Redis Connection Test: Failed

Hi there, thanks for the great plugin. I’m new to object cache and Redis, couldn’t make the connection test pass. Here is the screenshot of the failed connection test: https://imgur.com/AkLpYp7 . Here is the result of the “service redis status”:

service redis status
● redis-server.service - Advanced key-value store
   Loaded: loaded (/lib/systemd/system/redis-server.service; enabled; vendor preset: enabled)
   Active: active (running) since Sat 2019-08-24 00:11:03 CST; 4s ago
     Docs: https://redis.io/documentation,
           man:redis-server(1)
  Process: 28764 ExecStop=/bin/kill -s TERM $MAINPID (code=exited, status=0/SUCCESS)
  Process: 28768 ExecStart=/usr/bin/redis-server /etc/redis/redis.conf (code=exited, status=0/SUCCESS)
 Main PID: 28784 (redis-server)
    Tasks: 4 (limit: 1152)
   CGroup: /system.slice/redis-server.service
           └─28784 /usr/bin/redis-server 127.0.0.1:6379

Aug 24 00:11:03 shcces2 systemd[1]: Starting Advanced key-value store...
Aug 24 00:11:03 shcces2 systemd[1]: redis-server.service: Can't open PID file /var/run/redis/redis-server.pid (yet?) after start: No such file or directory
Aug 24 00:11:03 shcces2 systemd[1]: Started Advanced key-value store.

I notice the “Can’t open PID file /var/run/redis/redis-server.pid” error, but when I look into the /var/run folder, I found:

drwxr-sr-x 2 redis www-data 80 Aug 24 00:11 redis/

inside it, there is:

-rw-rw----  1 redis www-data    6 Aug 24 00:11 redis-server.pid
srwxrwxr-x  1 redis www-data    0 Aug 24 00:11 redis-server.sock=

I tried to remove the redis folder and restart redis. The folder will be re-generated with the same content. Is this the cause? How can I fix it?

Here is the result of: ss -lptun | grep 6379

ss -lptun | grep 6379
tcp    LISTEN   0        128             127.0.0.1:6379           0.0.0.0:*      users:(("redis-server",pid=28784,fd=6))                                        
tcp    LISTEN   0        128                 [::1]:6379              [::]:*      users:(("redis-server",pid=28784,fd=7)) 

“telnet localhost 6379” and “redis-cli ping” work fine.