Notice: Mastodon requires two kinds of cache. Sidekiq queues and home feeds, and the rails cache.
Large instances should consider running two or even separate Redis servers.

Working from https://docs.joinmastodon.org/admin/scaling/

Mastodon Server: maxmemory-policy: noeviction and appendonly yes, appendfsync everysec because we want to save the state.
Cache Server: `maxmemory-policy: allkeys-lru and save "" appendonly no` because we don’t care about state.
Sidekiq Server: xx

REDIS_URL (required for streaming)
CACHE_REDIS_URL (optional for ephemeral Rails cache)
SIDEKIQ_REDIS_URL (super optional for sidekiq)

Install Redis

sudo apt-get install lsb-release curl gpg
curl -fsSL https://packages.redis.io/gpg | sudo gpg --dearmor -o /usr/share/keyrings/redis-archive-keyring.gpg
sudo chmod 644 /usr/share/keyrings/redis-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/redis-archive-keyring.gpg] https://packages.redis.io/deb $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/redis.list
sudo apt-get update
sudo apt-get install redis

sudo systemctl enable redis-server
sudo systemctl start redis-server

Kernel tuning

# sudo nano /etc/sysctl.d/99-redis.conf

vm.overcommit_memory = 1
vm.swappiness = 1
net.core.somaxconn = 4096

Grub tuning

sudo nano /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="transparent_hugepage=never"
sudo update-grub
sudo reboot

Tune redis.conf

sudo nano /etc/redis/redis.conf
bind 127.0.0.1 <private-vlan-ip>
protected-mode yes
requirepass <long random string>

maxmemory <bytes> (Leave a 1Gb or so for the OS)
tcp-backlog 65536 (default 511)

Configure CPU Affinity (Optional)

On real CPUs, you can lay them out, but vCPUs on a hypervisor likely get moved around…. so not worth it?

sudo nano /etc/redis/redis.conf
server-cpulist 0-2
bio-cpulist 3-4
bgsave-cpulist 5-6
aof-rewrite-cpulist 7

Tune systemd service (Optional)

sudo nano /usr/lib/systemd/system/redis-server.service
[Service]
LimitNOFILE=65535

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shlee