Redis for Cache, Session and Queue

Redis is a single in-memory key/value server, and three separate parts of Laravel can sit on it: the cache store, the session driver and the queue. They are configured independently, which is the part that catches people out.

Three settings, one server

Connections are named in the redis array of config/database.php. The shipped file defines default on database REDIS_DB (0) and cache on REDIS_CACHE_DB (1). CACHE_STORE=redis uses the connection named by REDIS_CACHE_CONNECTION in config/cache.php, which is cache. SESSION_DRIVER=redis uses the connection in SESSION_CONNECTION. QUEUE_CONNECTION=redis uses REDIS_QUEUE_CONNECTION, which defaults to default. Give each job its own database number, or at least its own prefix, and you can tell which keys belong to what.

Why the separation matters

Flushing the cache does not respect the cache prefix. Cache::flush(), and php artisan cache:clear with it, empties the store. If sessions and queued jobs share that database, clearing the cache signs out every user and deletes pending work. A memory limit with an eviction policy has the same problem: Redis evicts to make room and does not know that a queued job matters more than a cached count.

What a restart costs

Redis holds data in memory. With no persistence configured, a restart leaves an empty server. A cold cache is harmless, because the next request rebuilds it. An empty session store signs everyone out. An empty queue loses jobs that were waiting. If that is unacceptable, keep sessions and the queue on a persistent instance, or in the database, and let the volatile Redis hold only the cache.

<?php
// config/database.php

use Illuminate\Support\Str;

return [

    // ... connections, migrations and the rest of the file ...

    'redis' => [

        'client' => env('REDIS_CLIENT', 'phpredis'),

        'options' => [
            'cluster' => env('REDIS_CLUSTER', 'redis'),
            'prefix' => env('REDIS_PREFIX', Str::slug((string) env('APP_NAME', 'laravel')).'-database-'),
        ],

        // Queued jobs live here. This database must not evict keys.
        'default' => [
            'url' => env('REDIS_URL'),
            'host' => env('REDIS_HOST', '127.0.0.1'),
            'username' => env('REDIS_USERNAME'),
            'password' => env('REDIS_PASSWORD'),
            'port' => env('REDIS_PORT', '6379'),
            'database' => env('REDIS_DB', '0'),
        ],

        // The cache store. Safe to flush, safe to evict.
        'cache' => [
            'url' => env('REDIS_URL'),
            'host' => env('REDIS_HOST', '127.0.0.1'),
            'username' => env('REDIS_USERNAME'),
            'password' => env('REDIS_PASSWORD'),
            'port' => env('REDIS_PORT', '6379'),
            'database' => env('REDIS_CACHE_DB', '1'),
        ],

        // A third connection you add yourself, for sessions.
        'sessions' => [
            'url' => env('REDIS_URL'),
            'host' => env('REDIS_HOST', '127.0.0.1'),
            'username' => env('REDIS_USERNAME'),
            'password' => env('REDIS_PASSWORD'),
            'port' => env('REDIS_PORT', '6379'),
            'database' => env('REDIS_SESSION_DB', '2'),
        ],

    ],

];

REDIS_CLIENT=phpredis
REDIS_HOST=127.0.0.1
REDIS_PORT=6379

# Cache on database 1, through the 'cache' connection.
CACHE_STORE=redis
REDIS_CACHE_DB=1

# Sessions on database 2, through the 'sessions' connection you added.
SESSION_DRIVER=redis
SESSION_CONNECTION=sessions
SESSION_LIFETIME=120
REDIS_SESSION_DB=2

# Queue on database 0, through the 'default' connection.
QUEUE_CONNECTION=redis
REDIS_QUEUE_CONNECTION=default
REDIS_QUEUE=default

use Illuminate\Support\Facades\Cache;
use Illuminate\Support\Facades\Redis;

// The cache API on the redis store.
Cache::store('redis')->put('home.featured', $ids, 300);

// The same call through the helper.
cache()->store('redis')->put('home.featured', $ids, 300);

// Raw commands on a named connection, for structures the cache has no
// API for. These keys get the Redis options prefix, not the cache
// store's prefix, so Cache::get() will not find them.
Redis::connection('cache')->zadd('leaderboard', 120, 'user:42');

# The default store, prefix and all.
php artisan cache:clear

# A named store only.
php artisan cache:clear redis

# One key.
php artisan cache:forget home.featured

# One tag group, on a store that supports tags.
php artisan cache:clear --tags=reports

# Config, event, route and view caches AND the default cache store.
php artisan optimize:clear