Scenario
Let Suppose a Scenario where we have a Redis Server (Version: redis-4.0.9) running on a Server with Redis Port 6388 and we want to upgrade this to latest Version( 5.0.8) without any downtime.Current location of existing installed Redis is /usr/local/bin/redis-server
Workaround
We will follow the following steps upgrading Redis Server without downtime.
1) Install a latest version(5.0.8) of Redis from source on the Same Server with a different installation location(/opt/local) without doing any changes on existing Redis Server .
2) Configure a different Redis Port 6399 on the newly Installed latest-Version Redis Server.
3) Make the existing old version- 4.0.9 Redis-Server as Master and newly installed Latest-Version-5.0.8 Redis Server as slave.
4)Verify the Master-Slave setup
5) Promote the SLAVE as Master.
6) Verify the new Master Server
7) Change the Redis Port on your Application.
Let us perform the above steps in details:
https://devopsmyway.com/upgrading-redis-with-zero-downtime/