🧭 Epic

Title: Add Optional Persistence Support for PostgreSQL and Redis

Goal: Provide production-ready persistence configuration for PostgreSQL and Redis in the Helm chart with proper templating, backup annotations, and conditional logic.

Why now:

• Production deployments require persistent storage to survive pod restarts
• Need Velero/backup tool integration for disaster recovery
• Current implementation needs verification and documentation

Current State:
✅ This feature appears to be implemented!

The Helm chart already includes:

• postgres-pvc.yaml with proper templating
• redis-pvc.yaml with proper templating
• values.yaml persistence configuration for both PostgreSQL and Redis
• Velero annotation support
• Configurable storage class, size, and reclaim policy

📖 User Stories

Scenario: PostgreSQL data persists across restarts
  Given postgres.persistence.enabled = true
  When the PostgreSQL pod is restarted
  Then all database data should be preserved
  And no manual data recovery should be needed

Scenario: Configure storage class
  Given postgres.persistence.storageClassName = "gp3"
  When the PVC is created
  Then it should use the gp3 storage class

Scenario: Disable persistence for testing
  Given postgres.persistence.enabled = false
  When the PostgreSQL pod is deployed
  Then it should use emptyDir volume
  And data should be lost on pod restart

Scenario: Redis ephemeral mode (default)
  Given redis.persistence.enabled = false (default)
  When Redis pod restarts
  Then cache should be empty (expected behavior for caching)

Scenario: Redis persistent mode
  Given redis.persistence.enabled = true
  When Redis pod restarts
  Then cached data should be preserved
  And session data should survive restarts

Scenario: Velero backup annotation
  Given postgres.persistence.annotations contains:
    backup.velero.io/backup-volumes: "postgres-data"
  When Velero runs a backup
  Then the PostgreSQL volume should be included
  And the backup should complete successfully

Scenario: Custom annotations
  Given I add custom annotations in values.yaml
  When the PVC is created
  Then all annotations should be present on the PVC

🏗 Architecture

Persistence Configuration Flow

flowchart TD
    subgraph values.yaml
        A[postgres.persistence.enabled]
        B[redis.persistence.enabled]
    end
    
    subgraph Templates
        A -->|true| C[postgres-pvc.yaml]
        A -->|false| D[emptyDir volume]
        B -->|true| E[redis-pvc.yaml]
        B -->|false| F[emptyDir volume]
    end
    
    subgraph Storage
        C --> G[PersistentVolume]
        E --> H[PersistentVolume]
    end

Current Implementation

# PostgreSQL Persistence (charts/mcp-stack/values.yaml:828)
postgres:
  persistence:
    enabled: true
    storageClassName: ""
    accessModes: [ReadWriteOnce]
    size: 5Gi
    reclaimPolicy: Retain
    annotations: {}

# Redis Persistence (charts/mcp-stack/values.yaml:1018)
redis:
  persistence:
    enabled: false  # Default: caching mode
    storageClassName: ""
    accessModes: [ReadWriteOnce]
    size: 1Gi
    reclaimPolicy: Retain
    annotations: {}

📋 Implementation Tasks

Verification Tasks (Feature Exists)

• Verify postgres-pvc.yaml template works correctly
• Verify redis-pvc.yaml template works correctly
• Verify emptyDir fallback when persistence disabled
• Test with different storage classes
• Test Velero backup annotations

Documentation Tasks

• Document PostgreSQL persistence configuration
• Document Redis persistence options
• Document storage class examples for AWS, GCP, Azure
• Document backup integration with Velero
• Add troubleshooting section

Potential Enhancements

• Add Redis AOF/RDB configuration options
• Add volume snapshot support
• Add PV reclaim policy configuration in deployment templates
• Add data migration documentation

⚙️ Configuration Examples

Production Configuration (AWS EKS)

postgres:
  persistence:
    enabled: true
    storageClassName: "gp3"
    size: 50Gi
    reclaimPolicy: Retain
    annotations:
      backup.velero.io/backup-volumes: "postgres-data"

redis:
  persistence:
    enabled: false  # Ephemeral caching

Stateful Redis Configuration

redis:
  persistence:
    enabled: true
    storageClassName: "gp3"
    size: 10Gi
    reclaimPolicy: Retain
    annotations:
      backup.velero.io/backup-volumes: "redis-data"

Development/Testing Configuration

postgres:
  persistence:
    enabled: false  # Use emptyDir

redis:
  persistence:
    enabled: false

✅ Success Criteria

• PostgreSQL persistence works with enabled: true
• PostgreSQL uses emptyDir with enabled: false
• Redis persistence works with enabled: true
• Redis uses emptyDir with enabled: false
• Storage class configuration works
• Velero backup annotations work
• Documentation complete with examples

🏁 Definition of Done

• Verify existing implementation works correctly
• Test PostgreSQL persistence on/off scenarios
• Test Redis persistence on/off scenarios
• Test with real storage classes (gp3, standard, etc.)
• Test Velero backup integration
• Documentation updated in charts/README.md
• Add examples for AWS, GCP, Azure storage classes
• PR reviewed and approved

📝 Implementation Status

🔗 Related Issues

• Helm chart enhancements
• Backup and disaster recovery
• Production deployment guide