Shared Cache

FnKit includes a shared cache powered by Valkey — a Redis-compatible, open-source key-value store maintained by the Linux Foundation. All function containers on fnkit-network can access it with sub-millisecond latency.

Architecture 

Function containers ──→ fnkit-cache:6379 (Valkey)
                         ├── Sub-millisecond reads/writes
                         ├── TTL support (auto-expire keys)
                         ├── Persistent (snapshots to disk)
                         └── 256 MB max memory (LRU eviction)

Quick Start 

# Create cache project files
fnkit cache init

# Start the cache
fnkit cache start

# Verify it's running
docker exec fnkit-cache valkey-cli ping
# → PONG

All function containers on fnkit-network can now connect at:

redis://fnkit-cache:6379

The CACHE_URL environment variable is automatically set in generated Dockerfiles.

Configuration

Setting Default Description
Max memory 256 MB Configurable via --maxmemory flag
Eviction policy allkeys-lru Least recently used keys evicted when full
Persistence RDB snapshots Saves to disk every 60s if ≥1 key changed
Port 6379 Standard Redis port

Custom Memory Limit 

fnkit cache start --maxmemory 512mb

Connecting from Functions

Every generated function template includes a commented-out cache example. Uncomment it and install the client library for your language.

Node.js 

npm install ioredis

const Redis = require('ioredis')
const cache = new Redis(process.env.CACHE_URL || 'redis://fnkit-cache:6379')

await cache.set('key', 'value', 'EX', 300) // expires in 5 minutes
const value = await cache.get('key')

Python 

pip install redis

import os, redis
cache = redis.from_url(os.environ.get('CACHE_URL', 'redis://fnkit-cache:6379'))

cache.set('key', 'value', ex=300)
value = cache.get('key')

Go 

go get github.com/redis/go-redis/v9

import "github.com/redis/go-redis/v9"

rdb := redis.NewClient(&redis.Options{Addr: "fnkit-cache:6379"})
rdb.Set(ctx, "key", "value", 5*time.Minute)
value, _ := rdb.Get(ctx, "key").Result()

Java

Add jedis to your pom.xml:

import redis.clients.jedis.Jedis;

Jedis cache = new Jedis("fnkit-cache", 6379);
cache.setex("key", 300, "value");
String value = cache.get("key");

Ruby 

gem install redis

require 'redis'
cache = Redis.new(url: ENV.fetch('CACHE_URL', 'redis://fnkit-cache:6379'))

cache.set('key', 'value', ex: 300)
value = cache.get('key')

.NET 

dotnet add package StackExchange.Redis

using StackExchange.Redis;

var redis = ConnectionMultiplexer.Connect("fnkit-cache:6379");
var db = redis.GetDatabase();
db.StringSet("key", "value", TimeSpan.FromMinutes(5));
var value = db.StringGet("key");

PHP 

composer require predis/predis

require 'vendor/autoload.php';
$cache = new Predis\Client(getenv('CACHE_URL') ?: 'redis://fnkit-cache:6379');

$cache->setex('key', 300, 'value');
$value = $cache->get('key');

Managing the Cache 

# Stop the cache (data persists in Docker volume)
fnkit cache stop

# Test with CLI
docker exec fnkit-cache valkey-cli SET hello world
docker exec fnkit-cache valkey-cli GET hello

# Monitor stats
docker exec fnkit-cache valkey-cli INFO stats

# Flush all data
docker exec fnkit-cache valkey-cli FLUSHALL

# Remove persisted data
docker volume rm fnkit-cache-data

Why Valkey?

Valkey is the community fork of Redis, maintained by the Linux Foundation with backing from AWS, Google, Oracle, and others. It’s wire-protocol compatible with Redis — every Redis client library works unchanged. Fully open source under the BSD license.

Notes

  • Cache data persists in the fnkit-cache-data Docker volume (survives restarts)
  • All function containers on fnkit-network can access the cache
  • No authentication by default (internal network only)
  • The cache container is labelled fnkit.cache=true for easy identification