PHP file_get_contents sometimes returns 502 on 1 of 2 Servers

I have two virtual servers.

The old: Ubuntu 12.04 with PHP 7.2. The new: CentOS 7.9 with PHP 8.0.

On both servers the same application is running. A cron is minutely getting some details from another website. similar to the following code

file_get_contents("http://mirror.facebook.net/centos/timestamp.txt")

On the old server, it worked well. I never had issues. On the new server, I have sometimes this Message

Warning: file_get_contents(mirror.facebook.net/centos/timestamp.txt): Failed to open stream: HTTP request failed! HTTP/1.0 502 Bad Gateway

I have no idea why this happens. It affects about 1% of the calls.

Does anyone have an idea where I could look and what I could do to solve the issue?

[EDIT] I implemented the error and time tracking as mentioned below.

First the code:

$t0 = microtime(true);
$jsonString = file_get_contents($pageUrl);
if ($jsonString === false) {
    $t1 = microtime(true);
    var_dump(sprintf(
        'Fehler beim Abruf der URL %s',
        $pageUrl,
    ));
    var_dump($t1 - $t0);
    var_dump(error_get_last());

    return 0;
}

Now the result.

array(4) {
  ["type"]=>
  int(2)
  ["message"]=>
  string(145) "file_get_contents(https://www.example.com/): Failed to open stream: HTTP request failed! HTTP/1.0 502 Bad Gateway
"
  ["file"]=>
  string(62) "/path/to/src/Service/WebcrawlerService.php"
  ["line"]=>
  int(61)
}

The result is sadly NOT providing many more details. It's still 502

I suspect your new server is hitting some sporadic network timeout (DNS?). To dig deeper, try to log a detailed error right after failing file_get_contents() and duration of the request before the failure:

$t0 = microtime(true);
if (($data = @file_get_contents("http://mirror.facebook.net/centos/timestamp.txt")) === false) {
    $t1 = microtime(true);
    var_dump($t1 - $t0);  // duration
    var_dump(error_get_last());
}

These outputs combined might give you hints about further steps.