There are plenty of excellent documents on how to set up a Redis Master/Slave system, but very little on Sentinel.
Once you have Sentinel running reliably on the commend line, you will want to get Sentinel working as a service.
First, open up a new file:
vim /etc/systemd/system/sentinel.service
In there you probably want something like:
[Unit]
Description=Sentinel for Redis
After=network.target
[Service]
LimitNOFILE=64000
User=redis
Group=redis
ExecStart=/usr/local/bin/redis-sentinel /etc/redis/<your configuration file>.conf --daemonize no
[Install]
WantedBy=multi-user.target
You then need to make sure that the user you are using to run the service (in this case redis) has permissions for both the configuration file
chown redis:redis /etc/redis/<your configuration file>.conf
and the log files you have set up in your configuration file
chown redis:redis /var/log/redis/<your log file>.log
Test everything works as expected by:
systemctl start sentinel
then
systemctl status sentinel
You should get something that looks like:
If you do, then everything is good and you can set your service to start automatically with:
systemctl enable sentinel