I have tried all your ideas.
It seams not to be a curl issue. While setting SO_REUSEADDR the error Address already in use still occurs.
I also implemented guzzleHttp. Same problem there because guzzleHttp uses infact curl in the background.
I even have tried file_get_contents, it produces the same error.
So I tried multiple (2 to 10) instances that run ony one single curl / guzzleHttp or file_get_contents at the time.
Always gives the error somewhere between 30sec and 5min.
file get contents
$answer = file_get_contents($url);
curl
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT_MS, 250);
$answer = curl_exec($ch);
$curlInfo = curl_getinfo($ch);
curl_close($ch);
guzzleHttp
$client = new GuzzleHttp\Client();
$result = $client->request('GET', $url);
$statusCode = $result->getStatusCode();
$body = $result->getBody();
any ideas ?