Okay, some stuff needs te be in place before following this guide. I make the assumption you already know how to set those requirements up.

• minimum of 3 linux servers with:
  • root or sudo access
  • accessibility to ports 7000, 7001, 17000 and 17001
  • emacs installed (kidding of course, any editor will do)

The method of installing Redis comes down to the distribution you (have to) use. For a RedHat based distro, this will be:

sudo dnf install redis

For a Debian based distro, it's:

sudo apt install redis-server

Because Redis is an in-memory database we have to make some ajustments to the OS. These are mostly (exclusively?) changes in the way the systems handles memory related events.

With your favorite editor (another change to mention emacs?), create the file

/etc/rc.local

with the following content:

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
echo never > /sys/kernel/mm/transparent_hugepage/enabled
sysctl -w net.core.somaxconn=65535

exit 0

Next, edit the file

/etc/sysctl.conf

and add the following line to the end of the file:

vm.overcommit_memory=1

Now we've come to configuring Redis itself. First create some directories:

sudo mkdir /etc/redis/cluster
sudo mkdir /etc/redis/cluster/7000
sudo mkdir /var/lib/redis/7000
sudo mkdir /etc/redis/cluster/7001
sudo mkdir /var/lib/redis/7001

Then, make a config file for Redis on ports 7000 and 7001 (replace [PORT] with the respective port number):

/etc/redis/cluster/[PORT]/redis_[PORT].conf

For the content of these files, again replace [PORT] with the actual port number and set a secure password in place of [PASS].

port [PORT]
dir /var/lib/redis/[PORT]/
appendonly no
protected-mode no
cluster-enabled yes
cluster-node-timeout 5000
cluster-config-file /etc/redis/cluster/[PORT]/nodes_[PORT].conf
pidfile /var/run/redis/redis_[PORT].pid
logfile /var/log/redis/redis_[PORT].log
loglevel notice
requirepass [PASS]
masterauth [PASS]

Now give the redis user ownership and access rights to everything in the redis folders:

sudo chown redis:redis -R /var/lib/redis
sudo chmod 770 -R /var/lib/redis
sudo chown redis:redis -R /etc/redis

To start both redis instances (the one on port 7000 and the other on 7001) we need to create a service file for both: (again replace the [PORT] tag)

/etc/systemd/system/redis_[PORT].service

[Unit]
Description=Redis key-value database on [PORT]
After=network.target

[Service]
ExecStart=/usr/bin/redis-server /etc/redis/cluster/[PORT]/redis_[PORT].conf --supervised systemd
ExecStop=/bin/redis-cli -h 127.0.0.1 -p [PORT] shutdown
Type=notify
User=redis
Group=redis
RuntimeDirectory=redis
RuntimeDirectoryMode=0755
LimitNOFILE=65535

[Install]
WantedBy=multi-user.target

Lastly, disable the default redis service and enable both the 7000 and 7001 versions we just created. Don't forget to reload systemctl so we can access the new service files.

systemctl daemon-reload
systemctl disable redis
systemctl enable redis_7000
systemctl enable redis_7001

Then reboot, so all changes can take effect and the Redis instances will be started.

You now have 3 servers with 2 instances of Redis each. Last thing to do is cluster them together. The only thing you need is the IP adresses of these servers to use in this command:

redis-cli --cluster create IP1:7000 IP1:7001 IP2:7000 IP2:7001 IP3:7000 IP3:7001 --cluster-replicas 1 -a [PASS]

Don't forget to substitute the IP adresses and the password you used earlier. Type 'yes' to accept the configuration

From one of the servers login with the following command:

redis-cli -c -h IP -p 7000 -a [PASS]

On the redis-cli prompt, run the command:

CLUSTER NODES