🧠 Mini-Redis (Distributed In-Memory Store)

A high-performance, distributed key-value store written in Go, compatible with the Redis RESP protocol. This project implements core distributed systems concepts including Leader-Follower Replication, Automatic Failover (Raft-lite), AOF Persistence, and a Smart Client for topology-aware routing.

It is designed to be a learning resource for understanding how distributed databases work under the hood.

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✨ Key Features

🚀 Core Engine

• RESP Protocol Compatible: Works with standard redis-cli and Redis libraries.
• In-Memory Storage: Fast key-value operations.
• TTL Support: Keys expire automatically after a set time.
• LRU Eviction: Automatically removes old keys when memory limit is reached.

🛡️ Distributed Architecture

• Replication: One Leader (Writes) + Multiple Replicas (Reads).
• Automatic Failover: If the Leader crashes, the cluster detects it and elects a new Leader automatically using a quorum-based election (similar to Raft).
• Split-Brain Protection: Uses Epoch (Term) numbers to reject stale leaders.

💾 Persistence

• AOF (Append-Only File): Durability ensures data isn't lost on restart.
• Background Rewrite: BGREWRITEAOF compacts logs without blocking the main thread.

🧠 Smart Client

• Topology Discovery: Automatically finds the Leader and Replicas.
• Read/Write Splitting: Routes SET commands to the Leader and GET commands to Replicas (Round-Robin).
• Auto-Retry: Seamlessly handles failovers with automatic retries, providing near-zero downtime to the application.

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🏗️ Architecture

The system runs as a cluster of nodes. An external load balancer (HAProxy) is provided for legacy clients, while modern applications use the Smart Client.

                               ┌─────────────────┐
                               │  Application    │
                               │ (Smart Client)  │
                               └────────┬────────┘
                   ┌────────────────────┼────────────────────┐
                   │                    │                    │
          ┌────────▼────────┐  ┌────────▼────────┐  ┌────────▼────────┐
          │  Redis Node 1   │  │  Redis Node 2   │  │  Redis Node 3   │
          │    (Leader)     │◄─┤    (Replica)    │◄─┤    (Replica)    │
          └─────────────────┘  └─────────────────┘  └─────────────────┘
                   ▲
                   │
           ┌───────┴───────┐
           │    HAProxy    │◄─── Standard redis-cli
           └───────────────┘

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🚀 Getting Started

The easiest way to run the cluster is using Docker Compose. This spins up 3 Redis nodes, an HAProxy load balancer, and an example client application.

Prerequisites

• Docker & Docker Compose
• redis-cli (optional, for manual testing)

1. Start the Cluster

docker-compose up --build

You will see logs from 3 redis nodes, haproxy, and the example client.

2. Connect Manually (via CLI)

You can connect to the cluster using the standard Redis CLI through the HAProxy load balancer on port 6379.

redis-cli -p 6379

Try running commands:

SET mykey "Hello Distributed World"
GET mykey
INFO replication

3. Smart Client Demo

The client-app service in Docker demonstrates the Go Smart Client. It connects to the cluster, performs writes to the leader, and reads from replicas. Check the docker logs:

client-app_1  | Initializing Smart Client...
client-app_1  | Connected! Starting workload...
client-app_1  | [WRITE] SET framework mini-redis-client
client-app_1  | [READ] GET framework = mini-redis-client

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🎮 Testing Failover

You can simulate a crash to see the system recover automatically.

1. Check who is the leader:

   redis-cli -p 6379 INFO replication
   # Output: role:leader (and check the container logs to see which node this is, e.g., redis-1)

2. Kill the Leader: Stop the container corresponding to the leader (e.g., redis-1).

   docker-compose stop redis-1

3. Watch the Election: Observe the logs of the other nodes (redis-2, redis-3).

   • They will detect the master is down.
   • Start an election.
   • One will become the new Leader.

4. Verify Client Recovery:

   • HAProxy: Will automatically switch traffic to the new leader after a brief check interval.
   • Smart Client: Will catch the connection error, refresh its topology map, and retry the operation against the new leader automatically.

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📜 Supported Commands

Command	Usage	Description
SET	SET key value [EX seconds]	Set a key with optional TTL.
GET	GET key	Get the value of a key.
DEL	DEL key	Delete a key.
TTL	TTL key	Get remaining time to live (in seconds).
EXISTS	EXISTS key	Check if a key exists (1) or not (0).
PING	PING	Returns PONG.
INFO	INFO [section]	Get server info (replication, memory, stats).
CONFIG	CONFIG GET/SET param	Get or set configuration (e.g., maxmemory).

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💻 Development (Running Locally)

If you want to run without Docker (e.g., for development), you can start nodes manually.

1. Build:

go build -o mini-redis cmd/server/main.go

2. Start Leader (Port 6379):

./mini-redis -port 6379 -peers "localhost:6380,localhost:6381"

3. Start Replicas:

./mini-redis -port 6380 -peers "localhost:6381, localhost:6379"
./mini-redis -port 6381 -peers "localhost:6380, localhost:6379"

(Note: Replicas will auto-discover the leader via the peers list or need REPLICAOF command manually if not using the discovery logic).

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Summary:

• redis-cli -> HAProxy -> Leader (Writes & Reads)
• client-app (Smart Client) -> Leader (Writes) / Replicas (Reads)

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📁 Project Structure

mini-redis/
├── cmd/
│   ├── server/          # Main entry point for the Server
│   └── example-client/  # Demo application using the Smart Client
├── internal/
│   ├── server/          # Core logic: Event loop, Replication, Election, TCP
│   ├── store/           # In-memory data structures (Map, TTL, LRU)
│   ├── persistence/     # AOF file handling
│   └── protocol/        # RESP parser & writer
├── client/              # 📦 Go Smart Client Library
├── docker-compose.yml   # Cluster orchestration
├── Dockerfile           # Server container definition
├── Dockerfile.client    # Client container definition
└── haproxy.cfg          # Load Balancer configuration