I get some strange errors from nbd_redis but my setup is working. kamailio 5.3.5 on CentOS 7.7.1908.
Redis-Server is an haproxy frontend that pushed the stuff to an redis-sentinel cluster (with and really old version redis-3.2.1-2.el7.remi.x86_64).
Jul 22 13:42:52 siptrunk5 kamailio[112377]: ERROR: ndb_redis [redis_client.c:1083]: redisc_exec_argv(): Redis error: Server closed the connection
Jul 22 13:43:34 siptrunk5 kamailio[112359]: ERROR: ndb_redis [redis_client.c:1083]: redisc_exec_argv(): Redis error: Server closed the connection
Jul 22 13:43:34 siptrunk5 kamailio[112378]: ERROR: ndb_redis [redis_client.c:1083]: redisc_exec_argv(): Redis error: Server closed the connection
Jul 22 13:44:33 siptrunk5 kamailio[112363]: ERROR: ndb_redis [redis_client.c:1083]: redisc_exec_argv(): Redis error: Server closed the connection
Jul 22 13:45:03 siptrunk5 kamailio[112362]: ERROR: ndb_redis [redis_client.c:1083]: redisc_exec_argv(): Redis error: Server closed the connection
Jul 22 14:00:01 siptrunk5 kamailio[112381]: ERROR: ndb_redis [redis_client.c:1083]: redisc_exec_argv(): Redis error: Server closed the connection
Jul 22 14:00:01 siptrunk5 kamailio[112365]: ERROR: {24519 CANCEL 59644df6-68ac-4dd6-9fa5-1a9c2eda3b59} ndb_redis [redis_client.c:1083]: redisc_exec_argv(): Redis error: Server closed the connection
# grep redis /etc/kamailio/kamailio.cfg
loadmodule "ndb_redis.so"
loadmodule "topos_redis.so"
modparam("ndb_redis", "server", "name=CFG_REDIS_NAME;addr=CFG_REDIS_ADDR;port=6379;db=CFG_REDIS_DB")
modparam("ndb_redis", "connect_timeout", 1500) # default 1000ms/1sec
modparam("ndb_redis", "cmd_timeout", 1500) # default 1000ms/1sec
modparam("topos", "storage", "redis")
modparam("topos_redis", "serverid", "CFG_REDIS_NAME")
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