Php versions – Connecting to ProxySQL via socket – "No such file or directory"

I am trying to connect to ProxySQL from PHP with mysqlnd using the local socket, but I get

“No such file or directory”

, as the socket would not exist. The same code can connect to the mysql socket with no problem.

Basically I am reproducing what was described at:
https://www.percona.com/blog/2017/09/19/proxysql-improves-mysql-ssl-connections/

<?php
$i = 10000;
$user = 'percona';
$pass = 'percona';
while($i>=0) {
 $mysqli = mysqli_init();

 // ProxySQL
 $link = mysqli_real_connect($mysqli, "localhost",      $user, $pass, "", 6033, "/tmp/proxysql.sock")
 or die(mysqli_connect_error());
 $info = mysqli_get_host_info($mysqli);
 $i--;
 mysqli_close($mysqli);
 unset($mysqli);
}
?>

This throws:

mysqli_real_connect(): (HY000/2002): No such file or directory

The socket file (/tmp/proxysql.sock) is in fact there:

$ ls -all /tmp
total 12
drwxrwxrwt. 11 root     root      4096 Oct  7 17:33 .
dr-xr-xr-x. 28 root     root      4096 Sep 20 17:42 ..
drwxrwxrwt.  2 root     root         6 Aug  8 02:40 .font-unix
drwxrwxrwt.  2 root     root         6 Aug  8 02:40 .ICE-unix
srwxrwxrwx   1 proxysql proxysql     0 Oct  7 17:11 proxysql.sock

I can use the mysql client to connect through it:

$ mysql -u myuser -p --socket /tmp/proxysql.sock --prompt='ProxySQLClient> '

If in the above PHP code I replace the socket file with the MySQL socket, then that works. It is only the proxysql.sock which doesn’t work with mysqlnd.

I am using:
mysqlnd version mysqlnd 5.0.12-dev – 20150407
ProxySQL version 2.0.6

Any idea why the proxysql.sock is not accepted by mysqlnd?

UPDATE: Following @EternalHour’s suggestion below, I have also tried moving the proxysql.sock file out of /tmp, but unfortunately that didn’t make a difference. I am still receiving the same error.

EDIT (2019-10-08): It turns out this issue has nothing to do with PHP, as netcat throws the same problem too, whether the socket files in in /tmp or in /var/sockets/:

$ nc -U /tmp/proxysql.sock
Ncat: No such file or directory.

Out of the 3 nodes of the ProxySQL cluster running on the same OS, same kernel version, 1 has this issue, the other 2 allows connection to the socket file in /tmp/proxsql.sock, although over there too, sometimes restarting ProxySQL results in the socket file being created as private (eg not available to other applications)