I agree to transfer my data outside the EU"
      - type: standard_contractual_clauses
        scc_signed: true
        scc_version: "2021-09-01"
      - type: binding_corporate_rules
        bcr_approved: true
        bcr_expiry: "2025-12-31"
    compliance_frameworks:
      - gdpr_eu_to_us
      - privacy_shield
      - adequacy_decisions
    audit_logging:
      enabled: true
      log_all_transfers: true
      retention_years: 7
```

### 3.4 Regional Data Isolation

#### Database Schema Isolation

```sql
-- Regional partitioning for data isolation

CREATE TABLE users (
    user_id UUID PRIMARY KEY,
    email VARCHAR(255) NOT NULL,
    data_region VARCHAR(10) NOT NULL,  -- 'us', 'eu', 'apac'
    created_at TIMESTAMP DEFAULT NOW(),
    updated_at TIMESTAMP DEFAULT NOW(),
    CHECK (
        (data_region = 'eu' AND email IS NOT NULL) OR
        (data_region = 'us' AND email IS NOT NULL) OR
        (data_region = 'apac' AND email IS NOT NULL)
    )
);

CREATE INDEX idx_users_data_region ON users(data_region);
CREATE INDEX idx_users_email ON users(email);

-- Row-Level Security (RLS) for data isolation

ALTER TABLE users ENABLE ROW LEVEL SECURITY;

CREATE POLICY eu_data_isolation ON users
    FOR ALL
    TO mahavishnu_app
    USING (
        data_region = 'eu' AND current_setting('app.region') = 'eu-west-1'
    );

CREATE POLICY us_data_isolation ON users
    FOR ALL
    TO mahavishnu_app
    USING (
        data_region = 'us' AND current_setting('app.region') = 'us-east-1'
    );
```

### 3.5 Compliance Audit Logging

```yaml
audit_logging:
  enabled: true
  log_all_access: true
  log_data_transfers: true
  log_admin_actions: true
  retention:
    years: 7
    immutable: true
  format:
    timestamp: true
    user_id: true
    action: true
    resource: true
    region: true
    outcome: true
    ip_address: true
  export:
    enabled: true
    formats:
      - json
      - csv
    encryption: true
```

**Implementation:**

```python
# mahavishnu/core/compliance/audit_logger.py

from dataclasses import dataclass
from datetime import datetime
from typing import Optional
import json

@dataclass
class AuditEvent:
    """Compliance audit event."""
    timestamp: datetime
    user_id: str
    action: str
    resource: str
    region: str
    outcome: str  # 'success' or 'failure'
    ip_address: str
    details: dict

class ComplianceAuditLogger:
    """Logs compliance-related events for audit purposes."""

    def __init__(self, storage_backend):
        self.storage = storage_backend

    async def log(self, event: AuditEvent):
        """Log audit event to immutable storage."""
        # Serialize event
        event_data = {
            "timestamp": event.timestamp.isoformat(),
            "user_id": event.user_id,
            "action": event.action,
            "resource": event.resource,
            "region": event.region,
            "outcome": event.outcome,
            "ip_address": event.ip_address,
            "details": event.details,
        }

        # Write to immutable storage (WORM - Write Once Read Many)
        await self.storage.write(
            table="audit_log",
            data=event_data,
            immutable=True,
        )

        # Also send to SIEM/Splunk
        await self._send_to_siem(event_data)

    async def query(self, filters: dict) -> list[AuditEvent]:
        """Query audit log with filters."""
        return await self.storage.query(
            table="audit_log",
            filters=filters,
        )

    async def export(self, start_date: datetime, end_date: datetime, format: str = "json") -> bytes:
        """Export audit log for compliance reporting."""
        events = await self.storage.query(
            table="audit_log",
            filters={
                "start_date": start_date,
                "end_date": end_date,
            },
        )

        if format == "json":
            return json.dumps(events, indent=2).encode()
        elif format == "csv":
            return self._to_csv(events)
        else:
            raise ValueError(f"Unsupported format: {format}")
```

## 4. Regional Failover Procedures

### 4.1 Automatic Failover Architecture

#### Health Check Monitoring

```yaml
health_checks:
  regional:
    enabled: true
    interval_seconds: 10
    timeout_seconds: 5
    failure_threshold: 3
    success_threshold: 2
    endpoints:
      - path: /health
        expected_status: 200
        expected_body: '{"status":"healthy"}'
      - path: /api/v1/ping
        expected_status: 200
      - path: /api/v1/workflows
        expected_status: 200
  database:
    enabled: true
    check_replication_lag: true
    max_replication_lag_ms: 500
    check_disk_space: true
    min_disk_space_percent: 20
  dependencies:
    - service: opensearch
      endpoint: https://opensearch:9200/_cluster/health
    - service: redis
      endpoint: redis://redis:6379/ping
    - service: kafka
      endpoint: kafka://kafka:9092
```

#### Failover Decision Engine

```python
# mahavishnu/core/failover/decision_engine.py

from dataclasses import dataclass
from enum import Enum
from typing import List, Dict, Optional
import asyncio

class FailoverDecision(Enum):
    NO_FAILOVER = "no_failover"
    IMMEDIATE_FAILOVER = "immediate_failover"
    GRACEFUL_FAILOVER = "graceful_failover"
    MANUAL_INTERVENTION = "manual_intervention"

@dataclass
class HealthStatus:
    """Health status of a region."""
    region: str
    healthy: bool
    score: float  # 0.0 to 1.0
    failed_checks: List[str]
    last_check_time: float

@dataclass
class FailoverPlan:
    """Failover plan for a region."""
    source_region: str
    target_region: str
    decision: FailoverDecision
    reason: str
    estimated_duration_seconds: int
    data_loss_risk: str  # 'none', 'minimal', 'moderate', 'high'

class RegionalFailoverEngine:
    """Makes and executes failover decisions based on health monitoring."""

    def __init__(
        self,
        regions: List[str],
        health_checker,
        load_balancer,
        database_failover,
    ):
        self.regions = regions
        self.health_checker = health_checker
        self.load_balancer = load_balancer
        self.database_failover = database_failover
        self.failover_in_progress = False

    async def monitor_and_decide(self) -> Optional[FailoverPlan]:
        """Monitor all regions and decide if failover is needed."""
        health_statuses = await self._check_all_regions()

        # Check if any region is unhealthy
        unhealthy_regions = [
            r for r in health_statuses
            if not r.healthy
        ]

        if not unhealthy_regions:
            return None  # All regions healthy

        # Generate failover plan for each unhealthy region
        plans = []
        for region in unhealthy_regions:
            plan = await self._create_failover_plan(region, health_statuses)
            if plan:
                plans.append(plan)

        # Execute plans (most critical first)
        if plans:
            plans.sort(key=lambda p: p.data_loss_risk)
            return plans[0]

        return None

    async def _check_all_regions(self) -> List[HealthStatus]:
        """Check health of all regions."""
        tasks = [
            self.health_checker.check_region(region)
            for region in self.regions
        ]
        return await asyncio.gather(*tasks)

    async def _create_failover_plan(
        self,
        failed_region: str,
        all_statuses: List[HealthStatus],
    ) -> Optional[FailoverPlan]:
        """Create failover plan for failed region.

        Args:
            failed_region: Region that failed
            all_statuses: Health status of all regions

        Returns:
            Failover plan or None if no healthy target available
        """
        # Find healthiest target region
        target_region = max(
            [r for r in all_statuses if r.region != failed_region],
            key=lambda r: r.score,
            default=None,
        )

        if not target_region or target_region.score < 0.7:
            # No healthy target region
            return FailoverPlan(
                source_region=failed_region,
                target_region="",
                decision=FailoverDecision.MANUAL_INTERVENTION,
                reason="No healthy target region available",
                estimated_duration_seconds=0,
                data_loss_risk="high",
            )

        # Determine failover decision
        failed_status = next(r for r in all_statuses if r.region == failed_region)

        if failed_status.score < 0.2:
            decision = FailoverDecision.IMMEDIATE_FAILOVER
            reason = "Complete region failure"
        elif failed_status.score < 0.5:
            decision = FailoverDecision.GRACEFUL_FAILOVER
            reason = "Partial region failure"
        else:
            decision = FailoverDecision.NO_FAILOVER
            reason = "Region degraded but operational"

        return FailoverPlan(
            source_region=failed_region,
            target_region=target_region.region,
            decision=decision,
            reason=reason,
            estimated_duration_seconds=300,  # 5 minutes
            data_loss_risk="none",  # Multi-master replication
        )

    async def execute_failover(self, plan: FailoverPlan) -> bool:
        """Execute failover plan.

        Args:
            plan: Failover plan to execute

        Returns:
            True if failover successful
        """
        if plan.decision == FailoverDecision.NO_FAILOVER:
            return True

        if plan.decision == FailoverDecision.MANUAL_INTERVENTION:
            # Alert on-call engineer
            await self._alert_on_call(plan)
            return False

        self.failover_in_progress = True

        try:
            # Step 1: Stop new traffic to failed region
            await self.load_balancer.disable_region(plan.source_region)

            # Step 2: Promote target region (if needed)
            await self.database_failover.promote_region(plan.target_region)

            # Step 3: Update DNS to route to target region
            await self.load_balancer.failover_dns(
                from_region=plan.source_region,
                to_region=plan.target_region,
            )

            # Step 4: Verify target region is healthy
            health = await self.health_checker.check_region(plan.target_region)
            if not health.healthy:
                raise Exception(f"Target region {plan.target_region} is unhealthy")

            # Step 5: Monitor for stability
            await asyncio.sleep(60)
            health = await self.health_checker.check_region(plan.target_region)
            if not health.healthy:
                raise Exception(f"Target region {plan.target_region} unstable after failover")

            return True

        except Exception as e:
            # Rollback and alert
            await self._rollback_failover(plan)
            await self._alert_on_call(plan, error=str(e))
            return False

        finally:
            self.failover_in_progress = False

    async def _alert_on_call(self, plan: FailoverPlan, error: Optional[str] = None):
        """Alert on-call engineer about failover."""
        # Send PagerDuty alert
        message = f"Failover required: {plan.source_region} -> {plan.target_region}"
        if error:
            message += f"\nError: {error}"

        # Implementation depends on alerting system
        pass

    async def _rollback_failover(self, plan: FailoverPlan):
        """Rollback failed failover attempt."""
        await self.load_balancer.enable_region(plan.source_region)
```

### 4.2 Traffic Shifting Strategies

#### Blue-Green Deployment

```yaml
traffic_shifting:
  strategy: blue_green
  blue_environment:
    region: us-east-1
    traffic_percentage: 100
  green_environment:
    region: us-east-1-new
    traffic_percentage: 0
  shift_schedule:
    - step: 1
      traffic_percentage: 10
      duration_minutes: 5
      health_check_required: true
    - step: 2
      traffic_percentage: 25
      duration_minutes: 10
      health_check_required: true
    - step: 3
      traffic_percentage: 50
      duration_minutes: 15
      health_check_required: true
    - step: 4
      traffic_percentage: 100
      duration_minutes: 30
      health_check_required: true
  rollback_on_failure: true
  rollback_threshold_percent: 5  # Rollback if error rate > 5%
```

#### Canary Deployment

```yaml
traffic_shifting:
  strategy: canary
  baseline:
    region: us-east-1
    version: v1.0.0
    traffic_percentage: 90
  canary:
    region: us-east-1
    version: v1.1.0
    traffic_percentage: 10
  metrics:
    - name: error_rate
      threshold: 0.01  # 1%
      comparison: less_than
    - name: latency_p95
      threshold: 500  # ms
      comparison: less_than
    - name: throughput
      threshold: 1000  # req/s
      comparison: greater_than
  auto_promote: true
  promote_after_minutes: 30
  rollback_on_failure: true
```

### 4.3 Split-Brain Prevention

#### Distributed Locking with Consul

```yaml
split_brain_prevention:
  enabled: true
  mechanism: consul
  consul:
    address: consul.service.consul:8500
    session_ttl: 30s
    lock_key: "mahavishnu/regional_failover_lock"
    retry_interval: 5s
  leadership:
    election_timeout: 10s
    heartbeat_interval: 5s
    pre_vote: true
  quorum:
    enabled: true
    size: 3  # Need 2/3 agreement
    regions:
      - us-east-1
      - eu-west-1
      - ap-southeast-1
```

**Implementation:**

```python
# mahavishnu/core/failover/split_brain_prevention.py

import asyncio
from typing import Optional
import consul

class DistributedLockManager:
    """Manages distributed locks to prevent split-brain scenarios."""

    def __init__(self, consul_address: str, region: str):
        self.consul = consul.Consul(host=consul_address)
        self.region = region
        self.session_id: Optional[str] = None

    async def acquire_failover_lock(self) -> bool:
        """Acquire distributed lock for failover operations.

        Returns:
            True if lock acquired successfully
        """
        # Create session
        self.session_id = self.consul.session.create(
            name=f"failover_lock_{self.region}",
            ttl=30,  # 30 seconds
            behavior="delete",
        )

        # Acquire lock
        acquired = self.consul.kv.put(
            key="mahavishnu/regional_failover_lock",
            value=self.region.encode(),
            acquire=self.session_id,
        )

        return acquired

    async def release_failover_lock(self):
        """Release distributed lock."""
        if self.session_id:
            self.consul.session.destroy(self.session_id)
            self.session_id = None

    async def maintain_heartbeat(self):
        """Maintain heartbeat to keep lock alive."""
        while self.session_id:
            # Renew session
            self.consul.session.renew(self.session_id)
            await asyncio.sleep(10)  # Heartbeat every 10 seconds

    async def is_leader(self) -> bool:
        """Check if this region is the leader.

        Returns:
            True if this region holds the lock
        """
        index, data = self.consul.kv.get("mahavishnu/regional_failover_lock")

        if data and data['Value']:
            leader_region = data['Value'].decode()
            return leader_region == self.region

        return False

    async def wait_for_leadership(self, timeout: int = 60) -> bool:
        """Wait for this region to become leader.

        Args:
            timeout: Maximum seconds to wait

        Returns:
            True if leadership acquired
        """
        start_time = asyncio.get_event_loop().time()

        while True:
            if await self.acquire_failover_lock():
                return True

            if asyncio.get_event_loop().time() - start_time > timeout:
                return False

            await asyncio.sleep(5)
```

### 4.4 Failback Procedures

```yaml
failback:
  enabled: true
  auto_failback: false  # Require manual approval
  health_check_duration: 300  # Monitor for 5 minutes before failback
  steps:
    - name: verify_original_region_health
      type: health_check
      target_region: original
      threshold: 0.9
    - name: sync_data
      type: data_sync
      source_region: failover
      target_region: original
    - name: drain_failover_region
      type: drain_traffic
      region: failover
      duration_seconds: 300
    - name: enable_original_region
      type: enable_traffic
      region: original
      traffic_percentage: 100
    - name: verify_failback
      type: health_check
      target_region: original
      threshold: 0.95
```

## 5. Multi-Region Configuration Management

### 5.1 Region-Specific Configuration

```yaml
# Configuration hierarchy
# 1. Global defaults (config/global.yaml)
# 2. Region-specific (config/{region}.yaml)
# 3. Environment-specific (config/{region}/{environment}.yaml)
# 4. Environment variables (MAHAVISHNU_{REGION}__{FIELD})

# config/global.yaml
global:
  app_name: mahavishnu
  version: 1.0.0
  log_level: INFO

# config/us-east-1.yaml
us-east-1:
  region: us-east-1
  provider: aws
  database:
    endpoint: postgres-us-east-1.aws.example.com
    port: 5432
  cache:
    endpoint: redis-us-east-1.aws.example.com
    port: 6379
  storage:
    bucket: mahavishnu-us-east-1

# config/eu-west-1.yaml
eu-west-1:
  region: eu-west-1
  provider: aws
  data_residency: eu
  database:
    endpoint: postgres-eu-west-1.aws.example.com
    port: 5432
  cache:
    endpoint: redis-eu-west-1.aws.example.com
    port: 6379
  storage:
    bucket: mahavishnu-eu-west-1
  compliance:
    gdpr_enabled: true
    data_localization: true
```

**Configuration Loader:**

```python
# mahavishnu/core/config/multi_region.py

from pathlib import Path
from typing import Dict, Any
import yaml

class MultiRegionConfigLoader:
    """Loads configuration for multi-region deployments."""

    def __init__(self, config_dir: Path, region: str, environment: str = "production"):
        self.config_dir = config_dir
        self.region = region
        self.environment = environment

    def load(self) -> Dict[str, Any]:
        """Load configuration with proper precedence.

        Returns:
            Merged configuration dictionary
        """
        config = {}

        # 1. Load global defaults
        global_config = self._load_yaml("global.yaml")
        config.update(global_config)

        # 2. Load region-specific config
        region_config = self._load_yaml(f"{self.region}.yaml")
        config = self._deep_merge(config, region_config)

        # 3. Load environment-specific config
        env_config = self._load_yaml(f"{self.region}/{self.environment}.yaml")
        config = self._deep_merge(config, env_config)

        # 4. Apply environment variable overrides
        config = self._apply_env_overrides(config)

        return config

    def _load_yaml(self, filename: str) -> Dict[str, Any]:
        """Load YAML file."""
        path = self.config_dir / filename
        if not path.exists():
            return {}

        with open(path) as f:
            return yaml.safe_load(f) or {}

    def _deep_merge(self, base: Dict, override: Dict) -> Dict:
        """Deep merge two dictionaries."""
        result = base.copy()

        for key, value in override.items():
            if key in result and isinstance(result[key], dict) and isinstance(value, dict):
                result[key] = self._deep_merge(result[key], value)
            else:
                result[key] = value

        return result

    def _apply_env_overrides(self, config: Dict) -> Dict:
        """Apply environment variable overrides."""
        import os

        prefix = f"MAHAVISHNU_{self.region.upper()}_"

        for key, value in os.environ.items():
            if key.startswith(prefix):
                # MAHAVISHNU_US_EAST_1__DATABASE__PORT
                config_key = key[len(prefix):].lower().split("__")
                self._set_nested_value(config, config_key, value)

        return config

    def _set_nested_value(self, config: Dict, keys: list, value: Any):
        """Set nested value in dictionary."""
        if len(keys) == 1:
            config[keys[0]] = value
        else:
            if keys[0] not in config:
                config[keys[0]] = {}
            self._set_nested_value(config[keys[0]], keys[1:], value)
```

### 5.2 Configuration Synchronization

```yaml
config_sync:
  enabled: true
  strategy: pull
  interval_seconds: 300
  source: config_store
  destinations:
    - type: s3
      bucket: mahavishnu-config-us-east-1
      region: us-east-1
    - type: s3
      bucket: mahavishnu-config-eu-west-1
      region: eu-west-1
    - type: s3
      bucket: mahavishnu-config-ap-southeast-1
      region: ap-southeast-1
  validation:
    enabled: true
    schema_version: 1.0
    reject_on_error: true
```

### 5.3 Secret Management per Region

```yaml
secrets:
  manager: aws_secrets_manager  # or: vault, gcp_secret_manager, azure_key_vault
  regions:
    us-east-1:
      endpoint: https://secretsmanager.us-east-1.amazonaws.com
      prefix: mahavishnu/us-east-1/
    eu-west-1:
      endpoint: https://secretsmanager.eu-west-1.amazonaws.com
      prefix: mahavishnu/eu-west-1/
    ap-southeast-1:
      endpoint: https://secretsmanager.ap-southeast-1.amazonaws.com
      prefix: mahavishnu/ap-southeast-1/
  rotation:
    enabled: true
    interval_days: 90
    auto_rotate: true
  replication:
    enabled: false  # Never replicate secrets across regions
  audit:
    enabled: true
    log_all_access: true
```

**Secret Manager Integration:**

```python
# mahavishnu/core/secrets/region_manager.py

from typing import Dict, Optional
import boto3
import json

class RegionalSecretManager:
    """Manages secrets for multi-region deployment."""

    def __init__(self, region: str):
        self.region = region
        self.client = boto3.client(
            'secretsmanager',
            region_name=region,
        )

    async def get_secret(self, secret_name: str) -> Optional[Dict]:
        """Get secret from regional secret manager.

        Args:
            secret_name: Name of secret (without prefix)

        Returns:
            Secret value as dictionary or None if not found
        """
        full_name = f"mahavishnu/{self.region}/{secret_name}"

        try:
            response = self.client.get_secret_value(SecretId=full_name)
            secret_string = response['SecretString']
            return json.loads(secret_string)
        except self.client.exceptions.ResourceNotFoundException:
            return None

    async def set_secret(self, secret_name: str, value: Dict):
        """Set secret in regional secret manager.

        Args:
            secret_name: Name of secret (without prefix)
            value: Secret value as dictionary
        """
        full_name = f"mahavishnu/{self.region}/{secret_name}"
        secret_string = json.dumps(value)

        self.client.put_secret_value(
            SecretId=full_name,
            SecretString=secret_string,
        )

    async def rotate_secret(self, secret_name: str):
        """Trigger secret rotation.

        Args:
            secret_name: Name of secret to rotate
        """
        full_name = f"mahavishnu/{self.region}/{secret_name}"

        self.client.rotate_secret(
            SecretId=full_name,
        )
```

### 5.4 Configuration Drift Detection

```yaml
drift_detection:
  enabled: true
  interval_hours: 1
  baseline: config_store
  comparison:
    enabled: true
    ignore:
      - database.password  # Ignore secret values
      - cache.auth_token
  alerting:
    enabled: true
    on_drift_detected: alert_and_block
  auto_remediation:
    enabled: false  # Manual review required
```

**Drift Detection Implementation:**

```python
# mahavishnu/core/config/drift_detection.py

from dataclasses import dataclass
from typing import Dict, List
import asyncio

@dataclass
class ConfigDifference:
    """Configuration difference between regions."""
    key: str
    region_a: str
    region_b: str
    value_a: any
    value_b: any
    severity: str  # 'critical', 'warning', 'info'

class ConfigDriftDetector:
    """Detects configuration drift across regions."""

    def __init__(
        self,
        regions: List[str],
        config_loader,
        alerting,
    ):
        self.regions = regions
        self.config_loader = config_loader
        self.alerting = alerting

    async def detect_drift(self) -> List[ConfigDifference]:
        """Detect configuration drift across all regions.

        Returns:
            List of configuration differences
        """
        # Load config from all regions
        configs = {}
        for region in self.regions:
            configs[region] = await self._load_region_config(region)

        # Compare configs
        differences = []
        for i, region_a in enumerate(self.regions):
            for region_b in self.regions[i+1:]:
                differences.extend(
                    self._compare_configs(
                        configs[region_a],
                        configs[region_b],
                        region_a,
                        region_b,
                    )
                )

        # Alert if critical differences found
        critical_diffs = [d for d in differences if d.severity == 'critical']
        if critical_diffs:
            await self.alerting.send_alert(
                severity="critical",
                message=f"Configuration drift detected: {len(critical_diffs)} critical differences",
                details=critical_diffs,
            )

        return differences

    async def _load_region_config(self, region: str) -> Dict:
        """Load configuration from region."""
        return await self.config_loader.load(region=region)

    def _compare_configs(
        self,
        config_a: Dict,
        config_b: Dict,
        region_a: str,
        region_b: str,
        path: str = "",
    ) -> List[ConfigDifference]:
        """Compare two configuration dictionaries.

        Args:
            config_a: First config
            config_b: Second config
            region_a: Region A name
            region_b: Region B name
            path: Current path in config

        Returns:
            List of differences
        """
        differences = []

        # Check all keys in config_a
        for key in config_a:
            current_path = f"{path}.{key}" if path else key

            if key not in config_b:
                differences.append(ConfigDifference(
                    key=current_path,
                    region_a=region_a,
                    region_b=region_b,
                    value_a=config_a[key],
                    value_b=None,
                    severity="warning",
                ))
                continue

            # Compare values
            value_a = config_a[key]
            value_b = config_b[key]

            if isinstance(value_a, dict) and isinstance(value_b, dict):
                # Recursively compare nested dicts
                differences.extend(
                    self._compare_configs(
                        value_a,
                        value_b,
                        region_a,
                        region_b,
                        current_path,
                    )
                )
            elif value_a != value_b:
                # Determine severity
                severity = self._determine_severity(current_path, value_a, value_b)

                differences.append(ConfigDifference(
                    key=current_path,
                    region_a=region_a,
                    region_b=region_b,
                    value_a=value_a,
                    value_b=value_b,
                    severity=severity,
                ))

        # Check for keys only in config_b
        for key in config_b:
            if key not in config_a:
                current_path = f"{path}.{key}" if path else key
                differences.append(ConfigDifference(
                    key=current_path,
                    region_a=region_a,
                    region_b=region_b,
                    value_a=None,
                    value_b=config_b[key],
                    severity="warning",
                ))

        return differences

    def _determine_severity(self, key: str, value_a: any, value_b: any) -> str:
        """Determine severity of configuration difference."""
        # Critical differences
        critical_keys = [
            'database.endpoint',
            'cache.endpoint',
            'region',
            'compliance.gdpr_enabled',
        ]

        if key in critical_keys:
            return 'critical'

        # Warning differences
        warning_keys = [
            'log_level',
            'timeout',
            'max_connections',
        ]

        if key in warning_keys:
            return 'warning'

        # Info differences
        return 'info'
```

## 6. Implementation Roadmap

### Phase 1: Foundation (Weeks 1-2)
- [ ] Set up regional infrastructure (VPC, subnets, security groups)
- [ ] Deploy regional databases with replication
- [ ] Configure Redis clusters with cross-region replication
- [ ] Set up S3 buckets with cross-region replication
- [ ] Deploy OpenSearch with cross-cluster replication

### Phase 2: Load Balancing (Weeks 3-4)
- [ ] Configure CloudFlare DNS with global load balancing
- [ ] Set up Route53 with latency-based routing
- [ ] Deploy regional ALBs/NLBs
- [ ] Configure health checks
- [ ] Implement session affinity

### Phase 3: Failover Automation (Weeks 5-6)
- [ ] Implement health check monitoring
- [ ] Build failover decision engine
- [ ] Configure automatic failover
- [ ] Implement split-brain prevention
- [ ] Create failback procedures

### Phase 4: Compliance (Weeks 7-8)
- [ ] Implement GDPR data isolation
- [ ] Configure data localization
- [ ] Set up audit logging
- [ ] Implement cross-border transfer controls
- [ ] Create compliance dashboards

### Phase 5: Configuration Management (Weeks 9-10)
- [ ] Set up regional configuration management
- [ ] Implement configuration synchronization
- [ ] Deploy regional secret managers
- [ ] Implement drift detection
- [ ] Create configuration validation

### Phase 6: Testing & Validation (Weeks 11-12)
- [ ] Conduct regional failover drills
- [ ] Test disaster recovery procedures
- [ ] Validate compliance requirements
- [ ] Performance testing across regions
- [ ] Security audit and penetration testing

## 7. Cost Optimization Strategies

### 7.1 Regional Cost Arbitrage

```yaml
cost_optimization:
  regional_arbitrage:
    enabled: true
    compute:
      cheap_regions:
        - us-west-2  # Oregon
        - eu-central-1  # Frankfurt
        - ap-south-1  # Mumbai
      expensive_regions:
        - us-east-1  # N. Virginia
        - eu-west-1  # Ireland
      strategy:
        - type: batch_processing
          regions: cheap_regions
          workloads:
            - background_jobs
            - analytics
            - report_generation
        - type: latency_sensitive
          regions: expensive_regions
          workloads:
            - api_servers
            - web_serving
            - real_time_processing
    storage:
      cheap_regions:
        - us-east-2  # Ohio
        - eu-west-2  # London
      strategy:
        - type: archive
          regions: cheap_regions
          storage_class: GLACIER
          data_age_days: 90
        - type: frequent_access
          regions: expensive_regions
          storage_class: STANDARD
          data_age_days: 0-90
```

### 7.2 Reserved Instances and Savings Plans

```yaml
reserved_instances:
  compute:
    - type: ec2
      region: us-east-1
      instance_types:
        - m5.xlarge
        - m5.2xlarge
      commitment: 3_year
      payment: partial_upfront
      quantity: 10
      estimated_savings: 60%
    - type: cloud_run
      region: us-east-1
      commitment: 1_year
      spend: 1000  # USD per month
      estimated_savings: 25%
  database:
    - type: rds
      region: us-east-1
      instance_class: db.r5.xlarge
      commitment: 3_year
      payment: all_upfront
      quantity: 3
      estimated_savings: 55%
```

### 7.3 Spot Instance Utilization

```yaml
spot_instances:
  enabled: true
  workloads:
    - name: batch_processing
      spot_enabled: true
      instance_types:
        - m5.xlarge
        - m5.2xlarge
      max_price: 0.5  # 50% of on-demand price
      fallback_to_on_demand: true
      capacity_rebalancing: true
    - name: background_jobs
      spot_enabled: true
      instance_types:
        - c5.xlarge
        - c5.2xlarge
      max_price: 0.4
      fallback_to_on_demand: true
      capacity_rebalancing: true
```

### 7.4 Auto-Scaling Optimization

```yaml
auto_scaling:
  policies:
    - name: api_servers
      min_instances: 2
      max_instances: 20
      target_cpu_percent: 70
      scale_up_cooldown: 300
      scale_down_cooldown: 600
      prediction: true  # Use ML to predict scaling needs
    - name: workers
      min_instances: 1
      max_instances: 50
      target_memory_percent: 80
      scale_up_cooldown: 60
      scale_down_cooldown: 300
      scheduled_scaling:
        - start_time: "09:00"
          end_time: "18:00"
          timezone: "UTC"
          min_capacity: 10
          days: [monday, tuesday, wednesday, thursday, friday]
```

## 8. Monitoring and Observability

### 8.1 Multi-Region Monitoring

```yaml
monitoring:
  enabled: true
  regions:
    - us-east-1
    - eu-west-1
    - ap-southeast-1
  metrics:
    - name: request_rate
      type: gauge
      aggregation: sum
      alert_threshold: 1000
    - name: error_rate
      type: gauge
      aggregation: avg
      alert_threshold: 0.01
    - name: latency_p95
      type: histogram
      alert_threshold: 500
    - name: replication_lag
      type: gauge
      alert_threshold: 1000  # ms
  dashboards:
    - name: regional_health
      refresh_interval: 30s
      panels:
        - title: Request Rate by Region
          type: graph
        - title: Error Rate by Region
          type: graph
        - Title: Replication Lag
          type: heatmap
```

### 8.2 Distributed Tracing

```yaml
tracing:
  enabled: true
  backend: jaeger
  sampling_rate: 0.01  # 1% of traces
  propagation_format: b3
  tags:
    - region
    - availability_zone
    - instance_id
```

### 8.3 Alerting and Notification

```yaml
alerting:
  enabled: true
  channels:
    - type: pagerduty
      severity: critical
      integration_key: PD_SECRET_KEY
    - type: slack
      severity: warning
      webhook_url: https://hooks.slack.com/services/...
    - type: email
      severity: info
      recipients:
        - ops-team@example.com
  rules:
    - name: region_down
      condition: region_health < 0.5
      severity: critical
      message: "Region {region} is unhealthy"
    - name: replication_lag_high
      condition: replication_lag > 1000
      severity: warning
      message: "Replication lag exceeds 1s in {region}"
```

## 9. Disaster Recovery Runbooks

### 9.1 Regional Outage

**Scenario:** Complete region failure (us-east-1)

**Runbook:**

1. **Detection:** Automated health check fails
2. **Alert:** On-call engineer notified via PagerDuty
3. **Assessment:** Verify outage scope and impact
4. **Failover:**
   - Execute automated failover to eu-west-1
   - Update DNS to point to eu-west-1
   - Verify traffic is flowing to eu-west-1
5. **Validation:**
   - Run smoke tests against eu-west-1
   - Monitor metrics for 30 minutes
   - Verify data integrity
6. **Communication:**
   - Update status page
   - Notify stakeholders
   - Document incident
7. **Recovery:**
   - Restore us-east-1 infrastructure
   - Resync data from eu-west-1
   - Run failback procedures
8. **Post-Mortem:**
   - Conduct incident review
   - Document root cause
   - Implement improvements

### 9.2 Database Replication Failure

**Scenario:** Replication lag exceeds 1 second

**Runbook:**

1. **Detection:** Replication lag alert fires
2. **Investigation:**
   - Check database metrics (CPU, memory, disk)
   - Review replication logs
   - Verify network connectivity
3. **Mitigation:**
   - Throttle write traffic if needed
   - Add read replicas to reduce load
   - Scale up database instance
4. **Resolution:**
   - Fix root cause (network, resources, configuration)
   - Wait for replication to catch up
   - Verify replication lag < 100ms
5. **Prevention:**
   - Add more monitoring
   - Increase capacity planning buffer
   - Improve alerting thresholds

### 9.3 Data Corruption

**Scenario:** Data corruption detected in regional database

**Runbook:**

1. **Detection:** Data integrity check fails
2. **Isolation:**
   - Stop writes to affected database
   - Promote healthy region to primary
   - Route traffic away from affected region
3. **Recovery:**
   - Restore from latest consistent backup
   - Replay transaction logs
   - Verify data integrity
4. **Validation:**
   - Run data integrity checks
   - Compare with other regions
   - Verify application functionality
5. **Prevention:**
   - Implement better validation
   - Add more frequent backups
   - Improve monitoring

## 10. Success Criteria

### 10.1 Availability

- **Target:** 99.99% uptime (43.8 minutes downtime/year)
- **Measurement:** Uptime monitoring across all regions
- **Success:** <5 minutes to failover, <1% failed requests

### 10.2 Performance

- **Target:** <100ms p95 latency for 95% of requests
- **Measurement:** Distributed tracing and metrics
- **Success:** Latency target met for all regions

### 10.3 Data Integrity

- **Target:** Zero data loss, <1 minute RPO
- **Measurement:** Replication lag monitoring
- **Success:** No data loss incidents, RPO < 1 minute

### 10.4 Compliance

- **Target:** 100% GDPR, HIPAA, SOC2 compliance
- **Measurement:** Annual audits and penetration tests
- **Success:** Pass all compliance audits

### 10.5 Cost Optimization

- **Target:** 30%+ cost reduction vs. single region
- **Measurement:** Monthly cost reports
- **Success:** Achieve 30% cost savings through optimization

## 11. Conclusion

This multi-region deployment architecture provides:

1. **High Availability:** 99.99% uptime with automatic failover
2. **Data Sovereignty:** GDPR-compliant data isolation
3. **Performance:** Low latency across global regions
4. **Resilience:** Automatic recovery from regional failures
5. **Cost Efficiency:** 30%+ savings through optimization

The architecture is designed to scale from 3 to 9+ regions as needed, with standardized patterns and automation to ensure consistency and reliability.

---

**Document Version:** 1.0
**Last Updated:** 2025-02-05
**Author:** Cloud Architecture Team
**Review Cycle:** Quarterly
