For PHP web applications requiring high availability Redis storage, Redis Cluster (introduced in Redis 3+) provides automatic sharding and failover capabilities. While early versions had stability concerns, Redis 5+ has significantly improved production readiness with:

• Automatic data partitioning across multiple nodes
• Master-replica replication with failover
• Linear scalability up to 1000 nodes

When implementing Redis Cluster for PHP session storage:

// Sample PHPRedis cluster configuration
$redis = new RedisCluster(
    null,
    [
        'redis-node1:6379',
        'redis-node2:6379',
        'redis-node3:6379'
    ],
    1.5, // Timeout
    1.5, // Read timeout
    false, // Persistent
    'auth_password'
);

// Session handler configuration
ini_set('session.save_handler', 'redis');
ini_set('session.save_path', 'tcp://redis-node1:6379?auth=password,tcp://redis-node2:6379?auth=password');

Key recommendations for Redis in load-balanced PHP environments:

1. Use pipelining for batch operations:

   $redis->multi(Redis::PIPELINE)
       ->set('session:1', $data1)
       ->set('session:2', $data2)
       ->exec();

2. Configure appropriate timeout values (typically 1-3x your average operation time)
3. Monitor memory fragmentation ratio and eviction policies

Essential metrics to track in production:

• Cluster state using redis-cli --cluster check
• Replication lag with INFO replication
• Node health via PING responses

For automated failover integration with pfSense:

#!/bin/bash
# Basic health check script for pfSense
if ! redis-cli -h $REDIS_MASTER PING | grep -q PONG; then
    pfctl -F states -t redis_states
    # Trigger load balancer reconfiguration
fi

Redis Cluster has significantly matured since its introduction in Redis 3.0. While early versions had limitations for production use, current implementations (Redis 5+) offer robust solutions for:

• Automatic sharding across multiple nodes
• Master-replica replication with failover
• Partial resynchronization after network partitions

For PHP web applications requiring high availability, consider these proven architectures:

// Sample PHPRedis cluster configuration
$redis = new RedisCluster(
    null,
    [
        'redis-node1:6379',
        'redis-node2:6379',
        'redis-node3:6379',
    ],
    1.5, // timeout
    1.5, // read_timeout
    false, // persistent
    'password'
);

For PHP session storage in load-balanced environments:

// Configure PHP to use Redis for sessions
ini_set('session.save_handler', 'redis');
ini_set('session.save_path', 'tcp://redis-cluster:6379?auth=password&persistent=1');

// Alternative using PHPRedis
$redis = new Redis();
$redis->pconnect('redis-cluster', 6379);
$redis->auth('password');
session_set_save_handler(
    [$redis, 'sessionOpen'],
    [$redis, 'sessionClose'],
    [$redis, 'sessionRead'],
    [$redis, 'sessionWrite'],
    [$redis, 'sessionDestroy'],
    [$redis, 'sessionGC']
);

Benchmark your Redis cluster configuration under production-like loads:

• Test failover scenarios (kill -9 master processes)
• Measure latency during resharding operations
• Validate cross-datacenter performance if applicable

Here's a Docker Compose snippet for testing Redis Cluster:

version: '3'
services:
  redis-node1:
    image: redis:6
    command: redis-server --cluster-enabled yes --cluster-config-file nodes-node-1.conf --port 6379
  redis-node2:
    image: redis:6
    command: redis-server --cluster-enabled yes --cluster-config-file nodes-node-2.conf --port 6379
  redis-cluster-init:
    image: redis:6
    command: redis-cli --cluster create redis-node1:6379 redis-node2:6379 --cluster-replicas 1
    depends_on:
      - redis-node1
      - redis-node2

1. For new deployments, use Redis 7+ Cluster with PHPRedis 5.3+
2. Implement circuit breakers in your PHP application
3. Monitor cluster health with Prometheus and Grafana