Have you seen the config update in the latest release?
E.g. taken from the NS configuration: https://www.chirpstack.io/network-server/install/config/
# Redis settings
#
# Please note that Redis 2.6.0+ is required.
[redis]
# Server address or addresses.
#
# Set multiple addresses when connecting to a cluster.
servers=[
"localhost:6379",
]
# Password.
#
# Set the password when connecting to Redis requires password authentication.
password=""
# Database index.
#
# By default, this can be a number between 0-15.
database=0
# Redis Cluster.
#
# Set this to true when the provided URLs are pointing to a Redis Cluster
# instance.
cluster=false
# Master name.
#
# Set the master name when the provided URLs are pointing to a Redis Sentinel
# instance.
master_name=""
# Connection pool size.
#
# Default (when set to 0) is 10 connections per every CPU.
pool_size=0