Sentinel is not a load balacer, it switch replica to master when master is down.
Unfortunately Nextcloud don’t provide a detailed step-by-step guide on how to setup Sentinel and how to connect to it. Maybe it is because of Nextcloud is not Redis so Nextcloud don’t have the duty to do the job but I am pretty sure the business support line does provide a detailed tutorial.
This is the result I get from --latency-history
