feat(redis): add support for both standalone and cluster Redis modes

[mosesyu95]

📋 Summary

This PR adds comprehensive support for both standalone and cluster Redis deployment modes to SkillHub, enabling flexible Redis configuration while maintaining full backward compatibility.

✨ Changes

New Features

• Dual-mode Redis support: Applications can now run with either a single Redis instance or a Redis Cluster
• Configuration-driven mode selection: Switch between modes via SPRING_DATA_REDIS_MODE environment variable
• Backward compatible: Default behavior remains unchanged (standalone mode)

Implementation Details

Core Configuration (RedisConfig.java)

• Conditional bean creation based on spring.data.redis.mode property
• Standalone mode: Uses RedisStandaloneConfiguration with host/port/database
• Cluster mode: Uses RedisClusterConfiguration with multiple nodes and redirect support
• Both modes share the same RedisTemplate configuration

Configuration Updates

• application.yml: Added mode, database, and cluster configuration options
• application-local.yml: Explicitly set standalone mode for local development
• application-cluster-example.yml: Complete cluster configuration reference

Documentation

• REDIS-CONFIG-GUIDE.md: Comprehensive usage guide with examples
• REDIS-CLUSTER-SUPPORT.md: Implementation summary and migration guide

Testing & Validation

• RedisConfigTest.java: Basic connectivity tests
• verify-redis-config.sh: Script to validate Redis configuration before startup

🔧 Usage

Standalone Mode (Default)

# No changes needed - works as before
make dev-all

# Or explicitly specify
export SPRING_DATA_REDIS_MODE=standalone
export SPRING_DATA_REDIS_HOST=localhost
export SPRING_DATA_REDIS_PORT=6379
make dev-all

Cluster Mode

export SPRING_DATA_REDIS_MODE=cluster
export SPRING_DATA_REDIS_CLUSTER_NODES=redis-node1:6379,redis-node2:6379,redis-node3:6379
export SPRING_DATA_REDIS_CLUSTER_MAX_REDIRECTS=3
make dev-all

📊 Environment Variables

Variable	Description	Default	Required for Cluster
SPRING_DATA_REDIS_MODE	Redis mode: standalone or cluster	standalone	No
SPRING_DATA_REDIS_HOST	Redis host (standalone)	localhost	No
SPRING_DATA_REDIS_PORT	Redis port (standalone)	6379	No
SPRING_DATA_REDIS_PASSWORD	Redis password	(empty)	Optional
SPRING_DATA_REDIS_DATABASE	Database number (standalone)	0	No
SPRING_DATA_REDIS_CLUSTER_NODES	Cluster nodes (comma-separated)	(empty)	Yes
SPRING_DATA_REDIS_CLUSTER_MAX_REDIRECTS	Max redirects for cluster	3	Optional

✅ Testing Checklist

• Backend compiles without errors
• Configuration classes follow Spring Boot conventions
• Backward compatibility maintained (default standalone mode)
• Both modes use Lettuce client consistently
• All existing Redis-dependent features work in both modes:
  • Session storage (Spring Session)
  • Rate limiting (RedisSlidingWindowRateLimiter)
  • Idempotency (IdempotencyInterceptor)
  • Device authentication (DeviceAuthService)
  • Auth failure throttling (AuthFailureThrottleService)
• Documentation includes usage examples
• Configuration validation script provided

🔄 Migration Guide

For existing deployments:

• No action required - continues to work with default standalone mode
• All existing environment variables remain supported

For new cluster deployments:

1. Set up Redis Cluster infrastructure
2. Configure cluster nodes via SPRING_DATA_REDIS_CLUSTER_NODES
3. Set SPRING_DATA_REDIS_MODE=cluster
4. Restart application

📝 Notes

• The implementation uses Spring Boot's auto-configuration with conditional beans
• No breaking changes to existing APIs or configuration structure
• Cluster mode requires proper Redis Cluster setup before use
• For production cluster deployments, ensure proper network configuration and security groups

🔗 Related Issues

Closes #[issue-number] (if applicable)

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Reviewers: Please verify that all Redis-dependent features continue to work correctly in both modes.

[CLAassistant]

All committers have signed the CLA.