Redis is a key-value database. Some applications, such as Rspamd, require Redis for data storage.

Install

The package ‘redis’ will install required dependencies.

sudo apt install redis

Now a Redis instance is running and listening on port 6379.

Memory overcommit

The Redis log /var/log/redis/redis-server.log will show the following warning.

# WARNING Memory overcommit must be enabled! Without it, a background save or replication may fail under low memory condition. Being disabled, it can also cause failures without low memory condition, see https://github.com/jemalloc/jemalloc/issues/1328. To fix this issue add ‘vm.overcommit_memory = 1’ to /etc/sysctl.conf and then reboot or run the command ‘sysctl vm.overcommit_memory=1’ for this to take effect.

If the server is mainly for Redis, change the setting accordingly.

  • In my case, I ignored the warning because the Redis workload is very low and the server provides multiple services (Other DB, Web, Mail…).
  • For more details, check the official Redis documentation.

In case you want to change the setting, follow the instructions below.

/etc/sysctl.conf does not exist on Debian 13, so create a config file /etc/sysctl.d/redis.conf and add the following line.

vm.overcommit_memory = 1

Activate the setting immediately.

sudo sysctl -p /etc/sysctl.d/redis.conf

Multiple instances

Instead of using multiple logical databases within a single instance, run a dedicated Redis instance for each service or application.
To run multiple instances, stop the default redis-server.service and run dedicated ones based on the default configuration.

Stop and disable the default instance

Stop the default instance and use the default configuration as a template.

sudo systemctl stop redis-server
sudo systemctl disable redis-server

Update configuration to use it as a template

Update /etc/redis/redis.conf to stop listening on the TCP socket by default.

# Accept connections on the specified port, default is 6379 (IANA #815344).
# If port 0 is specified Redis will not listen on a TCP socket.
port 0

Create a new configuration for each instance

Create a new configuration file for the new instance, such as /etc/redis/redis-rspamd.conf for Rspamd.

# Include template file as default
include /etc/redis/redis.conf

pidfile /run/redis/redis-server-rspamd.pid
logfile /var/log/redis/redis-server-rspamd.log

# Specify TCP port
port 6380

# Specify database dump file name
dbfilename dump-rspamd.rdb

# Limit memory usage
# - Max memory depends on the data and server memory size
# - Policy depends on the application (check the official documentation)
maxmemory 256mb
maxmemory-policy volatile-ttl

Change ownership of the newly created config file to redis:redis.

sudo chown redis:redis /etc/redis/redis-rspamd.conf
sudo chmod 640 /etc/redis/redis-rspamd.conf

systemd config

Add a service file for the new instance.

sudo systemctl enable redis-server@rspamd
sudo systemctl start redis-server@rspamd

Check the new instance status.

sudo systemctl status redis-server@rspamd