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ADR-025-v4: Migration Strategy Architecture - Part 2 (Technical)

Document Specification Block​

Document: ADR-025-v4-migration-strategy-architecture-part2-technical
Version: 1.0.0
Purpose: Constrain AI implementation with exact technical specifications for migration strategies
Audience: AI agents, developers implementing migration systems
Date Created: 2025-09-01
Date Modified: 2025-09-01
QA Review Date: Pending
Status: DRAFT

Table of Contents​

  1. Constraints
  2. Dependencies
  3. Component Architecture
  4. Data Models
  5. Implementation Patterns
  6. API Specifications
  7. Testing Requirements
  8. Performance Benchmarks
  9. Security Controls
  10. Logging and Error Handling
  11. References
  12. Approval Signatures

1. Constraints​

CONSTRAINT: Zero Downtime​

All migrations MUST maintain 100% service availability throughout the process.

CONSTRAINT: Data Integrity​

99.999% data accuracy MUST be maintained with automated validation.

CONSTRAINT: Rollback Window​

System MUST support instant rollback (<60 seconds) at any migration phase.

CONSTRAINT: Performance Impact​

Migration overhead MUST NOT exceed 5% of system resources.

CONSTRAINT: Sync Latency​

Data replication lag MUST remain under 1 second during normal operation.

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2. Dependencies​

cargo.toml Dependencies​

[dependencies]
# Core async and database
tokio = { version = "1.35", features = ["full"] }
actix-web = "4.4"
foundationdb = { version = "0.8", features = ["embedded-fdb-include"] }

# Change Data Capture
debezium = "0.1"
rdkafka = { version = "0.34", features = ["cmake-build"] }

# Data transformation
serde = { version = "1.0", features = ["derive"] }
serde_json = "1.0"
arrow = "50.0"
datafusion = "35.0"

# Monitoring
prometheus = { version = "0.13", features = ["push"] }
opentelemetry = { version = "0.21", features = ["rt-tokio"] }

# Utilities
uuid = { version = "1.6", features = ["v4", "serde"] }
chrono = { version = "0.4", features = ["serde"] }
anyhow = "1.0"
thiserror = "1.0"
tracing = "0.1"

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3. Component Architecture​

// File: src/migration/orchestrator.rs
use std::sync::Arc;
use anyhow::Result;

pub struct MigrationOrchestrator {
    sync_engine: Arc<SyncEngine>,
    validator: Arc<DataValidator>,
    router: Arc<TrafficRouter>,
    monitor: Arc<MigrationMonitor>,
    rollback_manager: Arc<RollbackManager>,
    audit_logger: Arc<AuditLogger>,
}

// File: src/migration/orchestrator.rs
impl MigrationOrchestrator {
    pub async fn start_migration(
        &self,
        config: MigrationConfig,
    ) -> Result<MigrationSession> {
        // 1. Validate prerequisites
        self.validate_prerequisites(&config).await?;
        
        // 2. Initialize migration session
        let session = MigrationSession {
            id: Uuid::new_v4(),
            source: config.source_system,
            target: config.target_system,
            pattern: config.migration_pattern,
            started_at: Utc::now(),
            phase: MigrationPhase::Preparation,
        };
        
        // 3. Setup CDC pipeline
        let cdc_stream = self.sync_engine
            .setup_cdc(&config.source_system)
            .await?;
        
        // 4. Initialize validators
        self.validator
            .configure(&config.validation_rules)
            .await?;
        
        // 5. Start monitoring
        self.monitor
            .start_session_monitoring(&session)
            .await?;
        
        // 6. Audit log
        self.audit_logger.log_migration_event(
            "migration_started",
            &session.id,
            json!({
                "config": config,
                "pattern": config.migration_pattern
            })
        ).await?;
        
        Ok(session)
    }
    
    pub async fn execute_phase(
        &self,
        session: &MigrationSession,
        phase: MigrationPhase,
    ) -> Result<PhaseResult> {
        match phase {
            MigrationPhase::Preparation => self.execute_preparation(session).await,
            MigrationPhase::InitialSync => self.execute_initial_sync(session).await,
            MigrationPhase::Validation => self.execute_validation(session).await,
            MigrationPhase::ParallelRun => self.execute_parallel_run(session).await,
            MigrationPhase::Cutover => self.execute_cutover(session).await,
            MigrationPhase::Cleanup => self.execute_cleanup(session).await,
        }
    }
}

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4. Data Models​

Migration Models​

// File: src/models/migration.rs
use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MigrationConfig {
    pub source_system: SystemConfig,
    pub target_system: SystemConfig,
    pub migration_pattern: MigrationPattern,
    pub validation_rules: Vec<ValidationRule>,
    pub rollback_strategy: RollbackStrategy,
    pub performance_targets: PerformanceTargets,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum MigrationPattern {
    ParallelRun { duration_days: u32 },
    GradualCutover { phases: Vec<CutoverPhase> },
    BigBang { cutover_window: DateTime<Utc> },
    HybridCloud { on_premise_retention: Vec<String> },
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SyncState {
    pub source_position: String,  // CDC position/offset
    pub target_position: String,  // Last applied transaction
    pub lag_seconds: f64,
    pub pending_transactions: u64,
    pub sync_errors: Vec<SyncError>,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ValidationResult {
    pub timestamp: DateTime<Utc>,
    pub source_count: u64,
    pub target_count: u64,
    pub checksum_match: bool,
    pub discrepancies: Vec<DataDiscrepancy>,
    pub validation_duration_ms: u64,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct TrafficDistribution {
    pub legacy_percentage: f32,
    pub coditect_percentage: f32,
    pub routing_rules: Vec<RoutingRule>,
    pub sticky_sessions: bool,
}

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5. Implementation Patterns​

Change Data Capture (CDC)​

// File: src/migration/cdc.rs
use rdkafka::consumer::{Consumer, StreamConsumer};
use rdkafka::Message;

pub struct CDCProcessor {
    consumer: StreamConsumer,
    transformer: DataTransformer,
    target_writer: TargetWriter,
}

impl CDCProcessor {
    pub async fn process_changes(&self) -> Result<()> {
        loop {
            match self.consumer.recv().await {
                Ok(msg) => {
                    let change_event = self.parse_change_event(&msg)?;
                    let transformed = self.transformer
                        .transform(change_event)
                        .await?;
                    
                    self.target_writer
                        .apply_change(transformed)
                        .await?;
                    
                    self.consumer.commit_message(&msg, CommitMode::Async)?;
                }
                Err(e) => {
                    tracing::error!("CDC error: {}", e);
                    self.handle_cdc_error(e).await?;
                }
            }
        }
    }
}

Traffic Router​

// File: src/migration/router.rs
pub struct TrafficRouter {
    distribution: Arc<RwLock<TrafficDistribution>>,
    legacy_client: Arc<LegacyClient>,
    coditect_client: Arc<CoditectClient>,
}

impl TrafficRouter {
    pub async fn route_request(
        &self,
        request: IncomingRequest,
    ) -> Result<Response> {
        let dist = self.distribution.read().await;
        
        // Determine routing based on distribution
        let route_to_coditect = match &request {
            IncomingRequest::Read(_) => {
                // Use percentage-based routing for reads
                rand::random::<f32>() < dist.coditect_percentage / 100.0
            }
            IncomingRequest::Write(_) => {
                // Check if dual-write is enabled
                dist.coditect_percentage > 0.0
            }
        };
        
        if route_to_coditect {
            // Route to CODITECT
            let response = self.coditect_client
                .handle_request(request.clone())
                .await?;
            
            // Shadow write to legacy if needed
            if matches!(request, IncomingRequest::Write(_)) 
                && dist.legacy_percentage > 0.0 {
                tokio::spawn(async move {
                    let _ = self.legacy_client
                        .handle_request(request)
                        .await;
                });
            }
            
            Ok(response)
        } else {
            // Route to legacy
            self.legacy_client.handle_request(request).await
        }
    }
}

Data Validator​

// File: src/migration/validator.rs
pub struct DataValidator {
    source_reader: Arc<SourceReader>,
    target_reader: Arc<TargetReader>,
    rules: Vec<ValidationRule>,
}

impl DataValidator {
    pub async fn validate_consistency(&self) -> Result<ValidationResult> {
        let start = Instant::now();
        
        // Count validation
        let source_count = self.source_reader.count_records().await?;
        let target_count = self.target_reader.count_records().await?;
        
        // Checksum validation
        let source_checksum = self.calculate_checksum(&self.source_reader).await?;
        let target_checksum = self.calculate_checksum(&self.target_reader).await?;
        
        // Find discrepancies
        let discrepancies = if source_checksum != target_checksum {
            self.find_discrepancies().await?
        } else {
            vec![]
        };
        
        Ok(ValidationResult {
            timestamp: Utc::now(),
            source_count,
            target_count,
            checksum_match: source_checksum == target_checksum,
            discrepancies,
            validation_duration_ms: start.elapsed().as_millis() as u64,
        })
    }
}

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6. API Specifications​

Migration Control API​

// File: src/api/handlers/migration.rs
use actix_web::{web, HttpResponse, Result};

#[post("/api/v1/migrations")]
pub async fn start_migration(
    config: web::Json<MigrationConfig>,
    orchestrator: web::Data<Arc<MigrationOrchestrator>>,
    claims: Claims,
) -> Result<HttpResponse> {
    // Validate permissions
    if !claims.has_permission("migration:start") {
        return Ok(HttpResponse::Forbidden().json(json!({
            "error": "insufficient_permissions"
        })));
    }
    
    // Start migration
    match orchestrator.start_migration(config.into_inner()).await {
        Ok(session) => Ok(HttpResponse::Ok().json(session)),
        Err(e) => Ok(HttpResponse::BadRequest().json(json!({
            "error": e.to_string()
        })))
    }
}

#[get("/api/v1/migrations/{id}/status")]
pub async fn get_migration_status(
    path: web::Path<Uuid>,
    monitor: web::Data<Arc<MigrationMonitor>>,
    claims: Claims,
) -> Result<HttpResponse> {
    let migration_id = path.into_inner();
    
    match monitor.get_status(&migration_id).await {
        Ok(status) => Ok(HttpResponse::Ok().json(status)),
        Err(_) => Ok(HttpResponse::NotFound().json(json!({
            "error": "migration_not_found"
        })))
    }
}

#[post("/api/v1/migrations/{id}/rollback")]
pub async fn rollback_migration(
    path: web::Path<Uuid>,
    rollback_manager: web::Data<Arc<RollbackManager>>,
    claims: Claims,
) -> Result<HttpResponse> {
    let migration_id = path.into_inner();
    
    // Validate permissions
    if !claims.has_permission("migration:rollback") {
        return Ok(HttpResponse::Forbidden().json(json!({
            "error": "insufficient_permissions"
        })));
    }
    
    match rollback_manager.initiate_rollback(&migration_id).await {
        Ok(result) => Ok(HttpResponse::Ok().json(result)),
        Err(e) => Ok(HttpResponse::InternalServerError().json(json!({
            "error": e.to_string()
        })))
    }
}

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7. Testing Requirements​

Test Coverage Requirements​

  • Unit Test Coverage: ≥95% of migration logic
  • Integration Test Coverage: ≥90% of sync pipelines
  • E2E Test Coverage: All migration patterns tested
  • Performance Test Coverage: CDC throughput benchmarked
  • Chaos Test Coverage: Network partitions, data corruption

Integration Tests​

#[cfg(test)]
mod tests {
    use super::*;
    
    #[tokio::test]
    async fn test_parallel_run_migration() {
        let orchestrator = setup_test_orchestrator().await;
        
        // Start migration
        let config = MigrationConfig {
            migration_pattern: MigrationPattern::ParallelRun { 
                duration_days: 7 
            },
            ..Default::default()
        };
        
        let session = orchestrator.start_migration(config).await.unwrap();
        
        // Verify initial sync
        orchestrator.execute_phase(&session, MigrationPhase::InitialSync)
            .await.unwrap();
        
        // Validate data consistency
        let validation = orchestrator.execute_phase(
            &session, 
            MigrationPhase::Validation
        ).await.unwrap();
        
        assert!(validation.is_valid());
        assert_eq!(validation.discrepancy_count(), 0);
    }
    
    #[tokio::test]
    async fn test_rollback_during_cutover() {
        let orchestrator = setup_test_orchestrator().await;
        let session = create_test_session().await;
        
        // Start cutover
        let cutover_result = orchestrator.execute_phase(
            &session,
            MigrationPhase::Cutover
        ).await;
        
        // Simulate failure and rollback
        orchestrator.rollback_manager
            .initiate_rollback(&session.id)
            .await.unwrap();
        
        // Verify system reverted
        let status = orchestrator.monitor
            .get_status(&session.id)
            .await.unwrap();
        
        assert_eq!(status.phase, MigrationPhase::RolledBack);
        assert!(status.legacy_active);
    }
}

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8. Performance Benchmarks​

Required Metrics​

const MAX_SYNC_LAG_MS: u64 = 1000;
const MAX_CPU_OVERHEAD_PERCENT: f32 = 5.0;
const MIN_THROUGHPUT_RPS: u64 = 10000;

pub struct PerformanceValidator {
    pub async fn validate_migration_performance(&self) -> Result<ValidationReport> {
        let mut report = ValidationReport::default();
        
        // Test sync latency
        let lag = self.measure_sync_lag().await?;
        report.sync_lag_ok = lag.as_millis() <= MAX_SYNC_LAG_MS;
        
        // Test CPU overhead
        let overhead = self.measure_cpu_overhead().await?;
        report.cpu_overhead_ok = overhead <= MAX_CPU_OVERHEAD_PERCENT;
        
        // Test throughput
        let throughput = self.measure_throughput().await?;
        report.throughput_ok = throughput >= MIN_THROUGHPUT_RPS;
        
        Ok(report)
    }
}

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9. Security Controls​

Migration Security​

// File: src/migration/security.rs
pub struct MigrationSecurity {
    pub async fn validate_migration_access(
        &self,
        user: &AuthenticatedUser,
        operation: MigrationOperation,
    ) -> Result<()> {
        // Check role-based access
        match operation {
            MigrationOperation::Start => {
                if !user.has_role("migration_admin") {
                    return Err(SecurityError::InsufficientRole);
                }
            }
            MigrationOperation::Monitor => {
                if !user.has_role("migration_viewer") {
                    return Err(SecurityError::InsufficientRole);
                }
            }
            MigrationOperation::Rollback => {
                if !user.has_role("migration_admin") 
                    || !user.has_mfa_verified() {
                    return Err(SecurityError::MFARequired);
                }
            }
        }
        
        // Audit access
        self.audit_migration_access(user, operation).await?;
        
        Ok(())
    }
}

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10. Logging and Error Handling​

Migration Event Logging​

// File: src/migration/logging.rs
use tracing::{info, warn, error, instrument};

#[instrument(skip(self))]
pub async fn log_sync_progress(&self, state: &SyncState) {
    info!(
        source_position = %state.source_position,
        target_position = %state.target_position,
        lag_seconds = state.lag_seconds,
        pending_txns = state.pending_transactions,
        "Migration sync progress"
    );
}

pub async fn log_validation_result(&self, result: &ValidationResult) {
    if result.checksum_match {
        info!(
            source_count = result.source_count,
            target_count = result.target_count,
            duration_ms = result.validation_duration_ms,
            "Validation passed"
        );
    } else {
        warn!(
            discrepancy_count = result.discrepancies.len(),
            "Validation found discrepancies"
        );
    }
}

Error Handling​

#[derive(thiserror::Error, Debug)]
pub enum MigrationError {
    #[error("Sync lag exceeded threshold: {0} seconds")]
    ExcessiveLag(f64),
    
    #[error("Data validation failed: {0}")]
    ValidationFailed(String),
    
    #[error("Rollback failed: {0}")]
    RollbackFailed(String),
    
    #[error("Source system unavailable")]
    SourceUnavailable,
    
    #[error("Migration already in progress")]
    MigrationInProgress,
}

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11. References​

Version Compatibility​

  • FoundationDB: 7.1+ for transaction consistency
  • Debezium: 2.4+ for CDC capabilities
  • Kafka: 3.6+ for replication protocol

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12. Approval Signatures​

Technical Sign-off​

ComponentOwnerApprovedDate
ArchitectureSession5✓2025-09-01
ImplementationPending--
Security ReviewPending--
Performance TestPending--

Implementation Checklist​

  • CDC pipeline implemented
  • Sync engine functional
  • Data validator complete
  • Traffic router tested
  • Rollback mechanism verified
  • API endpoints operational
  • Performance benchmarks met
  • Security controls validated

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